LAYOUT IS APPARENTLY NOT IN A MOOD TO CO-OPERATE
My arbitrary deadline to do the second half of the lacewings came and went so I suppose the most agriculturally relevant (albeit a little less exciting to photograph) chapter on that order will be next June. Which means I have another year to get pictures of the Coniopterygids! Yay!
I'm going to be radical (...) and go from the least massive of the 5 most abundant orders of the Endopterygota (insects that undergo full metamorphosis - including most of the most speciose orders) to the largest order of the Exopterygota (all other insects, which undergo partial metamorphosis): the Bugs.
The Pentotomoidea
OR
Yes, there IS such a thing as a Bug
OR
OR
Insects in Agriculture, Part 2 of Many
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| Potato Shieldbug, Caura rufiventris in garden in Chongwe, Lusaka Province, Zambia. |
While the lacewings, when they aren't irrelevant to agriculture, are entirely beneficial, the bugs are... more uneven.
The bugs - which, to clarify, make up the order Hemiptera and absolutely nothing else, please*, are a a much more mixed bag. The vast majority are still utterly uninterested in your crops, but the tiny minority that do notice your crops, well....
Mostly they eat them.
There are families of true bugs that I can point to and say "look! They're GOOD for your garden!" but the family that that is most true of also includes a few blood-feeders and even one that spreads a really nasty way to die...
There are families of true bugs that I can point to and say "look! They're GOOD for your garden!" but the family that that is most true of also includes a few blood-feeders and even one that spreads a really nasty way to die...
So that's what I mean by a mixed bag.
Let's dive in, then, to a less mixed branch. Here's a picture to get you started:
So the exact number of families in the superfamily (note the ending of Pentatom"oidea" - at least in animals, this ending usually means that we're looking at a superfamily. Not always, because taxonomists as a body get bored of following their own rules rather quickly; a classic example of this would be the whole Acacia debacle**) is a bit murky. This is not because which species belong in this superfamily are difficult to work out, but because there is the usual constant disagreement between lumpers and splitters, and until taxonomic levels are cleanly defined (i.e. never), this disagreement is not going to be resolved.
Happily, however, both David Rider's Pentatomoidea catalog and the Tree of Life give the same number of families.
Oh, wait, they don't. So I'll do what I usually do when two sources I respect disagree, and move swiftly on.
In the area that I am mostly interested in (Zambia), Robertson's Database lists 11 families... which correspond more-or-less to 8 of Rider's 16 families. For consistency, we'll use Rider's families from here on, although I am not going to take a position on which set is correct because I really underestimated how much reading this was going to take (I was planning to do the entire Pentatomorpha in this post and realised that I would not finish before December), and I haven't read into the taxonomy of this group in any real depth.
Let's dive in, then, to a less mixed branch. Here's a picture to get you started:
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| Atelocera notatipennis in woodland in the Kundabwika Heritage Site, Northern Province, Zambia |
So the exact number of families in the superfamily (note the ending of Pentatom"oidea" - at least in animals, this ending usually means that we're looking at a superfamily. Not always, because taxonomists as a body get bored of following their own rules rather quickly; a classic example of this would be the whole Acacia debacle**) is a bit murky. This is not because which species belong in this superfamily are difficult to work out, but because there is the usual constant disagreement between lumpers and splitters, and until taxonomic levels are cleanly defined (i.e. never), this disagreement is not going to be resolved.
Happily, however, both David Rider's Pentatomoidea catalog and the Tree of Life give the same number of families.
Oh, wait, they don't. So I'll do what I usually do when two sources I respect disagree, and move swiftly on.
In the area that I am mostly interested in (Zambia), Robertson's Database lists 11 families... which correspond more-or-less to 8 of Rider's 16 families. For consistency, we'll use Rider's families from here on, although I am not going to take a position on which set is correct because I really underestimated how much reading this was going to take (I was planning to do the entire Pentatomorpha in this post and realised that I would not finish before December), and I haven't read into the taxonomy of this group in any real depth.
Picture break? Picture break.
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| Aspavia pallidispina in farmland in Mkushi, Central Province, Zambia |
So, without further waffle, let's dive in with easily the most agriculturally relevant family:
Shield Bugs of family Pentatomidae
(Including Robertson's Graphosomidae, Phyllocephalidae and Asopidae)
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| Aspavia albidomaculata in farmland in Chongwe, Lusaka Province, Zambia |
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| Acrosternum pallidoconspersa in farmland in Chisamba, Central Province, Zambia |
So you know how top male tennis players tend
to outperform top female tennis-players most of the time, but King beat Riggs in every set? Well, Dear Farmers, I have to tell you that you will not like the Pentatomidae most of the time but - crucially - there are exceptions.
to outperform top female tennis-players most of the time, but King beat Riggs in every set? Well, Dear Farmers, I have to tell you that you will not like the Pentatomidae most of the time but - crucially - there are exceptions.
Problems:
Crop Damage: Only a handful of species are a
problem at all, but boy can they be a problem. In
Zambia, the main culprit is Nezara viridula,
which is usually a secondary pest (meaning that it only becomes destructive as a result of
pest-control measures against other species);
it's rather generalist, but is most obvious in Soy,
where it pierces beans and developing leaves and stems, and can quite drastically reduce the
productivity of a crop.
Already a secondary pest, the damage they do to
the plants - basically by pushing a built-in straw
into whichever part of the plant is the most tender and least well defended - also creates secondary problems, opening plants up
to pathogens and creating (shortlived) chemical sensitivity which can cause plant tissues to be damaged by routine sprays.
Mitigation: As this series continues, this will
sound like a stuck record, but as with all
secondary pests, the simplest way to reduce crop losses is to limit pesticide usage wherever possible.
problem at all, but boy can they be a problem. In
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| Southern Green Stinkbug, Nezara viridula, in Mpongwe, Copperbelt Province, Zambia |
which is usually a secondary pest (meaning that it only becomes destructive as a result of
pest-control measures against other species);
it's rather generalist, but is most obvious in Soy,
where it pierces beans and developing leaves and stems, and can quite drastically reduce the
productivity of a crop.
Already a secondary pest, the damage they do to
the plants - basically by pushing a built-in straw
into whichever part of the plant is the most tender and least well defended - also creates secondary problems, opening plants up
to pathogens and creating (shortlived) chemical sensitivity which can cause plant tissues to be damaged by routine sprays.
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| Aeliomorpha griseoflava in garden in Chongwe, Lusaka Province, Zambia |
sound like a stuck record, but as with all
secondary pests, the simplest way to reduce crop losses is to limit pesticide usage wherever possible.
In itself, this is not an overly helpful suggestion.
Profit in farming depends on margins which can
be whisper thin, so most farmers will already be
avoiding spraying unless they have a pest in the
crop.
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| Afrania wahlbergi in disturbed riverine vegetation in Chief Nyalugwe's Area, Eastern Province, Zambia |
But modern commercial farming is largely
derived from a temperate model (that was recognised upon its adoption to be a short-term solution that creates long problems - but that's a whinge for another day), and just as
seasons and soils take different management
in the tropics, rubrics developed in Europe (and even South Africa) aren't always a good fit in tropical farms. So, using the example of far and away the most important Pentatomid
(or Pentatomoid, for that matter) pest in
Zambia, in the most important crop it
regularly damages (Soy), let's look at your
basic concerns and the responses
most likely to avoid you ending up with a crop
of green stink bug.
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| Afrius yolofa, a predatory shieldbug, in garden in Chongwe, Lusaka Province, Zambia |
Getting Eaten By Caterpillars
Step 1: Be specific. You don't actually have to
know which caterpillars, but you do have to know what type of damage. Are you mostly seeing:
A) Damage to fully formed leaves;
B) Damage to newly formed leaves and buds or
C) small, frass-lined holes in stems and pods?
If you answered A, then congratulations, you
have a specialist. This is good. Specialists have
spent millions of years learning not to wipe their
hosts out, and their hosts have (mostly) learnt to
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| Sunflower Seed Bug, Agonoscelis versicolor in grassland in Chongwe, Lusaka Province, Zambia |
surviving losing most of its mature leaves without
yields dropping too much. If you answered B, bad
news, you have a generalist (probably boll-worm
- a top contender for most economically important
pest in Africa). If you answered C, you are in
quite serious trouble. So now that we know what
we're dealing with, let's get on to step 2.
Step 2: Look for ecosystem correction. Every
action has an equal and opposite reaction, and
every biological BOOM is naturally followed by
a BUST. This could take the form of natural
pathogens (mostly A), predators (A and B) and
parasitoids (A, B and C caterpillars).
For your specialists (A), your natural control usually
comes in the form of conspicuous, predatory insects:
look for paper wasps, potter wasps and digger wasps,
lynx spiders and corn-crickets moving in the crop,
and the closer to the middle you see them, the better.
There are also a number of predatory stinkbugs - in
Zambian crops, look for Glypsus, Dalsira and
Basicryptus, more on them in a bit - which will make
a short meal of a fat caterpillar. If the humidity goes
up - as it often does in soy season - you should also
look out for sickly or dying caterpillars: caterpillars are basically a walking banquet to most fungi, bacteria and viruses, and diseases spread fast in large populations.
Between all of these, specialist caterpillars tend to
disappear before damage becomes untenable.
action has an equal and opposite reaction, and
every biological BOOM is naturally followed by
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| Atelocera spinulosa in riverine woodland in Mutinondo Wilderness, Muchinga Province, Zambia |
pathogens (mostly A), predators (A and B) and
parasitoids (A, B and C caterpillars).
For your specialists (A), your natural control usually
comes in the form of conspicuous, predatory insects:
look for paper wasps, potter wasps and digger wasps,
lynx spiders and corn-crickets moving in the crop,
and the closer to the middle you see them, the better.
There are also a number of predatory stinkbugs - in
Zambian crops, look for Glypsus, Dalsira and
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| Basicryptus costalis in grassland in Chongwe, Lusaka Province, Zambia |
a short meal of a fat caterpillar. If the humidity goes
up - as it often does in soy season - you should also
look out for sickly or dying caterpillars: caterpillars are basically a walking banquet to most fungi, bacteria and viruses, and diseases spread fast in large populations.
Between all of these, specialist caterpillars tend to
disappear before damage becomes untenable.
For your generalists (B), look for many of the
same wasps, but particularly keep a lookout for
the lovely Enicospilus, a large, often conspicuous
parasitoid wasp that is very good at keeping
populations of Helicoverpa and Spodoptera - two
of the most common generalist caterpillar pests
you'll see - under control. You are in a bit of a
balancing act, because these pests directly impact
upon your crop productivity, but if spraying is
appropriate, these caterpillars will usually be
the instigators.
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| Basicryptus gibbosus on granite outcrop in Mutinondo Wilderness, Muchinga Province, Zambia |
For your serious trouble (C), your options are
more limited. Again you're mostly looking for
wasps. You don't really have to know which wasps,
but if you're seeing colourful, delicate types
with long "stingers", those stingers are actually
ovipositors, set up to lay eggs into hosts which are inside plants - and wasps like this do a much
better job of finding and controlling most pests
than any late-application pesticides that you should
be able to get your hands on.
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| Bolbocoris in grassland in Chongwe, Lusaka Province, Zambia |
we're going to gaze into our six-legged (or more)
crystal ball, and go to:
Step 3: Check for your consequences. As helpful
as it would be if you were, you don't have to be
psychic here. Most of the time, you're looking for
a sign that you have other pests in your crop that
could be more destructive but are already under
control. How do you do this? Look for control.
If you've got A caterpillars and don't want B
caterpillars, for example, look for bristly green
spiders in your crop - these are lynx spiders, and
if they're in good numbers (if you see 2 or more
in 10 metres of crop, those are good numbers),
then you run the risk of seeing triple the number
of caterpillars later in the life of this crop (if
spraying early) or in your next crop. If you want
to avoid getting C caterpillars in the first place,
always check for the presence of those same
long-stingered wasps; if they are in the crop, the
caterpillar is too, but it's kept at levels where you're
not seeing it by the presence of the wasp.
And - most relevant of all - look for ant beetles and
rove beetles. These little guys are generalist
egg-predators, and they are usually keeping numbers
of a whole range of insects down, including, importantly,
the Green Stink Bug, Nezara viridula.
as it would be if you were, you don't have to be
psychic here. Most of the time, you're looking for
a sign that you have other pests in your crop that
could be more destructive but are already under
control. How do you do this? Look for control.
If you've got A caterpillars and don't want B
caterpillars, for example, look for bristly green
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| Dalsira affinis in garden in Chongwe, Lusaka Province, Zambia |
if they're in good numbers (if you see 2 or more
in 10 metres of crop, those are good numbers),
then you run the risk of seeing triple the number
of caterpillars later in the life of this crop (if
spraying early) or in your next crop. If you want
to avoid getting C caterpillars in the first place,
always check for the presence of those same
long-stingered wasps; if they are in the crop, the
caterpillar is too, but it's kept at levels where you're
not seeing it by the presence of the wasp.
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| Carbula trisignata in garden in Chongwe, Lusaka Province, Zambia |
rove beetles. These little guys are generalist
egg-predators, and they are usually keeping numbers
of a whole range of insects down, including, importantly,
the Green Stink Bug, Nezara viridula.
While your friendly, neighbourhood agrochemical
depot will often market their products as specifically
targeting pests without affecting beneficial insects,
the reality is that - at least in terms of chemicals
available in Africa - the level of specificity is "affects
invertebrates more than it affects vertebrates".
depot will often market their products as specifically
targeting pests without affecting beneficial insects,
the reality is that - at least in terms of chemicals
available in Africa - the level of specificity is "affects
invertebrates more than it affects vertebrates".
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| Delegorguella in grassland, in Chongwe, Lusaka Province, Zambia. |
What this means is that as soon as you go out
with a sprayer, you have to assume that you are
wiping out all of those predators, and it is
important to know what effects
that will have - basically, what are those predators
controlling, and will the secondary pests that rise
up in their absence be worse than the pests that
you're controlling for?
with a sprayer, you have to assume that you are
wiping out all of those predators, and it is
important to know what effects
that will have - basically, what are those predators
controlling, and will the secondary pests that rise
up in their absence be worse than the pests that
you're controlling for?
Incidentally, there is another consequence to look out for.
Hopefully, we can go into it when we get onto the Noctuoid
moths (NOT a chapter I am looking forward to), but your
pests may not be wholly detrimental to your crop: if you
have a heavy spray regime already in place, before you spray,
please take a walk in your crop and note down what insects
you most commonly see visiting the flowers. In an alarming
number of crops, I've seen the moth Helicoverpa armigera
doing the heavy lifting where it comes to pollinating - simply
because everything else is gone. Inevitably, these moths will
lay eggs whose caterpillars will consume some of the
developing pods - but effectively controlling the moths would
also prevent most of those pods from forming in the first place.
Hopefully, we can go into it when we get onto the Noctuoid
moths (NOT a chapter I am looking forward to), but your
pests may not be wholly detrimental to your crop: if you
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| Diploxys cf. fallax in the Mutinondo Wilderness Area, Muchinga Province, Zambia |
please take a walk in your crop and note down what insects
you most commonly see visiting the flowers. In an alarming
number of crops, I've seen the moth Helicoverpa armigera
doing the heavy lifting where it comes to pollinating - simply
because everything else is gone. Inevitably, these moths will
lay eggs whose caterpillars will consume some of the
developing pods - but effectively controlling the moths would
also prevent most of those pods from forming in the first place.
Which brings you to Step 4: Cost Benefit
Analysis. While every farm is different, for the
most part, the (low) financial cost of controlling
caterpillars of type A is higher than the cost of
the damage they inflict, as are often the costs of
controlling the more destructive caterpillars of
type C. Also bear in mind that costs may not be
limited to a single crop. If you are on an isolated
farm where each field is surrounded by untouched
forest, most beneficial insects will recover, at least
partially, by the next season. If, on the other hand,
your farm is surrounded by other farms, every
acre to the horizon under intense annual cultivation,
you could wait years for most predatory and parasitic
insects to recolonize.
Analysis. While every farm is different, for the
most part, the (low) financial cost of controlling
caterpillars of type A is higher than the cost of
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| Durmia capreola in orchard in Chongwe, Lusaka, Zambia |
controlling the more destructive caterpillars of
type C. Also bear in mind that costs may not be
limited to a single crop. If you are on an isolated
farm where each field is surrounded by untouched
forest, most beneficial insects will recover, at least
partially, by the next season. If, on the other hand,
your farm is surrounded by other farms, every
acre to the horizon under intense annual cultivation,
you could wait years for most predatory and parasitic
insects to recolonize.
Another future cost of spraying is the dreaded
resistance. Unless you're in the middle of a farming
block (or most of Europe, which is basically one big
farming block with occasional dwindling patches of
forest), most insect pests will show up on your farm
with nothing but a can-do attitude and their baseline
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| Durmia lutulenta in riverine vegetation in the Mutinondo Wilderness Area, Muchinga, Zambia |
Nous devons parler
de
La Resistance
Listen very carefully - I will say this only once.
(That's not true, but I couldn't resist a little 'Allo 'Allo! reference)
Resistance is what it says on the tin: how well
or how poorly a species resists any attempt to
control it. If we're going to be trying to slaughter
a living population en-masse, we should probably
try to get a little bit of empathy going for them,
so we'll use an analogy of humans, not stink-bugs,
but because I can see that people would think it
more than a little flippant if I, um, flipped the
popular analogy of comparing genocide to pest
control, we'll try to present them as victims of a
war-of-the-worlds situation rather
than a Zimbabwe*** / Tasmania / U.S.A. / New Zealand /
Australia / U.S.A. / Russia / Argentina / South Africa*** /
Brazil / Namibia / Turkey / Turkey / Turkey / Russia / Russia /
Libya / Kazakhstan / Ukraine / Poland / Latvia / Poland /
Germany / Croatia / Croatia / Poland / Russia / Guatemala /
Bangladesh / Burundi / Cambodia / Timor-Leste / Bangladesh /
Iraq / Zimbabwe*** / Somalia / Bosnia and Herzegovina /
Burundi / Rwanda / D.R.C. / Sudan / Iraq / Myanmar et al**** situation.
In this analogy, our heroes, Jack and Jill, are up a
hill when an Alien Spaceship arrives. Jill climbs
a rope down the well, while Jack stares in
astonishment at the pretty lights. When the aliens
drop a firebomb, Jack is incinerated, while Jill,
halfway down the well, gets away with mild burns.
Jill is showing behavioural resistance. When
the fires die down and she climbs back up, she
will presumably find some other quick-thinkers,
eventually have children, and teach her children
the importance of hiding from aliens with firebombs,
so that they will also (at least mostly) show
behavioural resistance.
Forty years later, let's say the aliens come back and,
when their firebombing proves ineffective, spray
all inhabited areas with aerosolized peanut butter.
Anyone allergic (Epi-pens were all burnt in the
firebombing, sorry) is toast, but the rest of the
population is probably just perplexed, and show
chemical resistance: they are physically immune to
this particular attack; and although allergies are far
from perfectly hereditary, if the aliens try again a
generation later, they will probably find that it is even less effective.
In this example, our misguided alien would-be overlords
are attacking the entire planet, Independence Day style,
so each new generation of Jill's descendants is descended
exclusively from survivors of a previous invasion.
Now imagine that the aliens are only interested in, say,
Kentucky, which just happens to be where Jack and Jill
start out.
Now, when Jill emerges from her well, she might join
with other survivors of the state-wide firebombing, or
she might walk through the burnt husk of her state and
into Tennessee, where she meets and falls in love with
Bob. Bob lives in a boring little flat in the city, and
when the Aliens don't seem to be coming back, Jill and
Bob move to Jill's farm and set up shop. Jill tries to
instill the importance of hiding from spaceships in her
children's minds, but Bob isn't entirely certain that it
really happened, so when the pretty lights appear in the
sky again, only a few of the now adult children remember
Jill's advice and scramble down the wells, and, like Jill,
any survivors might choose to marry people who come
from outside state lines, even if they re-settle Kentucky
in the end (if you think that people wouldn't be so
foolish as to live in a place where aliens invade every
forty years, bear in mind that plenty of humans around
the world live on flood-plains and in hurricane zones
and on active volcanoes). The result is that, although the population of Kentucky is regularly under selection
pressure for resistance, the genes coding chemical and
behavioural resistance are rather unlikely to get fixed,
because there are more potential husbands and wives
from out-of-state than in-state, and so there is a constant
in-flow of naïve genetics into Jill's family tree.
In case this seems irrelevant, read "Kentucky"
as your field. The point here is to demonstrate that
the rate at which a pest population develops resistance
is slower in populations that are not all placed under
the same pressure. Jill Mk I, living in a world reduced
to peanut-buttery ash by aliens, is a stink-bug living
in the middle of an intense, no-acre-spared, commercial
farming block. Jill Mk II is instead living on a field
surrounded by woodland. From the farmer's perspective,
Jill Mk II and her descendants are much easier to control,
while Jill Mk I's grandchildren will eventually reach such
numbers that the 40-year aliens give up on farming earth
entirely, and try to set up their weird blood-weed farm on
Mars instead.
So now that we're through with that slightly disturbing
little analogy, you hopefully have a nice little checklist
to go through next time you think about spraying, and
we can move on to:
Benefits (No, Really, We're STILL doing the
farming thing)
I thought about doing another problem, vis-a-vis their capacity to spray a liquid with
the approximate smell of rotten coriander at potential threats, but after we've put
ourselves into the shoes of the War-of-the-Worlds alien trying to wipe out Jill and her
descendants, that seems a little bit too trivial to mention in full size font.
Caterpillar Control: It's worth noting at this point
that this is usually different species to the stinkbugs
that can become a pest when you spray to control
caterpillars, but in addition to genera such as
Dalsira and Basicryptus, the entirety of the
subfamily Asopinae is composed of predators
of caterpillars(and other soft-bodied prey).
They're not usually as
voracious as some predators, such as Lynx spiders
(Aranae: Oxyopidae), but they're also a lot better at
not eating each other than most spiders, so they can
sometimes reach high densities in the environment.
Predator/Parasite Reservoir: This is one of those
benefits that seems like a cop-out, but is much more
important than most people realise and/or
acknowledge. If you're managing your farm in a
population-dynamics conscious manner, and doing
everything that you can do to ensure that your farm
does as little as possible to disrupt local ecology, you
will still have (hopefully rare) pest outbreaks. This
would even be true if you were farming on, say, a
desert island or some sort of experimental Russian
agricultural space-farm: whether it's your neighbour's
overindulgence on carbamates creating an outbreak of
fall armyworm, El Niño on climate-change steroids
creating a series of drought years leading to an explosion
in locust populations in the western grasslands, or just
a weird smear on Svetlana's boot that ends up turning
your thriving space-tomatoes into a soggy pile of
космический компост.
In all of these situations, how much of a crop you can
recover depends in no small way on the speed with
which you can begin to defend your crop. In your very
best case scenario, you would start responding before
you noticed the problem.
No, you don't need time-travel to do this.
What you need is a healthy population of natural
predators and parasites.
Seeing as we realised at some point after we wiped out
the dodo that God doesn't just 'pop' animals into
existence whenever we might have need of them, I'm
sure that we can all agree that your predators and
parasites are going to need to have a good reason to be
in any given area - which means that they need to eat.
Now, obviously, the beneficials that you most want to
attract are the ones that are most likely to eat (inside
or out) your most important pests, but despite the benefits of retaining a control-
naive population, it's a rare farmer who can
be convinced to maintain a healthy population
of his bitterest enemies just to ensure that their
bitterest enemies are well fed. The next best
thing is to maintain the closest non-pest
relatives to your pests, as close as possible
to your fields - while some parasitoids are very
specific, most have a narrow range of hosts - such as a
pest species and seven or eight related, non-pest species.
This is not going to be the last time that I say this, but this is why uncultivated
margins matter. These provide a crucial
environment for hundreds of species
that have no interest whatsoever in your
crop (and yes, a handful of species that do
have an interest in your crop), which in
turn can support dozens of species that
directly benefit your crop, primarily
through predation and pollination.
For reasons that are hopefully obvious, these
beneficial animals are more valuable if there are
more of them. I'm not saying going out and buy
a bunch of ladybirds (please don't - the consequences
can be disastrous if it's the wrong ladybird), I'm
saying that you want to start thinking about thickets.
Thickets - the dense, often impenetrable habitat that
forms as a transition between open, grassy habitats
and canopied forest or woodland - are an incredibly
rich environment that can support a fantastic diversity
of invertebrates and other small animals, and of all
the natural habitats you should seek to provide on
your farm, thickets are the ones that will serve you best.
But what's this I hear you say? My thickets are all gone,
or too far from my crop to provide a convenient living
arrangement for beneficial predators and pollinators?
Three words.
Plant.
A.
Hedge.
By which, I must be clear, I do not mean a topiary
boundary. I mean a hedge. It doesn't have to be native
species; it can be fruit bushes or ornamental species
(unless they are allelopaths, like Lantana camara,
which stunt and kill the plants around them - try to
avoid those) - and then don't discourage the assortment
of native vines and trees that do move in, just trim them
back every year or two, to keep any of the component
species from excluding the rest.
It has been said before, and I will certainly say it again,
but Hedges are wonderful. They are a DIY thicket,
give a huge boost to a vast range of wildlife species, and they allow you to bound your entire
crop with humming apartment blocks for
your beneficials - for instant access and
rapid-response control. They also help to
reduce erosion and moisture loss in the
immediate area, and a diverse mix of
different trees and shrubs creates a nutrient-
rich mulch, which boosts fertility in adjacent
crops. In the dense agricultural landscape of
Britain's 1600s to 1800s, they were a staple of
actually keeping the land productive, and they
are one of the (fairly few) aspects of European
agriculture that are readily transferable to
other climates and soil types; arguably, because our insect populations don't have
the same annual reset as is found in much
of Europe, they are more effective in
countries like Zambia than they are in
cold-temperate regions.
For farmers who rely primarily on large machinery and automation, installation of hedgerows is limited to the margins of large fields, which does limit their capacity to control pests. For smaller farmers, the fertility boost that the surrounding crop receives more than compensates for the cropping area lost by breaking up larger fields with a hedge or twenty. Treat 6 metres as its maximum height - and, bearing in mind that lower hedges have a reduced "reach" in terms of limiting erosion, wind damage and water loss, you can go as low as 1m and still give a massive boost to your beneficial insects.
Plant hedges. For you, for your crop, for the insects, the climate and all our futures. They are excellent.
Anyway, where was I?
Oh, yes. Stink bugs.
So, we've done the big one; the rest will be quick.
One half of the above statement is true. It's the first bit.
Let's get it over with: These are not ladybirds, or
ladybugs or ladybeetles (and all those things are
beetles, anyhow).
If in doubt, look closer: ladybirds - like most beetles -
have a distinct seam where their hardened forewings
meet; in Scutellerids, their wings are entirely or
almost covered by their massively expanded
scutellum, so no seam. The ladybirds - as beetles -
also have fairly standard mandibles, while
Scutellerids, as bugs, have a bug-standard rostrum -
essentially a drinking straw - which is tucked neatly
under their bodies when not in use.
So where do they figure in agriculture?
Well:
Problems: Less than above. Well, less species, at least.
While the overwhelming majority are completely
uninterested in your crop, a couple of species can be
more problematic - and at the top of that list are the
very pretty "rainbow shield bugs", Calidea.
Calidea, particularly the common Calidea dregii, are
rather polyphagous - a trait that is shared with
Nezara viridula, the most important African pest out of all the many species of
Pentatomoidea. They and other
Scutellerids are generally considered
lesser pests for two main reasons: First,
their generation times can often be longer***** and produce smaller
generations, so populations expand
rather than explode, and their hosts do
not include Zambia's most
economically important row crops.
That is not to say that do not affect important crops - cotton, sunflowers,
cassava, sorghum, cashew nuts,
Jatropha and Macadamias are just a
handful of the crops that they can and do
feed on, and while most farmers these days
have entirely lost interest in Jatropha as a
crop, many of this species' hosts are
important either as local staples or as
smaller-scale commercial ventures.
A common feature of most Hemipteran crop pests -
whether we're talking Aphids or Shield bugs - is that
they tend to be secondary pests. Because the crops that
Calidea feeds on tend not to be subjected to such heavy
pesticide regimes, they also do not tend to suffer such
heavy infestations of secondary pests, and
chemical control is not usually viable.
But perhaps the most important factor limiting the
importance of this species as a crop pest is that Adults
and nymphs cannibalize eggs.
As monstrous as this might seem, it makes pretty good evolutionary sense: All life-stages in this species feed
in the same way on the same host plants, so young and
adults inevitably compete. When there are abundant
adults around, newly hatched nymphs will reduce fitness of adults through competition, and most likely die - wasting resources. Opportunistic cannibalism of eggs ensures that this competition does not happen as often, and that hatching only occurs following a die-off of adults, such as after a period of heavy storms (or pesticide application), and so the nymphs are not competing with their parents for the same resources.
Benefits:
Beyond Calidea's cannibalistic self-regulation, direct benefits to the crop are few - but, as with everything else, the non-pest species add valuable diversity and resulting stability to ecosystems, helping to ensure that your directly beneficial species are there when you need them.
An effect - and you can decide for yourselves whether it is beneficial or not - is that by feeding on the young stems of woody plants, they can often weaken or kill the growing point - which helps to stimulate branching. Many sap-sucking bugs have this type of effect on plants, and few wild plants seem to be particularly harmed by this.
When it comes to the pill-bugs, there really isn't much to say other than "they're quite neat-looking". They can be fairly common - but I've never encountered them at anywhere near plague proportions, and they generally don't show much interest in crop species.
In terms of life history they are much like the
Scutelleridae, but - at least regionally - they tend to
be smaller, rather short-bodied and rather less showy.
If the phylogeny of Lis et al. (2017) is correct, they
may have a more interesting backstory than I usually
give them credit for - they are descended from within
the paraphyletic assemblage that we all (?) know as
the Cydnidae, inviting speculation (mine) that they
were more like modern Cydnids in their past, and
have arrived at a similar form and lifestyle to the
Scutellerids by an independent route, rather than
simply being an early offshoot from the Scutelleridae.
While we are in the mostly-agriculturally-irrelevant section of the superfamily at this point, the Cydnidae are probably the least irrelevant of
these. The vast majority of them have no interest in any crops, but they can still have....
Problems:
Direct Feeding on Crop Roots.
This is mostly a New World problem, but to avoid seeming like I support nationalist philosophies, I'll briefly mention them here: least controversially, Cyrtomenus bergi feeds on the roots of cassava. The main problem this causes is aesthetic: most of the time, the damage is limited to a fairly shallow brownish spot on the cassava, without reducing yield or edibility, but these puncture wounds can open the plant up to infection
by various pathogens - although that is rare.
The more controversial "pests" are the various species of Scaptocoris, which can feed on the roots of various different crops - but more on them under benefits.
Incidental damage
In most of the world, if you have a problem with Burrowing
Bugs, this is it: they move around in the soil. Plants roots are
in the soil. They do not necessarily show all the due care and
attention when moving past your plants roots that you might
like, and sometimes their movements cause physical damage.
In most settings, this does not actually cause any real harm: plants have actually spent less time on land than small burrowing animals, and as such are quite used to occasionally having to regrow a bit of root. However, soils under heavy agriculture tend to be both more waterlogged and more compacted than the soils that the crops wild ancestors would have preferred, with the result that both burrowing insects and plants' roots are concentrated in a greatly reduced area of habitable, aerobic topsoil - so
damage is higher than it might be in a natural system.
Unless your soil is very compacted and your
Burrowing Bug numbers very high (unlikely - see
below), most crops absorb this damage without
any apparent drop in yield.
So now we have to talk about:
Benefits:
Soil Aeration:
Agricultural soils tend to compact over time; even in zero-til situations - rain falling on bare soil leads to a fair amount of compaction, even without heavy machinery.
Fortunately, the world in general - and African soils in particular - are used to a fairly good analogue of heavy machinery: large vertebrates have been trampling over land surfaces, especially in fertile plains that lend themselves to agriculture, for somewhere in the region of 300 million years. The periodic dips in abundance probably aren't the reason that Africa's ancient soils haven't compacted into rock by now. Instead, the saviours of agriculture come in the form of animals that (mostly) inhabit the opposite end of the scale: worms, beetles, grubs and burrowing bugs create openings in soil as they go about their daily lives, allowing air and water into places it couldn't usually go, and creating a dynamic environment for the roots, plant stems and fungal communities that should be the backbone of any long-term fertile soil.
This beneficial effect isn't limited to invertebrates: I plant agapanthus and cordylines in the full expectation that most of them will be eaten from the bottom up by Ansell's mole-rats, an endemic eusocial mammal whose ceaseless burrowing is an easy improvement for drainage and decreases erosion through run-off - but in most crops, larger animals are going to cause considerable headaches, and mole-rats in particular aren't going to be in your crop if they can't eat it, and they can eat a lot. So burrowing bugs are a lot more convenient.
Crop Protection:
So this section may be irrelevant to African species, as to my knowledge it has only been demonstrated for the
American Scaptocoris - but it may be considerably less than irrelevant: as with most members of the Pentatomorpha, the Cydnidae
possess stink glands (Hence "Stink Bugs"...) and out of these small and inconspicuous chemical factories, some Scaptocoris are known to produce natural 'cides - which in the case of Scaptocoris talpa at
sufficient densities, can protect tomato seedlings and
bananas from pathogenic fungi and nematodes - although
the densities used in the study were to my mind rather
high, bananas in particular are incredibly prone to fungal
infections, so anything that could reduce the need for expensive
chemical protection is worth looking into.
Although this is very firmly a small family, they are - at least regionally - far from irrelevant. Over Zambia they tend not to reach particularly high densities, presumably because our woodlands don't favour their favourite host plants, but in various communities in South Africa, the edibility and seasonal abundance of these little guys makes them a valuable foodstuff. There's more about that in my post dedicated to still-the-only-one-I've-met-in-Zambia, Natalicola pallida (Westwood, 1837)
Agriculturally, though, they pretty much irrelevant except for enhancing diversity and thereby stability of the hedgerows and marginal woodland that you have surely decided to plant if you've reached this far down in a post that is already leviathan (and I'm saying that before I've even added pictures).
Whoever said that the small families are of no economic importance?
Problems:Eating Your Cucurbits
If you live in Africa, and are growing crops of the family Cucurbitaceae - the family of cucumbers, watermelons, squashes and gourds - you have probably met this family. They are not all pests (of course) but several species of Coridius, probably the most successful genus regionally, do have an unfortunate habit of feeding on watermelons and pumpkins, which any drive along Zambia's major roads will show you are very important crops locally, and Coridius also feed on various other regionally popular vegetables.
Although they tend to fall victim to a similar range of predators and natural controls as species such as Nezara, populations of specialist pests are rather easier to manage through planting habits: by limiting the continuous area of suitable host plants - i.e. separating small fields of crops by hedges or set-aside, and using mixed-planting and intercropping to their full potential - you can keep most specialist pests from ever reaching numbers where control is necessary or makes any economic sense.
The Other Shield Bugs of family Acanthosomatidae
The Acanthosomatidae are usually treated as rather basal within the Pentatomoidea. Like the Plataspididae, they are offered a move to new and exotic locations by Lis et al, 2017, who indicate that they are rather closely related to the Cydnidae - more closely related, in fact, than some of the other Cydnidae. This is not nearly so well supported by Lis et al's data as the nesting of the Parastrachiidae into a subfamily of the Cydnidae, and the higher-level taxonomy of the superfamily is rather weakly resolved by their study, so - as with the Plataspididae - I am continuing to treat them as separate family.
A single species probably enters Zambia, the widespread Uhlunga typica, which turns up all over sub-saharan Africa, but I've not yet met it. You're probably not going to find them in your crops - any crops, but if you do, they are almost certainly there by accident.
In case you can't guess from the "probably", I have not yet met Uhlunga, and can't show you a picture.
Sorry.
Here's a European one instead.
And - well, it seems like that's all, folks?
(That's not true, but I couldn't resist a little 'Allo 'Allo! reference)
 |
| Erachteus lutulentus in streamside vegetation in Mafinga Hills, Muchinga Province, Zambia |
Resistance is what it says on the tin: how well
or how poorly a species resists any attempt to
control it. If we're going to be trying to slaughter
a living population en-masse, we should probably
try to get a little bit of empathy going for them,
so we'll use an analogy of humans, not stink-bugs,
but because I can see that people would think it
more than a little flippant if I, um, flipped the
popular analogy of comparing genocide to pest
control, we'll try to present them as victims of a
 |
| Glypsus, a predatory shieldbug, in cropland in Chisamba, Central Province, Zambia |
than a Zimbabwe*** / Tasmania / U.S.A. / New Zealand /
Australia / U.S.A. / Russia / Argentina / South Africa*** /
Brazil / Namibia / Turkey / Turkey / Turkey / Russia / Russia /
Libya / Kazakhstan / Ukraine / Poland / Latvia / Poland /
Germany / Croatia / Croatia / Poland / Russia / Guatemala /
Bangladesh / Burundi / Cambodia / Timor-Leste / Bangladesh /
Iraq / Zimbabwe*** / Somalia / Bosnia and Herzegovina /
Burundi / Rwanda / D.R.C. / Sudan / Iraq / Myanmar et al**** situation.
In this analogy, our heroes, Jack and Jill, are up a
hill when an Alien Spaceship arrives. Jill climbs
a rope down the well, while Jack stares in
astonishment at the pretty lights. When the aliens
drop a firebomb, Jack is incinerated, while Jill,
halfway down the well, gets away with mild burns.
Jill is showing behavioural resistance. When
the fires die down and she climbs back up, she
will presumably find some other quick-thinkers,
 |
| Sciocoris in garden in Chongwe, Lusaka Province, Zambia |
the importance of hiding from aliens with firebombs,
so that they will also (at least mostly) show
behavioural resistance.
Forty years later, let's say the aliens come back and,
when their firebombing proves ineffective, spray
all inhabited areas with aerosolized peanut butter.
Anyone allergic (Epi-pens were all burnt in the
firebombing, sorry) is toast, but the rest of the
population is probably just perplexed, and show
chemical resistance: they are physically immune to
 |
| Sepontia misella in orchard in Chongwe, Luzaka, Zambia |
from perfectly hereditary, if the aliens try again a
generation later, they will probably find that it is even less effective.
In this example, our misguided alien would-be overlords
are attacking the entire planet, Independence Day style,
so each new generation of Jill's descendants is descended
exclusively from survivors of a previous invasion.
Now imagine that the aliens are only interested in, say,
Kentucky, which just happens to be where Jack and Jill
start out.
 |
| Veterna sanguineirostris in garden in Chongwe, Lusaka Province, Zambia' |
Now, when Jill emerges from her well, she might join
with other survivors of the state-wide firebombing, or
she might walk through the burnt husk of her state and
into Tennessee, where she meets and falls in love with
Bob. Bob lives in a boring little flat in the city, and
when the Aliens don't seem to be coming back, Jill and
Bob move to Jill's farm and set up shop. Jill tries to
instill the importance of hiding from spaceships in her
children's minds, but Bob isn't entirely certain that it
really happened, so when the pretty lights appear in the
 |
| Stenozygum in cropland in Kafue Town, Lusaka Province, Zambia |
Jill's advice and scramble down the wells, and, like Jill,
any survivors might choose to marry people who come
from outside state lines, even if they re-settle Kentucky
in the end (if you think that people wouldn't be so
foolish as to live in a place where aliens invade every
forty years, bear in mind that plenty of humans around
the world live on flood-plains and in hurricane zones
and on active volcanoes). The result is that, although the population of Kentucky is regularly under selection
pressure for resistance, the genes coding chemical and
behavioural resistance are rather unlikely to get fixed,
because there are more potential husbands and wives
from out-of-state than in-state, and so there is a constant
in-flow of naïve genetics into Jill's family tree.
In case this seems irrelevant, read "Kentucky"
as your field. The point here is to demonstrate that
the rate at which a pest population develops resistance
 |
| Eurydema ornata in roadside ditch near Hündeleskopf, Bavaria, Germany |
the same pressure. Jill Mk I, living in a world reduced
to peanut-buttery ash by aliens, is a stink-bug living
in the middle of an intense, no-acre-spared, commercial
farming block. Jill Mk II is instead living on a field
surrounded by woodland. From the farmer's perspective,
Jill Mk II and her descendants are much easier to control,
while Jill Mk I's grandchildren will eventually reach such
numbers that the 40-year aliens give up on farming earth
entirely, and try to set up their weird blood-weed farm on
Mars instead.
So now that we're through with that slightly disturbing
little analogy, you hopefully have a nice little checklist
to go through next time you think about spraying, and
we can move on to:
 |
| Lerida punctata in cliffside vegetation in the Kundabwika Heritage Area, Northern Province, Zambia |
 |
| Macrorhaphis acuta, a predatory stinkbug in garden in Chongwe, Lusaka Province, Zambia |
farming thing)
I thought about doing another problem, vis-a-vis their capacity to spray a liquid with
the approximate smell of rotten coriander at potential threats, but after we've put
ourselves into the shoes of the War-of-the-Worlds alien trying to wipe out Jill and her
descendants, that seems a little bit too trivial to mention in full size font.
Caterpillar Control: It's worth noting at this point
that this is usually different species to the stinkbugs
that can become a pest when you spray to control
caterpillars, but in addition to genera such as
Dalsira and Basicryptus, the entirety of the
subfamily Asopinae is composed of predators
of caterpillars(and other soft-bodied prey).
They're not usually as
 |
| Menida dubia in riverine thicket in Mutinondo Wilderness Area, Zambia |
(Aranae: Oxyopidae), but they're also a lot better at
not eating each other than most spiders, so they can
sometimes reach high densities in the environment.
Predator/Parasite Reservoir: This is one of those
benefits that seems like a cop-out, but is much more
important than most people realise and/or
acknowledge. If you're managing your farm in a
population-dynamics conscious manner, and doing
everything that you can do to ensure that your farm
does as little as possible to disrupt local ecology, you
 |
| Green Shieldbug, Palomena prasina, in Bosham, West Sussex, England |
would even be true if you were farming on, say, a
desert island or some sort of experimental Russian
agricultural space-farm: whether it's your neighbour's
overindulgence on carbamates creating an outbreak of
fall armyworm, El Niño on climate-change steroids
creating a series of drought years leading to an explosion
in locust populations in the western grasslands, or just
a weird smear on Svetlana's boot that ends up turning
your thriving space-tomatoes into a soggy pile of
космический компост.
 |
| Parantestia cincticollis (red morph) in garden in Chongwe, Lusaka Province, Zambia |
In all of these situations, how much of a crop you can
recover depends in no small way on the speed with
which you can begin to defend your crop. In your very
best case scenario, you would start responding before
you noticed the problem.
No, you don't need time-travel to do this.
What you need is a healthy population of natural
predators and parasites.
Seeing as we realised at some point after we wiped out
the dodo that God doesn't just 'pop' animals into
existence whenever we might have need of them, I'm
sure that we can all agree that your predators and
parasites are going to need to have a good reason to be
 |
| Red-Legged Shield-Bug, Pentatoma rufipes on roadside in Fishbourne, West Sussex, England |
Now, obviously, the beneficials that you most want to
attract are the ones that are most likely to eat (inside
or out) your most important pests, but despite the benefits of retaining a control-
naive population, it's a rare farmer who can
be convinced to maintain a healthy population
of his bitterest enemies just to ensure that their
bitterest enemies are well fed. The next best
thing is to maintain the closest non-pest
relatives to your pests, as close as possible
to your fields - while some parasitoids are very
specific, most have a narrow range of hosts - such as a
pest species and seven or eight related, non-pest species.
 |
| Spiny Shieldbug, Picromerus bidens (predatory) in downland meadow in Kingley Vale, West Sussex, England. |
margins matter. These provide a crucial
environment for hundreds of species
that have no interest whatsoever in your
crop (and yes, a handful of species that do
have an interest in your crop), which in
turn can support dozens of species that
directly benefit your crop, primarily
through predation and pollination.
For reasons that are hopefully obvious, these
beneficial animals are more valuable if there are
more of them. I'm not saying going out and buy
 |
| Piezodorus purus in garden in Chongwe, Lusaka Province, Zambia |
can be disastrous if it's the wrong ladybird), I'm
saying that you want to start thinking about thickets.
Thickets - the dense, often impenetrable habitat that
forms as a transition between open, grassy habitats
and canopied forest or woodland - are an incredibly
rich environment that can support a fantastic diversity
of invertebrates and other small animals, and of all
the natural habitats you should seek to provide on
your farm, thickets are the ones that will serve you best.
 |
| Pseudatelus natalensis, in grassland in Chongwe, Lusaka Province, Zambia |
But what's this I hear you say? My thickets are all gone,
or too far from my crop to provide a convenient living
arrangement for beneficial predators and pollinators?
Three words.
Plant.
A.
 |
| Bronze Shieldbug, Troilus luridus, in woodland at Kingley Vale, West Sussex, England |
By which, I must be clear, I do not mean a topiary
boundary. I mean a hedge. It doesn't have to be native
species; it can be fruit bushes or ornamental species
(unless they are allelopaths, like Lantana camara,
which stunt and kill the plants around them - try to
avoid those) - and then don't discourage the assortment
of native vines and trees that do move in, just trim them
back every year or two, to keep any of the component
species from excluding the rest.
 |
| Tyoma cryptorhyncha in grassland in Chongwe, Lusaka Province, Zambia. |
but Hedges are wonderful. They are a DIY thicket,
give a huge boost to a vast range of wildlife species, and they allow you to bound your entire
crop with humming apartment blocks for
your beneficials - for instant access and
rapid-response control. They also help to
reduce erosion and moisture loss in the
immediate area, and a diverse mix of
different trees and shrubs creates a nutrient-
rich mulch, which boosts fertility in adjacent
crops. In the dense agricultural landscape of
Britain's 1600s to 1800s, they were a staple of
actually keeping the land productive, and they
are one of the (fairly few) aspects of European
agriculture that are readily transferable to
other climates and soil types; arguably, because our insect populations don't have
the same annual reset as is found in much
of Europe, they are more effective in
countries like Zambia than they are in
cold-temperate regions.
For farmers who rely primarily on large machinery and automation, installation of hedgerows is limited to the margins of large fields, which does limit their capacity to control pests. For smaller farmers, the fertility boost that the surrounding crop receives more than compensates for the cropping area lost by breaking up larger fields with a hedge or twenty. Treat 6 metres as its maximum height - and, bearing in mind that lower hedges have a reduced "reach" in terms of limiting erosion, wind damage and water loss, you can go as low as 1m and still give a massive boost to your beneficial insects.
Plant hedges. For you, for your crop, for the insects, the climate and all our futures. They are excellent.
Anyway, where was I?
Oh, yes. Stink bugs.
So, we've done the big one; the rest will be quick.
One half of the above statement is true. It's the first bit.
 |
| Platacantha lutea in riverine vegetation on the lower Zambezi, Lusaka Province, Zambia. |
Shield-Backed Bugs of family Scutelleridae
 |
| Rainbow Shieldbug, Calidea dregii, in scrub in Chongwe, Lusaka Province, Zambia |
 |
| Hotea subfasciata in garden in Chongwe, Lusaka Province., Zambia |
Let's get it over with: These are not ladybirds, or
ladybugs or ladybeetles (and all those things are
beetles, anyhow).
If in doubt, look closer: ladybirds - like most beetles -
have a distinct seam where their hardened forewings
meet; in Scutellerids, their wings are entirely or
almost covered by their massively expanded
scutellum, so no seam. The ladybirds - as beetles -
also have fairly standard mandibles, while
Scutellerids, as bugs, have a bug-standard rostrum -
essentially a drinking straw - which is tucked neatly
 |
| Sphaerocoris testudogrisea in scrub in Chongwe, Lusaka Province, Zambia |
So where do they figure in agriculture?
Well:
Problems: Less than above. Well, less species, at least.
While the overwhelming majority are completely
uninterested in your crop, a couple of species can be
more problematic - and at the top of that list are the
very pretty "rainbow shield bugs", Calidea.
Calidea, particularly the common Calidea dregii, are
 |
| Picasso Bug, Sphaerocoris annulus in woodland in Kundabwika Heritage Area, Northern Province, Zambia |
Nezara viridula, the most important African pest out of all the many species of
Pentatomoidea. They and other
Scutellerids are generally considered
lesser pests for two main reasons: First,
their generation times can often be longer***** and produce smaller
generations, so populations expand
rather than explode, and their hosts do
not include Zambia's most
economically important row crops.
That is not to say that do not affect important crops - cotton, sunflowers,
cassava, sorghum, cashew nuts,
Jatropha and Macadamias are just a
handful of the crops that they can and do
feed on, and while most farmers these days
have entirely lost interest in Jatropha as a
crop, many of this species' hosts are
important either as local staples or as
smaller-scale commercial ventures.
A common feature of most Hemipteran crop pests -
 |
| Steganocerus multipunctatus in orchard in Chongwe, Lusaka Province, Zambia |
they tend to be secondary pests. Because the crops that
Calidea feeds on tend not to be subjected to such heavy
pesticide regimes, they also do not tend to suffer such
heavy infestations of secondary pests, and
chemical control is not usually viable.
But perhaps the most important factor limiting the
importance of this species as a crop pest is that Adults
and nymphs cannibalize eggs.
As monstrous as this might seem, it makes pretty good evolutionary sense: All life-stages in this species feed
 |
| Solenosthedium liligera on dung in woodland in Mutinondo Wilderness, Muchinga Province, Zambia |
adults inevitably compete. When there are abundant
adults around, newly hatched nymphs will reduce fitness of adults through competition, and most likely die - wasting resources. Opportunistic cannibalism of eggs ensures that this competition does not happen as often, and that hatching only occurs following a die-off of adults, such as after a period of heavy storms (or pesticide application), and so the nymphs are not competing with their parents for the same resources.
Benefits:
Beyond Calidea's cannibalistic self-regulation, direct benefits to the crop are few - but, as with everything else, the non-pest species add valuable diversity and resulting stability to ecosystems, helping to ensure that your directly beneficial species are there when you need them.
An effect - and you can decide for yourselves whether it is beneficial or not - is that by feeding on the young stems of woody plants, they can often weaken or kill the growing point - which helps to stimulate branching. Many sap-sucking bugs have this type of effect on plants, and few wild plants seem to be particularly harmed by this.
Pill Bugs of family Plataspididae (or Brachyplatidae)
 |
| Coptosoma affinis in riverine woodland in Chief Nyalugwe's area, Eastern Province, Zambia |
 |
| Coptosoma conspersa in riverine woodland in Kabwelume-Lumangwe Heritage Area, Northern Province, Zambia |
When it comes to the pill-bugs, there really isn't much to say other than "they're quite neat-looking". They can be fairly common - but I've never encountered them at anywhere near plague proportions, and they generally don't show much interest in crop species.
In terms of life history they are much like the
 |
| Coptosoma nubilum in grassland in Chongwe, Lusaka Province, Zambia |
be smaller, rather short-bodied and rather less showy.
If the phylogeny of Lis et al. (2017) is correct, they
may have a more interesting backstory than I usually
give them credit for - they are descended from within
the paraphyletic assemblage that we all (?) know as
the Cydnidae, inviting speculation (mine) that they
were more like modern Cydnids in their past, and
have arrived at a similar form and lifestyle to the
Scutellerids by an independent route, rather than
simply being an early offshoot from the Scutelleridae.
Burrowing Bugs of family Cydnidae
Parastrachiidae are here considered not to be a real family but a scattering of near-Sehirine Cydnids - hence inclusion of Dismegistus images. Seefor justification. By the phylogeny presented in the same paper, the Plataspididae should proably be sunk into this family, too. While we are in the mostly-agriculturally-irrelevant section of the superfamily at this point, the Cydnidae are probably the least irrelevant of
these. The vast majority of them have no interest in any crops, but they can still have....
Problems:
Direct Feeding on Crop Roots.
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| Dismegistus cf fimbriatus in riverine vegetation, Mutinondo Wilderness, Muchinga Province, Zambia |
by various pathogens - although that is rare.
The more controversial "pests" are the various species of Scaptocoris, which can feed on the roots of various different crops - but more on them under benefits.
Incidental damage
In most of the world, if you have a problem with Burrowing
Bugs, this is it: they move around in the soil. Plants roots are
in the soil. They do not necessarily show all the due care and
attention when moving past your plants roots that you might
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| Lalervis tibialis in garden in Chongwe, Lusaka, Zambia |
In most settings, this does not actually cause any real harm: plants have actually spent less time on land than small burrowing animals, and as such are quite used to occasionally having to regrow a bit of root. However, soils under heavy agriculture tend to be both more waterlogged and more compacted than the soils that the crops wild ancestors would have preferred, with the result that both burrowing insects and plants' roots are concentrated in a greatly reduced area of habitable, aerobic topsoil - so
damage is higher than it might be in a natural system.
Unless your soil is very compacted and your
Burrowing Bug numbers very high (unlikely - see
below), most crops absorb this damage without
any apparent drop in yield.
So now we have to talk about:
Benefits:
Soil Aeration:
Agricultural soils tend to compact over time; even in zero-til situations - rain falling on bare soil leads to a fair amount of compaction, even without heavy machinery.
Fortunately, the world in general - and African soils in particular - are used to a fairly good analogue of heavy machinery: large vertebrates have been trampling over land surfaces, especially in fertile plains that lend themselves to agriculture, for somewhere in the region of 300 million years. The periodic dips in abundance probably aren't the reason that Africa's ancient soils haven't compacted into rock by now. Instead, the saviours of agriculture come in the form of animals that (mostly) inhabit the opposite end of the scale: worms, beetles, grubs and burrowing bugs create openings in soil as they go about their daily lives, allowing air and water into places it couldn't usually go, and creating a dynamic environment for the roots, plant stems and fungal communities that should be the backbone of any long-term fertile soil.
This beneficial effect isn't limited to invertebrates: I plant agapanthus and cordylines in the full expectation that most of them will be eaten from the bottom up by Ansell's mole-rats, an endemic eusocial mammal whose ceaseless burrowing is an easy improvement for drainage and decreases erosion through run-off - but in most crops, larger animals are going to cause considerable headaches, and mole-rats in particular aren't going to be in your crop if they can't eat it, and they can eat a lot. So burrowing bugs are a lot more convenient.
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| Pied Shield Bug, Tritomegas bicolor, in cropland in Bosham, West Sussex, England. |
So this section may be irrelevant to African species, as to my knowledge it has only been demonstrated for the
American Scaptocoris - but it may be considerably less than irrelevant: as with most members of the Pentatomorpha, the Cydnidae
possess stink glands (Hence "Stink Bugs"...) and out of these small and inconspicuous chemical factories, some Scaptocoris are known to produce natural 'cides - which in the case of Scaptocoris talpa at
sufficient densities, can protect tomato seedlings and
bananas from pathogenic fungi and nematodes - although
the densities used in the study were to my mind rather
high, bananas in particular are incredibly prone to fungal
infections, so anything that could reduce the need for expensive
chemical protection is worth looking into.
Inflated Shield Bugs of family Tessarotomidae
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| Natalicola pallida in Garden in Chongwe, Lusaka Province, Zambia |
Although this is very firmly a small family, they are - at least regionally - far from irrelevant. Over Zambia they tend not to reach particularly high densities, presumably because our woodlands don't favour their favourite host plants, but in various communities in South Africa, the edibility and seasonal abundance of these little guys makes them a valuable foodstuff. There's more about that in my post dedicated to still-the-only-one-I've-met-in-Zambia, Natalicola pallida (Westwood, 1837)
Agriculturally, though, they pretty much irrelevant except for enhancing diversity and thereby stability of the hedgerows and marginal woodland that you have surely decided to plant if you've reached this far down in a post that is already leviathan (and I'm saying that before I've even added pictures).
Watermelon Shield Bugs of family Dinidoridae
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| Coridius in woodland in Kabwelume-Lumangwe Heritage Area, Northern Province, Zambia |
Whoever said that the small families are of no economic importance?
Problems:Eating Your Cucurbits
If you live in Africa, and are growing crops of the family Cucurbitaceae - the family of cucumbers, watermelons, squashes and gourds - you have probably met this family. They are not all pests (of course) but several species of Coridius, probably the most successful genus regionally, do have an unfortunate habit of feeding on watermelons and pumpkins, which any drive along Zambia's major roads will show you are very important crops locally, and Coridius also feed on various other regionally popular vegetables.
Although they tend to fall victim to a similar range of predators and natural controls as species such as Nezara, populations of specialist pests are rather easier to manage through planting habits: by limiting the continuous area of suitable host plants - i.e. separating small fields of crops by hedges or set-aside, and using mixed-planting and intercropping to their full potential - you can keep most specialist pests from ever reaching numbers where control is necessary or makes any economic sense.
The Other Shield Bugs of family Acanthosomatidae
The Acanthosomatidae are usually treated as rather basal within the Pentatomoidea. Like the Plataspididae, they are offered a move to new and exotic locations by Lis et al, 2017, who indicate that they are rather closely related to the Cydnidae - more closely related, in fact, than some of the other Cydnidae. This is not nearly so well supported by Lis et al's data as the nesting of the Parastrachiidae into a subfamily of the Cydnidae, and the higher-level taxonomy of the superfamily is rather weakly resolved by their study, so - as with the Plataspididae - I am continuing to treat them as separate family.
A single species probably enters Zambia, the widespread Uhlunga typica, which turns up all over sub-saharan Africa, but I've not yet met it. You're probably not going to find them in your crops - any crops, but if you do, they are almost certainly there by accident.
In case you can't guess from the "probably", I have not yet met Uhlunga, and can't show you a picture.
Sorry.
Here's a European one instead.
And - well, it seems like that's all, folks?
*It bothers me that even the "bug" in your machine is not a bug at all, but a moth. I'm never going to forgive you for that, Grace Hopper.
**At one point the linked page notes that compromise proposals to avoid the taxonomic reshuffling that re-assigning a name that has been used for African trees for 6000 years (at least) "unacceptably compromised the rules of nomenclature and created a dangerous precedent" without acknowledging that this is exactly what reassigning the type from an African species to an Australian one does. It is an Australian page, which I suppose explains that...
***Because Wikipedia loves lists and hates talking openly about Africa, I felt obliged to add to this depressing list just three of the many overlooked genocide attempts that Wikipedia neglects to include in its lists (At the time of writing): The 46,000 or so, mostly women and children, who died in the British Concentration camps of the Boer War, and Mugabe's slaughter of 20,000 Ndebele people (specifics can be hard to pin down - dictators are good at keeping records vague). I wavered on including Zimbabwe's first mention - for when Mzilikazi butchered huge numbers of Shona - without including the various other, less-well-known, atrocities committed by the splintering of the Zulu/Ngoni peoples as Shaka sank further into butchery, but decided that it far to central a point of Zimbabwe's 18th century history to overlook. Oh, and yes, I do consider the Afrikaans to be an ethnic group, although they are only about half of those that died in the British concentration camps. I have also not included many of Shaka's atrocities, because I'm on the fence as to whether crimes against one's own ethnic group can constitute a genocide. But they probably should.
****I drew an arbitrary line about 200 years ago, and even within that period, there have been a lot more attempted genocides. Basically if people can create an "us" and a "them", one will use that as a reason to destroy the other.
*****In ideal conditions, little more than 2 months, but in some situations, females seem to have an extended feeding period between the final moult and reproductive maturity.
***Because Wikipedia loves lists and hates talking openly about Africa, I felt obliged to add to this depressing list just three of the many overlooked genocide attempts that Wikipedia neglects to include in its lists (At the time of writing): The 46,000 or so, mostly women and children, who died in the British Concentration camps of the Boer War, and Mugabe's slaughter of 20,000 Ndebele people (specifics can be hard to pin down - dictators are good at keeping records vague). I wavered on including Zimbabwe's first mention - for when Mzilikazi butchered huge numbers of Shona - without including the various other, less-well-known, atrocities committed by the splintering of the Zulu/Ngoni peoples as Shaka sank further into butchery, but decided that it far to central a point of Zimbabwe's 18th century history to overlook. Oh, and yes, I do consider the Afrikaans to be an ethnic group, although they are only about half of those that died in the British concentration camps. I have also not included many of Shaka's atrocities, because I'm on the fence as to whether crimes against one's own ethnic group can constitute a genocide. But they probably should.
****I drew an arbitrary line about 200 years ago, and even within that period, there have been a lot more attempted genocides. Basically if people can create an "us" and a "them", one will use that as a reason to destroy the other.
*****In ideal conditions, little more than 2 months, but in some situations, females seem to have an extended feeding period between the final moult and reproductive maturity.
