Why Locusts Would be Hawks

“War, huh, yeah
What is it good for?
Absolutely nothing.”
Edwin Starr

It’s arguable that things aren’t as clear cut as Starr’s 1969 hit makes out – that in fact, it all depends on perspective. Take locusts for example: if they were able to have a perspective, they’d be inclined to see the positive side of military might and political strife.

Locusts have a tendency to thrive where chaos reigns. War is good for going biblical, and in complex modern conflicts, they could often be considered the only winners. The problem with them taking their spoils of war, from an admittedly anthropocentric point of view, is that they’re spoiling often already-strained lives along the way.

It is a tragic truth that some of the world’s poorest – and most politically unstable – countries fall in the heart of the age-old battle against the family Acrididae’s most notorious member.

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Photo: Christiaan Kooyman/ Wikimedia Commons

Before we get into that, a slight clarification: locusts have very little in the way of hawkish tendencies when they’re on their own – they’re just solitary grasshoppers getting on with their lives. The problem is that they are the ultimate example of individuals which change their character in a group. When coming into close contact, for example in vegetation flushes after a drought, over a few generations, solitary becomes gregarious behaviour – and then comes potential trouble. War offers the chance to increase population density while no-one’s watching on. If caught too late, potentially catastrophic progress could be only at the whim of the wind.

At worst, locust swarms can reach hundreds of square miles in size, and travel vast distances. With each eating its weight in plants a day, the potential consequences are not hard to grasp.

But all is not lost. The fight to curtail locust upsurges brings out a gregarious side to entomologists, too. The field is often seen by outsiders as hermetic – but controlling locust populations is the definition of applied entomology, gone geopolitical and by its very nature, public.

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Photo: ©FAO/Giulio Napolitano. Editorial use only. Copyright FAO.

Annie Monard has been at the forefront of the human-locust struggle for over two decades at the Food and Agriculture Organization of the United Nations (FAO). For her team, tackling the desert locust (Schistocerca gregaria) in particular, is a never-ending and sometimes perilous mission.

“We balance the situation in a country when there are conflicts or instability,” says Monard. “We use information we can get in the neighbouring countries because what always has to be present in mind is that locusts are a trans-boundary pest. Generally, when there are locust issues, it is immediately in three, four countries.”

FAO has three Commmissions to cover S. gregaria’s huge distribution area. One of the three covers West and Northwest Africa – a region which includes Libya and Mali, two countries with current active conflict.

Mali is one of four countries in the region with permanent S. gregaria breeding populations. With access to the northern part of the country currently impossible, monitoring relies entirely on reports from locals and retired staff living in that area. These can be delayed or incomplete, but it’s something. At the same time, surveys have been intensified in bordering areas of neighbouring countries.

Instability can breed a pragmatic sort of creativity, and it is in evidence here. Soldiers in the national military have been given basic training to report on locust sightings, giving some added, combat-style ‘boots on the ground’ to the intelligence-gathering effort.

But there is conflict and there is conflict – and Yemen currently represents the gravest end of the spectrum. “Forget everything,” says Monard. “The same message is coming back: no surveys were carried out due to insecurity. So I mean, there is nothing. It is not possible to do the basic work in that country.”

When upheaval comes, agricultural budgets are often the first raided – as was the case during Madagascar’s military coup in 2009. Monitoring stopped, locusts bred unwatched, and populations surged quickly.

In frontline countries – those with permanent locust habitats and breeding areas – the aim is to survey as thoroughly as possible, aided by technology such as satellite imaging, drones and the FAO’s elocust system, which allows national field staff to input standardised data. If locusts would have a preference for states of war, the human counterinsurgency effort is becoming increasingly sophisticated.

Timing is everything in this war-within-wars. There’s no use trying to wipe out every locust, so you have to know when there’s enough massing to justify a strike. “We advocate a locust preventive control strategy relying on monitoring, early warning and early reaction,” added Monard. “Our aim is to try and be as proactive as possible – not acting as ‘firemen’.”

Though this human Vs. insect struggle offers no prospect of a definitive winner, and containment the only realistic prospect, rarely has entomology been so vital.

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Insects: today’s fashion icons

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Creobroter gemmatus doing a little turn on the catwalk. Photo: Wikimedia Commons

Insects are no slaves to fashion – they’ll evolve their looks according to what’s needed for survival, whether that means growing enormous horns on their head, losing their wings, or turning the colour of a pollution-stained surface.

But that doesn’t stop the creators of taste and style having a go at shoehorning insects into the fashion world. Members of the orders Lepidoptera and Coleoptera have been consistent influences on the work of the fashion house of Alexander McQueen, for example, while Gucci and Dolce & Gabbana have gone big on bees.

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McQueen’s bag-based take on insects. Photo: Bagaholicboy.com

It could be argued that this marks a considerable shift into the mainstream. Insects have always had their fans among subcultures, and if you attend an entomological fair, you’re very likely to be doing so along goths and metal fans as well as purist insect enthusiasts. Yet this latter-day aesthetic admiration seems different. Never have insects been so on-trend; not underground but out and proud.

It’s quite possible to argue, though, that the visual power of insects has been tapped almost as long as there’s been civilisation, from the Scarabs of the Ancient Egyptians to the totemic insects of aboriginal peoples. There’s no doubt that insects look cool, and have been making an impression for time immemorial. Every single student on the Entomology MSc this blog aims to represent would strongly agree with this position.

The problem is, it’s not clear whether looking cool is proving any use to them in this age of maximal human destruction. At the same time as all this high praise of the aesthetics of arthropods, the other notable high profile insect-related theme is their decline – so much so that the issue recently made the front page of the New York Times Magazine. Our very own Prof. Leather has also commented on the phenomenon of ‘insect apocalypse’ extensively, calling for long-term data sets to counter the shifting baselines of successive generations which mean a full understanding of changes in insect populations is never grasped.

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Photo: Gucci.com

How can the doyen of designers also be the enormous arthropod in the room when it comes to the global threat to species’ survival? It appears we’re culturally confused about insects in the culture known as ‘The West’ – we’ll happily co-opt their image, but see a living insect in your home or near your picnic and it’s likely to be a case of smack, goodnight. Add to that the deranged media panics about disease-laden ladybirds and mosquitoes, or even the ultra risk-averse responses to the notorious non-insect, the false widow spider, and it seems clear that there’s a huge gap in perception between threat and fashion that needs to be filled, urgently.

On the subject of spiders, Camilla Brown, an arts writer friend of mine, went deep into our confused attitudes around arachnids, with a specific focus on gender, for her MA final work ‘Spider Woman’ (NSFW content warning). It looks at notable spider-themed works of art and embedded childhood fears, certainly touching on themes that are also relevant to the discussion of insects in culture and society more broadly.

So, what are insects to us? The miniature bogeymen stalking our waking dreams, convenient ornaments, or not worth thinking about at all? Perhaps worse than a panic about insects and the rest of the arthropods is an indifference to their ecological relevance.

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Oak treehopper, Platycotis vittata –another big player in the style stakesPhoto: Wikimedia Commons

Finding a solid middle ground between fetish and fear needs to start with a greater understanding of the myriad roles that insects play. They are far from just pollinators (even though that’s hardly much of a ‘just’); they’re also pest controllers and decomposers of the highest order, and an enormous supply of meals to animals higher in the food chain. Without them, careful balances may become irreparably skewed.

It seems apt to brush off the shallow wants and desires of the human in the era where their consumption seems to be akin to a declaration of war on the other residents of planet Earth. Yet nature and our culture are not mutually exclusive entities: they’ve been deeply entwined since we were out in the wild and we started to try and make sense of our surroundings in a more profound way than addressing basic needs. Fashion designers riffing off insect wing venation is simply an extension of this.

So outright-dismiss insects making an impact in the Instagram age at your peril. More visual presence for insects can hardly be considered a bad thing – and there’s maximum scope to do much more than haute couture. Interestingly, on this theme, it was recently mooted that insect-related street art could be a way of bridging the gap between the visual and the actual by providing a constant reminder of the vitality of nature in people’s everyday lives.

Perhaps in the coming years we’ll see more attempts to bring science and culture together in a very necessary joining of dots – moves like the University of Nebraska-Lincoln offering an Insects in popular Culture module as part of its entomology qualification. Science is in no way discredited by the suggestion that the zeitgeist may have to be ridden from time if we’re to become more even-handed participants in a world shared.

On Insect cocks

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Cock. Penis. Dick. Wang. Whatever you call the male appendage, this is an area of insect physiology where things get pretty wild. Or perhaps more accurately, wilder than the usual.

But let’s start scientifically-correct: in the insect world the closest thing to the human penis is more properly known as the aedeagus. But ‘closest thing’ does not in any way imply great similarity. It’s actually part of the insect abdomen, and the external part of the male’s sexual weaponry is a phallus of extremely various flaps, hairs and hooks. Still with this? Good.

When it comes to shape, describing the situation as complex doesn’t get anywhere near to doing it justice. Menno Schilthuizen’s account of genital evolution is a comprehensive overview (far more so than can be included here), highlighting a wonderfully alien world of ‘prongs’, ‘pegs’, ‘springs’ and ‘titillators’. If insects are purely in it for the passing of genes, they could’ve fooled us.

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Amazing aphid dicks: from Wieczorek et al, 2011 

There’s so much to say about the morphology of aphid appendages alone that the main journal paper on the matter comes in two parts. For relatively small insects, aphids come with a significant package – “relatively large and discernible under a hand lens or even with the naked eye”. The paper includes such descriptive gems as “a few circular pits distributed mostly in its medial part. Sclerotized arms with distal part rather long and thin, and proximal part shorter and wider. Aedeagus long, inverted question mark-shaped.” And that’s just the aphid Drepanosiphumplatanoidis. Big name, big aedeagus.

Smutty jokes aside (but not for long), in insect taxonomy, male sexual organs can be extremely helpful in establishing exactly what species you’re dealing with. In fact, it can often be the only way of making a certain identification. So far, so useful, to us as well as them. But how do insects actually, you know, do it? Again, this is no simple matter.

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Normal for dragonflies: from Miller, 1991

The ‘lock and key hypothesis’ is an idea that has persisted in entomology – and, naturally,
argued over. It asserts that male and female sexual organs of an insect species, whatever wacky shape and size they are, have evolved to only be the exact ‘fit’ for each other. The theory, however, has been largely discredited over the years.

What’s abundantly clear is that sex is rarely anything straightforward in the insect world – there’s little by way of proxy for missionary. Dragonflies are a good go-to example for the messiness of it all – so much so that their sexual antics inspired a New York Times article, in which the slaty skimmer (Libellula incesta) is described as having a “fairly rococo penis”. Sex begins with what constitutes foreplay – the male grabbing the female at the back of the head – while dragonfly dongs are not just about depositing sperm, they’re also about removing that of rivals. Naturally, females are tooled up to stop that happening, if at all possible.

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Brutal bruchid beetle bell-end: Wikimedia Commons

The mealworm beetle (Tenebrio molitor) also has a dick geared up to dispatch the genes of its rivals. In the words of this paper on the matter, it “comprises a central shaft enclosed within a flexible sheath covered with chitinous spines. As the shaft extends within the female’s copulatory bursa the sheath and its covering of spines rolls back producing a `scouring’ effect.” Lovely.

With schlongs often more resembling torture implements, things can get even more brutal. Males of the bruchid beetle (Callosobruchus maculatus) actually damage the female’s reproductive tract during sex, and females, understandably, kick them for it. If she doesn’t kick, injuries tend to be worse after a longer sex session. Yet according to this paper, the carnage is not a deliberate act of destruction by the males, just an unfortunate by-product of them evolving weapons that are literally weapons. Why, it’s not yet known, but the theory is its all about being able to cling tightly to their ‘loved’ one.

If this blog puts insects in danger of being adopted by the alt-right as beacons of ultra- masculinity, hold that thought right there. Transgression of gender norms is happening in Brazilian caves, don’t you know. In the louse genus Neotrogla, it’s the females with the penis-like protrusion, and the guys with a chamber comparable to a vagina. A very niche re-definition of ‘wearing the trousers’ for sure, and in marked contrast to the species of beetles and dragonflies using their phallus to screw over their rivals with a bit of sperm scooping, our ‘macho’ cave-based females are using theirs to collect it up. Through all the kink and horror, life finds a way.

So there, a piece about insect nobs has been published on the Entomology MSc blog. I can only hope this comes up in the exams in March, making things a little less hard. Too much smut? Probably.

 

Britain’s Next Top Pest

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Our Entomology MSc gang have just had two weeks hearing from some of the key players in the biological control industry. While there were many invasive insect pests mentioned that are currently giving UK growers cold sweats in the middle of the night, a few names kept cropping up.

Without further ado, here’s a run-down of just a few of the headline crop-hungry taxa posing new threats on these shores.

Spotted wing drosophila (Drosophila suzukii)

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Not the most appetizing plum, thanks to D. suzukii (photo: Martin Hauser/ Wikimedia Commons)

Despite its catchy name, nobody hopes to catch this fruit fly on their crop. Originally from South East Asia, it’s been rapidly expanding its range in Europe, and was first seen in the UK in August 2012. Unlike like other Drosophila, which tend to go in for decaying and rotten fruit, D. suzukii uses its serrated ovipositor to lay its eggs through the skins of otherwise undamaged fruit. A neat evolutionary advantage for it, really bad news for growers of soft fruit.

The pest control industry is very much all over trying to get the better of this species, though there is no perfect formula. Research has suggested that using biological methods, in this case entomopathic nematodes and fungi, can reduce population development, but can’t stop outbreaks.

South American tomato moth (Tuta absoluta)

Another great name, another insect to strike fear into growers. Unsurprisingly, it’s massively into tomatoes, and can do enormous damage to crops when left unchecked – to the point when they can finish off the lot. Although numbers of outbreaks in the UK are still relatively small, the potential to penetrate all parts of the tomato plant means that any arrivals, such as in imports of Spanish tomatoes, must be taken very seriously indeed.

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The tomato isn’t looking great either (Photo: TNAU Agritech Portal)

Full development from egg to adult has been seen in a wide range of temperatures, and a 2013 study concluded that Tuta is “well able to develop under temperatures that would commonly be experienced in UK glasshouses”.

Other research has highlighted the potential of natural enemies to counter this tomato-loving moth, with Macrolophus and Nesidiocoris tenuis, two Hemipteran egg predators, now seen as having the best potential to make inroads into populations. The problem with this approach is that sometimes a beneficial insect can become a pest, and in this case, the biocontrols have been known to do plant damage themselves. Nothing is ever completely straightforward in the world of pest management, it seems.

Diamondback moth (Plutella xylostella)

There have been recent spikes in numbers of this lover of cabbage and cauliflowers, sparking natural concern among growers. Evidence is mounting that it’s surviving winter here, as well as resistant to pesticides.1280px-Plutella_xylostella1

The fight is by no means over, however. Intercropping – growing a different crop in proximity to the main one – looks like a promising tactic in taking on the pest. A 2010 study showed that planting onion, tomato or pepper with cabbage was as effective as spraying.

Melon thrips (Thrips palmi)

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Photo: Forestry Images/ Wikimedia Commons

Although this thrips species can’t survive the British winter, it can establish with protected crops, and is extremely unfussy in its choice of meal. As such, it’s as much a threat to growers of ornamental plants as it is to those in the fruit and veg business.

What’s more, it’s another insect known for being highly pesticide resistant, so effective biological controls are certainly what’s called for here. It seems likely that a mix of entomopathic nematodes and fungi may well be the dream team for tackling both the larval and adult stages.

 

Is that it?

Far, far from it. The insects featured here are certainly not the only ones that could potentially do significant harm in UK agriculture, should they both get the chance to arrive and find a way to consolidate their numbers here.

DEFRA’s top six of the very latest potentially damaging pests and diseases features a pair of longhorn beetles from the east, while the UK Plant Health Risk Register is a fascinating and somewhat frightening source of information about potential threats to the flora of this island. Currently listing 1,024 pests (not just insects, however), it serves to highlight that amidst the great advantages to global trade come some pretty serious pitfalls.

The prizes for pests that manage to establish themselves in the UK’s famously un-tropical climes are significant – and in an agricultural environment of reducing pesticide effectiveness and use, controlling their proliferation is a multi-faceted and often complex game.

Successful pest management has to take into account factors like the temperatures insects operate in, where they operate in the crop canopy, the need to tackle both adult and juvenile stages, and compatibility of biological control methods with insecticides and fungicides. It also needs to factor in a comprehensive clean-up after the pest has been beaten, to prevent an immediate repeat of the nightmare all over again.

While there are plenty of checks in place to try and prevent invasive pests getting the chance to test their resolve against the UK climate, it’s practically impossible to prevent every insect of potential harm making it past the border. The prerogative is that when they do show up, they are reported quickly, and expert advice sought when needed. If the last fortnight’s lecturers were anything to go by, there certainly is the expertise out there to nip most comers in the bud before scares become crises.

Spiders and insects: Evolution’s Tom and Jerry chase?

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Among the many interesting points raised during our recent Diversity and Evolution of Insects module was the idea that spiders and insects may have been involved in a sort of cat and mouse pursuit through the fossil record.

It’s certainly the conclusion David Penney reached in his 2004 paper looking at insect and spider family diversity over geological time. It’s suggested here that the rate of exponential increase in diversity was the same for both groups, and that one’s line of rapid diversification – known as radiation – followed the other.

Both insects and spiders tend to be linked with the history of flowering plants, but interestingly, the study also suggests that the major radiations of both these classic antagonists were out of the way a good 100million years before the flora joined the party. This being the case, the arms race began without the need for the habitats that we’d probably associate with the modern tussle of flying insects and web-weavers.

Co-evolution has been proven to be more likely when there’s a direct interaction between groups, and at least one dependency, so the idea of a hunger so profound it transcended the ages certainly sounds plausible. Yet it’s not a view universally shared.

It’s hard to conceive of the struggle between insects and spiders without thinking of webs – and the diversity of arachnid species is linked with the diversity of web design. But in the poetically-titled Tangled in a sparse spider web, researchers at the University of Barcelona muddy the waters of the ‘insects lead, spiders follow’ story of speciation.

They make a case that the diversification of spiders and their web-building approaches was all about moving to different habitats and making use of food resources in an increasingly structurally complex world. To be clear, it’s abundance of prey, they say, that was more significant in driving a species-defining approach to webs rather than its diversity. Loads of flying insects, yes, but not necessarily loads of different ones. They also make the case that the explosion of orb-webs couldn’t have happened at the same time as the insects were on their fiercest period of diversification.

Searching for trends through what remains of the species that have been here and gone is a notoriously tricky business – something that is more than acknowledged by the authors of the different theories offered here. Missing data is one of the foremost problems with scouring the past for clues that may illustrate a trend, while the ‘family trees’ considered in invertebrate evolutionary studies are often complicated and controversial; subject to different interpretations and revisions.

So, has predator chased prey through the ages, or are things a little more complex than that? Well, this is science – never the easiest place to get a neat narrative from. So while you can find shadows of Tom and Jerry, Road Runner and Wile E. Coyote, Bugs and Elmer and the rest if you trace the lineages of Arachnida and Insecta, pinning evolutionary trends on a hunter-hunted analogy alone probably won’t quite cut it.

Apocalypse by mosquito?

As part of our molecular tools lecture, expertly executed by Joe Roberts, we discussed the recent advancements of gene editing and its use in the eradication of malaria in Africa. Crispr is the cutting-edge gene editing tool that has garnered a lot of attention since it’s discovery in 2007. Further developments have led to it being the simplest method for editing the nucleotides on a DNA strand altering the original gene which can result in resistance to diseases, alleviate genetic disorders or treat blood diseases.

Despite its multitude of uses genetic engineering has been faced with large amounts of controversy. Gene drive, which is the promotion of specific genes in a population that cause infertility or death through release of carriers into the wild, has faced mass criticism due to the uncontrollable nature of the concept. Once these genetically engineered individuals are released, there is little that can be done to prevent the spread of the unwanted gene across species through natural hybridisation. There are also concerns over the potential impacts of eradicating an entire species from an ecosystem, which could result in a collapse if the eradicated species is an important food source-as in the case of mosquitos.

Malaria-carrying mosquitoes of the Anopheles family are one of the prime candidates for gene drive control. The infected females spread malaria through their bites, which release the parasite into the bloodstream of the unlucky animal. Malaria is life threatening, killing half a million people annually so control of the vectors (mosquitoes) is of particular importance. Many studies have been done into the prospect of gene drive control of these insects, with the most recent being the release of genetically engineered males into Burkina Faso that you may have seen on the news in the last couple of weeks, treated as the new apocalypse.

The release of these mosquitoes is being controlled by the non-profit research organisation “target Malaria” as a test for the potential release of gene drive organisms. The mosquitoes being released in their experiment are all sterile, thus are unable to pass on their edited genes. They are simply being released to gather data on their dispersal and won’t last more than a few weeks in the ecosystem. So, no, we haven’t reached the point of using gene drive in the control of malaria quite yet, but the organisation is hoping to eventually use their mosquitoes to eradicate Anopheles in sub Saharan Africa, albeit with more work needing to be done.

Whilst gene drive systems have been highly effective in population control for lab studies, the issues around potential hybridisation needs to be considered and it’s been discovered that these mosquitoes are capable of developing resistance to the edited genes through random mutations. Lab work is limited and simply can’t match the population size found in the wild-thus the rate of mutation faced by their gene drive experiments is much lower as they have fewer individuals to experience a random mutation. Therefore, actual field results may be hampered by development of resistance.

We are faced, then, with the final dilemma. Does the risk befit the reward? Do we risk the transfer of these genes through hybridisation to save the lives of half a million people a year? Is the rate of mutation high enough to negate the entire gene drive system in the wild populations? All that can be done is further research, taking the necessary precautions before leaping into a potentially disastrous situation. Which is exactly what the Burkina Faso release is for.

Parental Care in Insects

The concept of parents looking after their babies is easily recognisable. We were all cared for when we were younger (even if not by our biological parents); fed, clothed and housed. We recognise the same urge when we see a cat cleaning her kittens or a bird collecting nest materials, but do we see it in insects? Well, more than you might think.

Only about 1% of insect species show parental care; selection pressure favours lots of offspring, effectively limiting parental care to species which produce fewer young. Parental care can mediate the transition from solitary to group or family living, both for an individual and on an evolutionary scale. It is likely to have developed as an altruistic trait to enable parents to better ‘pass on their genes’ by improving the survival of their offspring, even at the cost of their own energy, food, or even future reproductive opportunities. It may be evolved in environments with high selective pressures such as predation risk or reduced food availability.

Some insects show pretty much every level of sociality that you can think of, so here’s a walk-through of what insect parental care looks like. Through egg care, larval care by one of both parents., and the formation of family groups, this is the insect guide to good parenting:

Egg care

In some species, parental care starts before the young even leave the egg. Female earwigs groom their eggs to remove harmful mould spores and secrete symbiotic bacteria onto the larvae which are both antibiotic and anti-fungal. One study found that only 4% of European Earwig (Forficula auricularia) eggs hatched when they were left untended, as opposed to 77% for tended eggs. Mothers do the bulk of the offspring care but for some species the father takes the burden.

Male water bugs (Belostomatidae) brood the fertilised eggs on its back until they hatch. Carrying the eggs around makes the males more vulnerable to predation and hinders their foraging, making a large energetic expense to rear their offspring. It also stops the male from being able to mate again until the eggs have hatched.

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Male Giant Water Bug carrying his brood (Matt Tillett)

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Female European earwig, (Foricula auricularia) with egg brood and nymphs (University of Florida)

 

Uniparental care

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The Australian Hornet (Abispa ephippium) with her nest (Ian Sutton)

Potter wasp (Eumeninae) females build small clay nests for their larvae, bringing them food, defending them against predators, repairing damage and cleaning debris from the nest. Males play no role in the larval care but do patrol nest sites to find females to mate with.

 

 

Biparental larval care

Burying beetles (Nicrophorus spp.) take it up a level with both parents caring for their brood. Not only do they stock their larvae’s underground nest (or ‘crypt’) with a decomposing carcass (yum), but they also feed them regurgitated meat if begged. If there isn’t enough carrion to go around, parents will cull the most demanding larvae; whilst this might seem harsh, it ensures the survival of their less needy siblings. Although the parents don’t form the monogamous pairs often seen among vertebrates, they will stay together until their larvae reach adulthood.

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Nircrophorus vespilloides individual feeding its young (Dr Clare Andrews)

Family groups

Cockroaches might not initially seem the most likely parents given their occasionally cannibalistic tendencies but show some of the most comprehensive parental care of the insects. The females of some species are viviparous, gestating their offspring under their wings and producing a protein and carbohydrate rich ‘milk’ to feed their young nymphs until they are old enough to be ‘born’.

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A pacific beetle cockroach (Diploptera punctata) ‘giving birth’ to nymphs. This species also produces cockroach ‘milk’ (Emily Jennings)

Both cockroaches and burying beetles, unusually for insects, form family groups. In cockroaches this is because nymphs need to receive the gut protozoa essential for digesting cellulose from their woody diets. They lose the protozoa after every moult meaning that to ensure the nymph’s survival the adults have to stay with their offspring until they reach adulthood.

It is thought that this feeding was the key which allowed ancestors of modern termites to become eusocial. Termites are very closely related to cockroaches and these family groups expanded and evolved to become eusocial colony organisms. Living close together with millions of their ‘siblings’ allows termites to be sure of security and a food supply and allows traits like monogamy, foraging and nest inheritance to be developed. The switch from parental to sibling care is thought to have led to social behaviour forming in ants, wasps, and bees.

Evolution of sociality

But what is the glue holding these parents to their offspring? It’s surely not the big eyes, fluffiness, and helplessness that draws us to babies, kittens, and ducklings- even entomology students would struggle to call a cockroach nymph cute. It seems insect ‘families’ are reliant on pheromones as a recognition mechanism. Earwig nymphs’ pheromones reflect the quality of the food they’re being given to influence their mother to provide more food if needed. Cockroach nymphs use similar pheromones to aggregate with their parents and siblings and are able to distinguish non-siblings.

Brood care is thought to also have driven formation of families and social groups in vertebrates. The evolution of parental care in insects can be a model for the evolution of parental care in birds, fish, and of course mammals. It seems that you might have a lot to thank cockroach milk for your survival to adulthood.