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.

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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.

 

In defence of common names

In our Dipteran discussions on Tuesday last week, the idea of doing away with all insect common names was mooted. While this may have had some support from MSc colleagues in the room, I think the majority were probably with me in internally screaming “NOOOOOOOO!”.

Let’s be frank from the start: yes, our good old Anglicised common names are mostly easier to remember than scientific names, unless you’re a fluent Greek or Latin speaker. But that’s not why I’m here to stick up for the commoner.

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It’s well worth first acknowledging that there are problems with common names. Many are seemingly endless variations on a pretty loose theme (see the myriad ground beetles or hoverflies), and they can be different at national and even local level, de-standardising what is an internationally-agreed nomenclature and even muddying the waters of the body of research on given species.

But it’s not like the waters aren’t muddy enough in the first place. It’s arguable that things haven’t changed that much since 1942, when the Journal of Economic Entomology published an editorial stating:

With the scientific names of insects in perpetual chaos, due to the application of the law of priority, the splitting of species and generic concepts, and the endless shuffling of species from one genus to another, common names have come to have much more significance and importance than formerly.”

Common names have a tendency to cut through the noisy clanging of taxonomic debates – but they can do more than that: evoke, romanticise, or simply tell it like it is. On the latter, common names can tell you what an insect feeds on (pollen beetle, currant aphid, fungus gnat, dog tick), give you a crystal clear idea what an insect looks like (scorpionfly, giraffe weevil, orchid mantis, violin beetle), and let you know where it likes to hang out (larder beetle, house fly, museum beetle, bedbug).

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Devil’s coach horse beetle – Ocypus olens (Wikimedia Commons)

They can also simply bring a bit of fun to what can seem to outsiders like a dry discipline. Science is not forever vanquished by the simple admission that talk of fairyflies, ugly nest caterpillar moths, assassin bugs, beautiful demoiselle darters and bombardier beetles makes the world a slightly lighter, more wonder-filled place.

Common names can even reveal a bit about our culture. Why on earth shouldn’t Britain, a country steeped in existential angst and the occult, have brought its language to bear on the death’s head hawk moth, devil’s coach horse and deathwatch beetles?

As if to prove the joy of an apt common name, when Tuesday turned to Wednesday and we were introduced to the Lepidoptera via a photo of the Picasso moth, there was a notable instant improvement in the mood of the room, previously somewhat tense ahead of the afternoon’s assessed practical.

The power to evoke should not be underestimated in the communication of science. From a personal perspective, a life-long love of beetles would have been far less likely sparked by Lucanus cervus than stag beetle. The public are not a bunch to be sneered at for their failure to appreciate scientific correctness – and what’s more, need to be brought along as the pivotal role of insects in supporting human life becomes ever clearer.

Picasso moth M Greeshma

Picasso moth – Baorissa hieroglyphica (photo: M. Greeshma)

I agree wholeheartedly with Michael J. Samways, who in his 2005 book Insect Diversity Conservation urged experts not to shy away from charismatic ‘icon’ species and to use their common names, “so as to give the conservation mission warmth and familiarity”.

In case I haven’t made myself quite clear, I’m not just trying to make life more difficult for Giannis, Cyprus’s representative on the course, who’s been sitting through the Hellenic-monikered species being reeled off as part of our Biology and Taxonomy of Insects module with a distinct air of ‘heard it all before’.

And all of this is absolutely no argument against scientific names per se. Of course, they will always have primacy – but they shouldn’t sit on their own, or they might just find themselves in sparse company.

Behind the Moth Meme

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Unless you’ve digitally cleansed your life recently, you’ll probably be aware that moth memes have taken over the internet – so much so that there is now, inevitably, a Reddit page dedicated to this unique sub-group of social media fodder.

The focus of this frenzy of meme-making has been moths’ famed love of artificial light. But here at Mastering Entomology, we’ve decided to delve a little deeper.

First and foremost, though, it’s worth pointing out that there are plenty of moths that fly during the day – so aren’t the types to be suckered into the seductive glow of a lamp. A study by Florida Museum of Natural History suggested that 15-25% of all Lepidoptera are day-flyers, while Butterfly Conservation has helpfully produced an overview of the UK’s non-nocturnal moths.

But of the nocturnal species, is there really a deep craving driving moth orientation towards our light sources? The fun-killing simple answer is probably no. The expert consensus seems to be that it’s all a misunderstanding; that they’re actually looking to orient themselves by the moon, and they’re simply drawn to alternatives because they’re brighter. As they move closer, their ability to triangulate is thrown off kilter, resulting in them returning to the light repeatedly.

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But given the distraction, as opposed to attraction, our light sources bring, are all moths equally likely to zone in on the bright lights, and are all electric lighting types equally likely to bring lepidopterans into their glow? That’s another no and no.

The tendency to head for the light could be greater for moths from areas with little light pollution. Altermatt and Ebert (2016) found that in the case of the small ermine moth (Yponomeuta cagnagella), ‘city moths’ from populations that had experienced high amounts of artificial light were less likely to fly to light under lab conditions than those from ‘dark sky’ populations. It has been suggested by several studies that natural selection should favour those less drawn to artificial light – pretty logical stuff – and this research provides some evidence that such selection may indeed be happening.

Altermatt and Ebert have serious form when it comes to advancing knowledge on moths and light. In their 2009 study with Adrian Baumeyer, male Yponomeuta cagnagella and Ligdia adustata were seen to be 1.6 times more likely to make a beeline for an artificial light source than females. A good argument to settle the ‘smarter sex’ debate, perhaps.

A PhD study in Exeter has recently shed further light (pardon the pun) on the type of illumination most attractive to larger moths, finding that short wave lighting attracts both greater numbers of species and individuals than long wave.

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The interplay of moths and light is, alas, not all online laughs and levity. There is growing evidence that artificial light may be having deeper effects on moth numbers than simply the deletion of those flying at speed towards the lamp. While the fact they are drawn to light is firmly established, there is evidence that it could be reducing moths’ attraction to each other.

A 2015 study in the Netherlands by van Geffen et al looked at the mating habits of Operophtera brumata, a member of the Geometridae family, when tree trunks were lit with different-coloured LED lighting. What the first phase of the research discovered was two-fold, and fascinating: a significant reduction in females on the illuminated trunks, again suggesting a sex bias in light attraction, and an inhibition of mating when they were under the lights. A side note, though: perhaps appropriately for this sexy moth discussion, more females caught on trunks lit with red light had mated than those with green or white light.

Mating is not the only matter that will pique concern amongst conservationists. Other research has found links between feeding and artificial light (they appeared to do less when subjected to it) and caterpillar development (they reached lower mass under white light and pupated earlier under green and white).

There is clearly multi-faceted interplay between moths and light, and a sense that we’re only beginning to understand the mechanics and effects of it. The ability of species to coexist with increasingly dense human habitation is a hot topic, so knowledge in this area is only set to grow in the coming years. Far from every aspect of this issue has been covered in this blog, but in the interests of brevity, it might be best to wrap up (although most of those readers who came for the memes have probably gone already).

Final note: this week and next we’re doing the taught elements of Biology and Taxonomy of Insects, the second module of the Entomology Masters here at Harper. Next Wednesday we’ll be looking at Lepidoptera, increasing our knowledge of these complex yet internet content-friendly insects.

Meet the new ento-blogging team

New year, new team of aspirant entomologists writing for Mastering Entomology – and this time around there’s four of us. With no further ado, let’s introduce the team…

Ant lion

Here’s an antlion Sam found earlier

The antlion fanatic

Hey, I’m Sam. I’m actually a fairly recent convert to the ento crowd. My undergrad was in zoology, where I was considering going into conservation or behavioural research. As the leader of the course was an entomologist I did learn a lot about insects, but my passion wasn’t really ignited until a trip to Africa in my final year. In a place where monkeys and hippos are the norm, I found greater fascination in the intricate pitfall traps formed by the antlions that surrounded our hostel. That trip cemented in me a desire to understand the behaviour of insects and its evolution. Which is exactly why I’m here at Harper Adams. I’ll try my best to share all the interesting behaviours that I come across in my studies.

The future curator

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…and a death’s head hawkmoth Dom photographed earlier

Hi, I’m Dominic. I chose to study Entomology as I am very passionate about the subject and want to improve my knowledge and understanding of Insects. Ultimately, I wish to work as an Entomological curator where I can look after the important collections held within museums, educate the public on insects and hopefully conduct my own research to help the conservation of entomofauna and the habitats they reside in. My main interests in Entomology are Lepidoptera and Coleoptera (predominantly Moths and Scarabaeidae). I am fascinated with the way that Insects interact with and influence other organisms as well as looking at their roles in various ecosystems, I am also intrigued with how Insects have impacted human culture. In this blog I hope to write about insect behaviour, interactions, historical importance, environmental impacts and any other Entomology facts I find interesting.

 

Entomologists on wrekin

Gary (L) on a collecting mission with fellow members of the Harper ento crowd

The outlier

I’m Gary. You could certainly argue that I’m not the typical Entomology MSc student, having spent the last decade-plus in writing, communications and journalism. The love of insects has always been there, mind – just, it’s fair to say, lying somewhat dormant for a spell. Heavily influencing my taking of this somewhat tangential turn was time spent in the Prespa National Park in Greece, Albania and the Republic of Macedonia, where, similarly to Sam, I spent much of my time staring in awe at the biodiversity on the floor rather than looking out for bears, wolves or the magnificent array of bird species. Though I’m not exactly relishing the statistics that are to come as we work towards our final research projects, an insect-collecting trip up the Wrekin last week with some of my fellow Ento postgrads firmly fixed in my mind that I’ve made the right, albeit slightly curious, decision. Twitter: @garyfromleeds

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Niah’s pet aphid mama

The pest patroller

Hi, I’m Niah, the token Integrated Pest Management student on this blog. I come from a science background, having just completed my Bachelor’s in Biological Science, but I knew next to nothing about entomology until my interest was sparked on a placement at the Warwick Crop Centre. Having spent a summer emptying traps, carrying out pesticide trials, and compiling citizen science moth counts into a report, I decided that pest management was the way forward! As well as singing the praises of biological control, I am especially interested in social insects, months, vectors of human disease and, of course, aphids. It’s quite a mixed bag but I’m looking forward to including some of them in this blog!

We’re aspiring to bring you some blog content that’s as diverse and intriguing as the world of our favourite arthropods. If we can get even remotely near, we’ll have done a pretty good job.