A good year for mind-controlling ladybird-munchers

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Dinocampus coccinellae: a fearsome foe of ladybirds. Photo: Wikimedia Commons

For my Masters Research Project (MRP) I am taking a look at righting and death-feigning among beetles, including a couple of ladybird species. I made the decision that I would try and work with natural populations wherever possible – the only problem with that, of course, is that nature can be the cruellest cohabiter.

Upon setting up a colony of seven-spot ladybird (Coccinella septempunctata), it quickly became apparent that I had a bit of an issue; namely finding quite a few specimens protectively guarding yellow cocoons. Doing such a good job of it, in fact, that it was almost impossible to remove them from both cocoon and plant. Dinocampus coccinellae had joined my project uninvited.

I was aware of possible parasitism of beetle juvenile stages, including those of ladybirds, but not the wasps with a penchant for taking on adults. Little did I know that this is the Braconid wasp D. Coccinellae’s stock-in-trade – and one that it’s building up such a reputation for its it’s started to become a minor mainstream news story. Indeed, once I was aware of it, I started to see ladybirds in their natural habitat sitting on cocoons seemingly everywhere, like some strangely beautiful horror movie in the undergrowth.

Coccinella septempunctata in aggressive cocoon-cuddling mode. Photo: Brad Foster (Twitter @bradwaspfoster)

The parasitoid was first given a full biological description in 1926 after it was first noted in Europe, and since then, boy has it settled in.

One facet of the appeal of insects is a feeling that the aliens are among us already – and indeed parasitoids really did inspire that scene in the film Alien. With D. coccinellae, it is isn’t just about depositing an egg inside the ladybird and leaving its young to, all being well (from the wasp’s perspective of course), burst out of its host’s body an adult. It goes in for full-on control and manipulation, creating ‘zombies’ from ladybird hosts that guard a wasp cocoon spun between its legs by larvae after they’ve had their feeding fun. In its sensory-controlled state, the ladybird twitches to deter predators as the larvae pupates and hangs in there for adulthood. They do a fine ‘bodyguard’ job too, with studies showing only 15% survival against predators with host protection, and 65% with.

This may well be a problem of particular concern to the seven-spot ladybird, as research has shown that while it’s wily wasp enemy can decimate its populations, successful parasitism and emergence rates of the wasp are significantly lower when it makes an ovipositional attack on the invasive Harlequin ladybird, Harmonia axyridis, while the two-spot ladybird, Adalia bipunctata, is an unsuitable host altogether. To make matters much worse for C. septempunctata, it has been demonstrated that its toxic defence chemicals actually act as a considerable attractant to D. coccinellae. Bloody hell, nature.

It seems that a perfect storm is gathering, where a wasp, a highly-successful invasive competitor, a fairly narrow (and early in the year) breeding period and other environmental stressors are combining to make life extremely difficult for one of the UK’s classic ladybird species. Will it withstand the onslaught? Too early to tell – but there are certainly reasons for concern.

As for my experiment, maintenance of colony health since the first sightings has proved a game of watching intently for signs of parasitism, removing rapidly, rinsing and repeating. But stare into D. coccinellae’s intensely beautiful shiny green eyes under a microscope and you can’t help feeling this is an animal you’re never going to quite have the measure of. Allow me this excessive sweep of anthropomorphism: its gaze really does follow you around.

While my run-in with this small wasp has provided much by way of irritation, once you’ve taken a step back from your emotional response, it’s hard not to simply admire a highly-specialised species succeeding in its niche. That is, however, likely to be extremely cold comfort for those looking to conserve the UK’s native ladybirds.

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An Update (Part 2)

Welcome back peeps! Here’s the second part of the overview/highlights of what we’ve been getting up to so far on the course:

Module 2: Diversity & Evolution of Insects

This module was a nice transition from the previous module content-wise. The first day was a mixed bag, it started with a lecture from Prof. Simon Leather (@EntoProf) on the history of entomology as a subject and insect paleontology (come on, who doesn’t love a bit of Meganeura spp.). Followed by Dr. Andy Cherrill giving a lecture on intraspecific variation. Theeeeen, back to Simon, with a lecture on the super weird, awe-inducing and ever so slightly ridiculous aphid life cycle. The day concluded with the first guest speaker for this module: Professor Tony Dixon! He gave us a lecture on aphid thermobiology and coccinellids (ladybirds, namely on generation time and their usage in biocontrol). He was Simon’s PhD supervisor! It was a privilege to be lectured by someone who has been in the game for so long, is still publishing research and has taught one of our lecturers. The next day was also a healthy mix of topics, covering soil biodiversity to aquatic insects and estimating insect species diversity.

Leading on from the previous day, we had a lecture on Acari (ticks and mites). The study of non-insect arthropods meshes nicely with entomology. As entomologists, it is important for us to be able to identify relatives and to understand their ecological interactions. The rest of the day was full of the mighty Odonata! Starting with a series of lectures from guest speaker Steve Brooks (once again, from NHM) on the identification of British Anisoptera (dragonflies) and Zygoptera (damselfies). The afternoon was spent gleefully identifying odonatans using their larval exuviae with The British Dragonfly Society’s Shropshire County Recorder, Sue Rees Evans!

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The larval exuviae of the Southern Hawker (Aeshna cyanea). Dragonfly larvae are predatory and possess a labial “mask”, a modified labium tipped with pincers. The mask is fired out to grab and immobilise prey. 

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The larval exuviae of a damselfly. The appendages on the rear are called lamellae and they aid gas exchange.

With Odonata checked off the list, we had a day dedicated to an assortment of insect orders with Dr. Mike Copeland. To name a few, we covered the Phasmida, Dermaptera and Neuroptera. The following day started off with a practical session in which we unleashed the fury of lacewing larvae onto some chubby mealybugs; a little taster of what is to come in the Commercial & Practical Biological Control module!

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A lacewing larvae chowing down on a mealy bug. They are voracious predators with specialised mandibles used to extract the bodily fluids of their prey.

The module and week ended on a mellow note, with another chill session of pinning and curation. Practice makes perfect!

Module 3: Experimental Design & Analysis

Being able to design an experiment to test a hypothesis and then analysing the acquired data using the appropriate statistical analyses, holds fundamental importance in science. Once again, the course is full of people with varying levels of experience in different areas, and statistics is no exception. The module reinforced the importance of a robust experimental design, and introduced the cohort to the statistical software R and how to run a range of tests using it. Of course, I would rather have fun practicals over this in a heartbeat, but you can’t replace bread and butter with more filling and expect to have a sandwich! Having just finished this module, we start the Commercial & Practical Biological Control module on Monday! *crowd cheers* HUZZA!!

Soooooo…that’s it from me for now! Linzi will be posting an article on Tuesday on insects which survive in extreme environments and their adaptations to the hostile conditions they live in.

Until next time!

 

By Aqib Ali  (Twitter:@EntoAqib , Email: Aqib1996@hotmail.co.uk , Linkedin: Aqib Ali)

MSc Entomology Twitter: @EntoMasters