Interview with a Social Insect Scientist: Eric Darrouzet

Eric’s article, where he and his co-authors analyzed whether beehives face predation threats from more than one hornet colony (Vespa velutina nigrithorax), using both hydrocarbons and microsatellites, can be found here.

IS: Who are you, and what do you do?

ED: I am an associate professor at the University of Tours, where I serve as director of the Agrosciences Department (one of the university’s teaching departments). I am also a researcher at the Research Institute for Insect Biology (IRBI; UMR CNRS 7261). I mainly study chemical communication in eusocial insects, such as hornets, termites, bees, and ants.

Dr Eric Darrouzet is associate professor in the University of Tours (France). He manages a team in the Research Institute for Insect Biology (UMR CNRS) to work on the Asian hornet Vespa velutina nigrithorax.

IS: How did you develop an interest in your research?

ED: Early on, I studied reproductive mechanisms in parasitoid wasps and quickly moved into analysing the chemical cues that females use to maximise reproduction. Within a few years, I became interested in eusocial insects, given that chemical communication is probably the most important structuring force in their societies. My initial work was with termites (Reticulitermes species). In 2007, I got interested in an invasive eusocial insect that had arrived in France just 3 years prior: the Asian hornet (Vespa velutina nigrithorax).

I was convinced that studying chemical communication (e.g., chemical signatures composed of cuticular hydrocarbons, alarm pheromones, sex pheromones) could help develop targeted and efficient systems for controlling this invasive species. Moreover, as very little was known about this hornet, it was possible to answer numerous biological and ecological questions about it and other hornet species.

A hornet nest

IS: What is your favorite social insect, and why?

ED: Hornet species, of course! In all seriousness, every social insect taxon is exciting to research. There are so many topics to study in insect societies, like nest architecture, communication systems, social structure, and how females become queens, just to name a few examples. At present, I am very interested in hornet species. This group was relatively little studied in the past, and so many scientific questions remain to be explored.

IS: What is the best moment/discovery in your research so far? What made it so memorable?

ED: That is a difficult question. However, when I discovered a parasite (Conops vesicularis) that could kill Vespa velutina foundresses (Darrouzet et al, 2015), that was a great moment. It happened like this: I was dissecting queens to show a colleague what their reproductive tracts look like. I was quite puzzled to observe a white mass in one of their abdomens because it was the first time I had observed such a structure. It turns out that it was a parasite! We demonstrated that this local species, a parasitoid fly, can parasitise and kill Asian hornet foundresses as colonies are getting started.

A hornet worker of the invasive species in Europe, Vespa velutina nigrithorax.

IS: Do you teach or do outreach/science communication? How do you incorporate your research into these areas?

ED: I regularly do outreach to share information about social insects, their nests, and the invasive hornet V. velutina (its biology and ecology; its impacts on biodiversity, our economy, and our health; and potential control strategies). My most common audiences are students, beekeepers, everyday citizens, and journalists. Sometimes I will draw on my own work to develop points made during these outreach efforts.

IS: What do you think are some of the important current questions in social insect research, and what’s essential for future research?

ED: In science, all questions are important and interesting. Because it is my field of specialty, I think it is essential to analyse communication systems in social insects. Communication is the link among all the individuals making up a group, such as a colony. Sociality can only exist because those individuals are communicating.

Moreover, by analysing communication systems, we can come up with better ways for controlling insect pests, including invasive species. For example, we can develop specific baits to improve trapping systems, synthetic pheromones to disrupt reproduction, or repulsive compounds to drive away specific species, like agricultural pests. Gathering knowledge about insect chemical communication is crucial to this work.

A member of the Hornet Team is collecting hornet workers in predation in front of a hive.

IS: What research questions generate the biggest debate in social insect research at the moment?

ED: What a difficult question! Whatever the scientific domain, you wll find debates around specific questions. Inf I focus on my area of expertise – chemical communication in insects – I question the function of every chemical compound in a pheromone blend. Is it that each compound possesses a specific function or that a mixture containing a particular relative quantity of these compounds givesrise to a function? One challenge is also linked to our technical capacity to identify all the compounds present. Maybe compounds present at low levels could have an active role in the pheromone blend. However, when we are cmparing blends among individuals, it is difficult (or impossible) to analyse all the compounds present. So, in general, we focus on the main compounds so that we can obtain several fundamental pieces of information. That said, we are left wondering what insects are actually perceiving. Is it the main compounds in the pheromone blend, or all of the compounds in the blend, including those present at very low levels? It is a difficult but interesting question! I think that if there are so many compounds present, each compound must have a function. But what function is that? The question remains open.

IS: What is the last book you read? Would you recommend it? Why or why not?

ED: The last book I read was written by a colleague at my university: Le bateau de Palmyre, quand les mondes anciens se rencontraient (The Palmyre boat, when ancient civilizations met”) (Éditions Tallandier). The author, Maurice Sartre, presents what we know about travel and exploration by ancient civilizations. He shows that global trade existed thousands of years before modern times…and that humans probably faced the same problems as we do today with regards to invasive species.

A hornet nest was collected in a tree.

IS: Outside of science, what are your favorite activities, hobbies, or sports?

ED: I am fascinated by ancient civilizations. I have read books about Mesopotamian and Egyptian civilizations, for example. It is amazing to see what these peoples built, how they lived, and what their cultures were like.

Since I study V. velutina, I am in contact with several beekeepers, and some have become friends. Consequently, I was inspired by them to try beekeeping myself! I have my own apiary, which I got started one year ago. It is extremely interesting. I spend a lot of time observing the workers’ activities and managing my colonies. Producing my “own” honey is also fantastic! What’s more, I now have my own experimental site, right there in my garden, where I can test traps targeting V. velutina, which preys on bees.

IS: How do you keep going when things get tough?

ED: Doing scientific research is always difficult. We have to keep at it, trying things again and again. I remember my PhD advisor telling me that research is 90% failure and 10% success. So, challenges are a normal part of the job.

A bee hive is attacked by some hornet workers. The honey bees are stressed and stay at the hive entrance to defend their colony.

IS: If you were to go live on an uninhabited island and could only bring three things, what would you bring? Why?

ED: First, I would like to bring my family. My wife and children are what is most important in my life. The second would be books. I have so many books at home, and knowledge is extremely important to me. Therefore, I would bring scientific books, technical books (we would need to figure out how to survive on that island!), and literature.

IS: Who do you think has had the most considerable influence on your science career?

ED: A scientific career is influenced by so many people and colleagues. Choosing a single person is really hard. My high school biology teacher had the earliest influence on me, and she is the reason that I studied biology in college. Next, I would probably say my PhD advisor, who taught me how to be a scientist, how to think, how to implement scientific protocols, and how to rigorously approach scientific results, among other things.   

A honey bee colony could be attacked by a lot of hornets. In this example, 20 to 30 hornets were in predation. The colony was greatly impacted by the predation pressure and was killed in few months.

IS: What advice would you give to someone hoping to be a social insect researcher in the future?

ED: It is hard to become a scientific researcher these days. If speaking to a motivated student, I would say: choose and work with a good scientific lab and team during your PhD. This team should be publishing regularly. You need to learn different techniques and publish several articles to have a chance at obtaining a position. However, the best advice I could give to young people is to listen to themselves: think hard about how you feel about your potential dissertation topic, research lab and team, and, most of all, PhD advisor. You are committing to 3 years of work!   

IS: What is your favorite place science has taken you?

ED: Thanks to my job, I have had the opportunity to travel to different countries. For example, I was lucky enough to go to China twice for a scientific collaboration. My collaborators and I conducted research on the viruses exchanged between honey bees and hornets. It was a fantastic project. Thanks to my Chinese colleague, Dr Chunsheng Hou, I learned about apiaries in China, different hornet species, how some companies rear hornets, and practical applications involving hornets (e.g., food, traditional medicine, pest control). Scientifically, it was very thrilling. Moreover, I was able to make one of my dreams come true: I took a walk along the Great Wall!

A hornet worker killed a honey bee. The hornet collects only the thorax to feed the larvae in its colony.

Introduced species and the olfactory landscape of foraging

By Ros Gloag

A blog post about the work of the Insectes Sociaux’s 2021 Best Paper Award “Australian stingless bees detect odours left at food sources by nestmates, conspecifics and honey bees”, by Rosalyn Gloag, Jordan P Smith, Ruby E Stephens, Tim A Heard and Madeleine Beekman, Insect Soc 68:151–159.

My colleagues and I received a lovely email this month to tell us that our paper had been selected for the Insectes Sociaux Best Paper Award 2021 by the Editorial Board. We couldn’t be happier to know that Australia’s amazing stingless bees are getting a bit of a spotlight!

This project arose from the combination of two lines of questioning. The first was a desire to better understand how Australian stingless bees (Tetragonula spp and Austroplebia spp) recruit their nestmates to profitable food sources. When people think of nestmate recruitment in social bees, they are likely to think of the famous waggle dance of honey bees (Apis sp.). Honey bee foragers encode information on the location of food sources in a dance, which they perform inside the darkened nest to their sisters. Stingless bees, meanwhile, have no special dance and yet are nevertheless very efficient recruiters. How do they do it? Studies of stingless bee species in South and Central America have shown that they regularly use pheromones or other odours at, or near, food sources to help guide nestmates to food. There is a relative dearth of information, however, about the recruitment mechanisms used by stingless bees in other parts of their global tropical distribution.

Honey bees and Tetragonula clypearis feeding at an artificial feeder (not as part of the study discussed here, but this photo still illustrates nicely their willingness to co-feed and the relative size of each species! (photo. R. Gloag)

Our second line of questioning involved the possible impacts of introduced bees on native bees in the ecosystems they invade. In Australia, honey bees are not native. They were brought to the continent in 1822 for beekeeping, and later naturalized throughout Australian bushland. In recent years, I have spent a lot of time studying feral Apis populations in Australia and a common question from the public is whether honey bees here impact native bees in any way. I always explain to them that scientists are very interested in this too, but that it is not an easy question to answer because any impacts are likely to be indirect (e.g. competition for resources or nest sites). Honey bees today are hugely abundant in Australian ecosystems and it is common to see them foraging on the same flowers as stingless bees and other native bees. We know that bees can detect the odours of sympatric species at flowers when foraging, but does this apply also to cases where one species is a recent invader? Do Australia’s native bees either avoid or prefer flowers that carry the “whiff” of a honey bee? If so, this could be one avenue by which introduced Apis indirectly affect the foraging ecology of native bees.

We decided to test this idea with very simple binary choice trials (see Figure 1 from the paper). In these trials, foraging stingless bees must choose between identical feeders: one of which has been previously used by other bees (that is, walked all over and potentially odour-marked) and one of which is unused (that is, clean of any bee odours). The first trials were completed in Tetragonula carbonaria by Jordan Smith as part of his undergraduate Honours project (just one of the great things he did – the other was to estimate the species foraging range here). These first trials were very interesting, clearly we needed to continue.

The beautiful spiral brood comb of Tetragonula carbonaria, one of Australia’s endemic stingless bees. (photo. R. Gloag)

Over the next few field seasons, I continued with additional trials. Ruby Stephens lent a hand once she had wrapped up her own Honours project (a great study of nestmate recognition in T. carbonaria – find it here). Progress was not fast; there were interruptions for maternity leaves, new jobs, COVID. Eventually though we had an analyzed dataset for three species of Australian stingless bee (Tetragonula carbonaria, Tetragonula clypearis and Austroplebia australis – representing the three major clades of stingless bees in Australia) each tested in foraging choice trials against the odours of nestmates, non-nestmate conspecifics and honey bees. All three species preferred feeders previously used by other bees, even honey bees, consistent with being able to detect food-marking odours and use these in their foraging decisions. We also tested two of the species (T. carbonaria and A. australis) in choice trials offering feeders marked with vanilla vs no-odour and found no forager preference, indicating it is not simply that stingless bees prefer the smelliest feeder, or that they are attracted to all novel odours.

So stingless bees in Australia use odours at food sources as part of their recruitment strategy, just like their Neotropical relatives. Those odours might be either pheromones, chemical “footprints” or a mix of the two. They also can detect and respond to honey bee odours (almost certain to be footprints in that case). What does it mean that stingless bee foragers were attracted to food sources marked with honey bee odours? My view is that it shows that stingless bees are highly adaptable foragers that can readily learn that any particular odour signals food. I suspect responses to honey bee odours might differ in different contexts, though this remains to be tested. Certainly we are left now with a whole range of new questions: How does the ability to detect the odours of introduced species impact native bee foraging in natural contexts? Do honey bees also respond to the odours of stingless bees? More broadly, how do social insects respond to the pheromones of introduced species that share their ecological space and trophic level?

We thank again the Insectes Sociaux Editorial Board for bestowing on this study the Best Paper 2021 Award, and look forward to learning more about stingless bee foraging ecology in the future.