Carlos Bustos‐Segura: do herbivore parasitoids help plant fitness?

What’s your paper about?

In this study we explored whether parasitoids of herbivores are beneficial for different components of plant fitness. First, we found that parasitoids reduce plant damage and improve plant reproductive traits, since plants flowered faster and produced more seeds when leaf caterpillars were attacked by parasitoids. In addition, we looked at the interaction between seeds and the beetles that feed on them. We found that caterpillars induced resistance against seed beetles whether or not they were parasitised. We also looked at the parasitoids of these beetles, but did not find any effect of leaf herbivores or their parasitoids on them. Thus, the interaction with both herbivores and parasitoids is globally beneficial for plants, since they produce as many seeds as when they are not damaged, but those seeds are better protected against seed beetles.

How did you come up with the idea for it?

Previous studies in our group indicated that parasitoids of herbivores were important for lima bean plants. However, at the same time herbivores can provide some benefits to plants by inducing resistance against seed beetles. One possibility was that parasitoids would inhibit this induction, which would introduce contrasting effects in the indirect interaction between plants and parasitoids. We wanted to figure out what was actually happening and we decide to settle this experiment.

How is your paper new or different from other work in this area?

We integrated different aspects of plant-insect interactions in the same study within a multitrophic context. From one side, the immediate effects of parasitoids on plant damage and reproduction and, from the other hand, how parasitoids indirectly affect other interactions in the system. In this case, the interactions between seeds, beetles and their parasitoids. Our study takes into account how interactions at different times and trophic levels affect the plants, a bit closer to what happens in nature. In addition, we explored how herbivores and plants can mediate the indirect interactions between organisms of the third trophic level, which has been rarely done in experimental studies.

About the research

What is the broader impact of your paper?

With this study, we have evidence that from the plant perspective it is beneficial to interact with a complex associated insect community, even if that means receiving some insect damage. Since in other systems it has been found that herbivores parasitoids reduce plant damage, and herbivores induce resistance against future herbivores, it is likely that in other systems something similar is happening. This has very interesting implications for agriculture, since there are some benefits of biological control that have not been taken into account. In addition, for the general ecological theory it provides more information about how different trophic levels influence each other in direct and indirect ways.

Did you have any problems setting up the experiment or gathering your data?

It was a very challenging experiment since we had to control several things during the season, while simultaneously allowing plants and the insect community to interact naturally at specific times. This required a lot of knowledge on the natural history of the several species that were involved. For example, we had to stablish colonies of parasitoids and caterpillars in the field lab; meanwhile we prepared the field and grew the plants. We would need many insects for specific times but with good teamwork, we managed to synchronise the plant development with the insect colonies, which required coming back from the field, skipping resting and rear insects every day. Another issue was that we could not collect the seeds when they were just mature, since we know that beetles and their parasitoids interact with them a bit later. However, when the seedpods of lima bean dry up, they burst and release the seeds several meters away. Thus, we had to develop a method to save the seeds from each plant separately and still expose them to the naturally occurring community in the following weeks. We made bags for collecting the seeds from each plant, but the bag mesh should allow the different insects to enter the bag and the seeds to stay inside. We tried it up in the field and it worked!

What are the big questions still to answer?

There are big questions to answer. For example, how plant volatile production might affect the indirect interactions between insects separated in time; whether there is potential for selection among insects that interact indirectly; and we still need to integrate the effects of the animal community on different species of plants that are in competition. It will be so exciting to see the coming developments and keep on contributing with other studies.

About The Author

How did you get involved in ecology?

I had always loved plants and insect, and other animals too. It made all sense after I tried neurobiology, which I am still fascinated with, but I found out that I did not enjoy spending everyday indoors in the lab. With that background, I was wondering how animals find their food, recognise poisonous plants and manage to survive in the wild, and that led me to wonder how plants react to this. When I started rearing insects for experiments, I remembered that as a kid I would take scorpions, ants, wasp nests etc. inside home and try to rear them in my bedroom, but would not understand why someone would think it was rare. Thus, I think it has been a natural way for me.

What are you currently working on?

At the University of Neuchâtel with Prof. Betty Benrey we are finishing up some projects related to plant diversity, effects of herbivore timing on plant responses, host and host plant effects on parasitoids and effects of plant domestication at different trophic levels. After this, I will start working in a project about defences in cotton plants with Prof. Ted Turlings.

What is the best thing about being an ecologist?

You get to work directly with the organisms in a natural system. It is fascinating trying to answer questions about how nature works and at the same time designing new ways for manipulating specific factors without transferring everything to the lab. You get the chance to know cool places, travel around, and work with nice people. If you like maths and stats, there is a lot of things to do there, and of course we also do lab work. So, no time to get bored.

What is the worst thing about being an ecologist?

Sunburn, mosquitoes… In the field site we work in Mexico, the heat can be quite exhausting. After some hours under the sun, the sunscreen and sombrero do not work that much and then, one prefers to spend the rest of the evening hiding from the sun even if there is a nice beach around. I do not mind mosquitoes too much, but dengue, zika and chikungunya are getting more common in the area, so we have to be more careful with that.

What do you do in your spare time?

I like biking, hiking, playing bass guitar… and after working in the greenhouse, I still like to grow more plants in my house.

One piece of advice for someone in your field…

Never leave the notebook in the field.

Read the paper in full here or the plain language summary here.

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