by Sofia Gomes and Ana M. Camargo
Ragwort is one of the main focal plant species that we use in our group to study insect-plant-microbe interactions.
Recently, we have also started studying the bacterial communities of the caterpillar Tyria jacobaeae, a specialist herbivore of ragwort. We found a few dominant taxa that were present in all three locations that were sampled, but the majority of (low abundant) bacteria in these caterpillars resembled the local soil microbiome. Of course, lots of questions remain. What do all these bacteria do? Which ones are important, and for what? How can these caterpillars maintain a constant dominant bacterial composition when caterpillar’s guts are often described to be inhospitable environments for microbial growth? All these interesting questions and more can be asked in this system. But, we are missing the one very important thing that we need when diving into this: the ability to manipulate the microbes in the caterpillars! Working with field collected caterpillars does not allow us to standardize experiments, and we need to do so to be able to ask these relevant questions.
This was when Ana, the entomologist in our team, started wondering whether it would be possible to rear T. jacobaeae on artificial diet. Unfortunately, the words of advice indicated that this would probably be a very hard job, as T. jacobaeae is not considered to be amenable for rearing out of ragwort plants. But this didn’t discourage her. On the contrary, in 2020 Ana collected all the caterpillars she could find in the field and brought them to the lab, where she reared them on ragwort plants until the pupa stage. These pupae were stored in the cold, as this species requires a cold period to complete metamorphosis. After spending some months in the cold, the pupae were transferred to a warmer temperature, and the emerging adults introduced in cages with ragwort plants for mating and oviposition. The many eggs that were laid hatched into larvae that developed well on the ragwort plants and pupated around a month later. These pupae were also stored at 4ºC for around 8 months. This way, a culture was established in the laboratory, so that we now have adults and larvae when we need them. However, the rearing still relied on ragwort plants. About a month ago, Ana decided to start some tests with artificial diets. A first check was done to see if this population had made it through their second “winter”, and we were all happy to observe an emergence success of 100% of the pupae moved out of the cold!
A week after the introduction of the first adults, a high number of eggs had been laid on the leaves of the plants, and around a week after the first eggs were noticed we saw the first neonates. These larvae will now be reared in different semi-artificial diets containing ragwort material, and we all have our fingers crossed for the caterpillars to be able to feed and develop on them! This will be an important step to ease up our research on Tyria jacobaeae microbiomes.