In this blog post, we’re getting stung with knowledge on the fascinating responses to temperature shifts in the Map butterfly (Araschnia levana). From their new paper: “High Nitrogen loading impacts the temperature-size rule and heat tolerance in a nettle-feeding butterfly”, author Berber Meulepas shares insights behind their project work with the Map butterfly and its associations with the common stinging nettle (Urtica dioica). Berber discusses the painful side of fieldwork (a hazard of working with nettles in the field!) and reiterates how temperature sensitive insects can be.
About the paper
In this paper we try to answer how caterpillars of the map butterfly (Araschnia levana) respond to rising temperatures and shifts in nutrient-balances in their diet. This research is part of a bigger project, where I try to understand how herbivorous insects respond to the (synergistic) effects of climatic warming and nitrogen pollution, using nettle-feeding butterflies as a model system. Within the nettle-feeding butterfly community we are observing diverging trends between species in abundances in Europe, despite sharing the same host-plant.
In this experiment we looked in more detail at specific responses in caterpillar development and adult heat tolerance to elevated rearing temperature and host-plant quality, using the map butterfly (Araschnia levana). The main take home message from our findings was that both temperature and host-plant stoichiometry affect butterfly performance, with warming and balanced plant nutrition enhancing growth, development, survival and adult heat tolerance. Moreover, we found a trade-off between size and age at maturity whereby individuals either matured rapidly at smaller sizes, or more slowly at larger sizes. Importantly, this trade-off only emerged under favorable, fast-growth conditions, suggesting that developmental times become the key limiting factor determining final body size in these environments.
We further show that host-plant nutrient imbalances can mediate how insect herbivores prioritize between size and age at maturity under warming conditions, with consequences for their ability to cope with thermal stress later in life. In a broader context, this research highlights how global change drivers, such as nutrient enrichment from human activities and rising temperatures, do not act in isolation, but interact to shape how organisms grow, develop and survive.
About the research
In order to collect the data, we reared caterpillars of the Map butterfly in climate chambers in the greenhouses of the Radboud university in Nijmegen (NL). Before setting up this experiment I had never reared caterpillars by myself before, so that was a challenge to begin with. I learned a lot by reading blogs and watching videos on rearing butterflies. We went out into the field, and once we caught the adult butterflies and provided them with fresh flowers and their hostplants, all we could do was wait and hope they laid eggs. Luckily, they did! The map butterfly lays its eggs in a very specific way: They lay vertical pendant strings of up to 15 eggs, hanging from nettle leaves (see figure 1). It is said that they do this to confuse predators.
Another ‘challenge’ was working with the nettle plants. Stinging nettles grow very easily, so that was not the problem. However, as their name suggests, they sting! As I had to feed the caterpillars multiple times per day, and had a lot of containers to feed, it took too much time to wear protective gloves as you lose some dexterity and fine tactile sensitivity in your fingers, making precise handling more difficult. This meant that during the months I was running the experiments, I stung my fingers so many times on the nettles, that they became almost constantly numb between feeding sessions.
Since the end of this experiment, we have continued rearing other nettle-feeding butterflies and dove further into host-plant quality and effects of fertilizer on C, N and P concentrations in nettle leaves.
About the author
I got into ecology through my bachelor studies, but especially after following a field course to the island of Terschelling. From that week on I knew I wanted to pursue insect ecology, and after I got lucky enough to since be involved in that same course for the past 7 years, I’ll be taking over coordination next year! After my masters I applied for an FWO PhD grant, and am currently 1.5 years into my PhD project.
Within the project I am working with long term butterfly monitoring data of four nettle-feeding butterfly species in order to understand the diverging patterns in species abundance within the nettle-feeding butterfly community. Additionally, I have recently performed a Europe-wide field campaign on the Common stinging nettle (Urtica dioica) with the help of many enthusiastic volunteers across the butterfly monitoring network.
Right now, as spring is here, my favorite thing to do is going on long hikes and camping outside. But I also do not mind reading a good book, or organizing dinners with friends. I am very excited about this paper coming out, especially as it is the first paper within this project.
