Host-plant mediated effects on group cohesion and mobility in a nomadic gregarious caterpillar
Gregarious animals often live in larger groups in food-rich environments. We compare cohesion and mobility of forest tent caterpillar (Malacosoma disstria) groups on high-quality (trembling aspen, Populus tremuloides) and low-quality (sugar maple, Acer saccharum) host trees. Following pheromone trails allows forest tent caterpillars to maintain group cohesion, but can cause groups to become trapped on poor-quality food sources. Trail-following decreases in food-deprived individuals. We combine laboratory and field experiments to show that this nutritionally mediated balance between trail fidelity and exploration generates fission-fusion dynamics, leading to increased mobility and smaller group sizes on poorer quality hosts. Indeed, caterpillar groups feeding on maple spent more time in locomotion, split into smaller groups, switched feeding site more frequently and traveled farther when compared to those feeding on aspen. These fission-fusion dynamics can be explained as an emergent property of individual responses to conspecifics: Individuals drift apart in contexts where responses to cues from conspecifics are weakened. Increased mobility appears as an adaptive response that improves the chances of relocating to a superior food source, but lower group size likely decreases thermoregulation and increases predation. Finally, we show that forest tent caterpillar fission-fusion dynamics not only control the spatial distribution of individuals in a tree, but they are also linked to considerable differences in growth and mortality and therefore can play an important role in population dynamics.
Many gregarious animals split up into smaller groups when food is scarce. In many species, the behaviors by which group members stay together and follow each other are well-understood; how then do these behaviors respond to changing conditions? In particular, how does hunger drive groups to split up in response to decreased food availability? We compare mobility and group size of forest tent caterpillar colonies on good- and poor-quality host plants. These caterpillars use pheromone trails to move around together, but when hungry, they tend to leave these trails. We show how caterpillars on a poor-quality host plant are not only more mobile (presumably an adaptive response that improves chances of discovering a better food source), but they also split into smaller groups—a side effect of decreased trail fidelity that possibly exposes them to greater risks.
KeywordsAdaptive Fission-fusion Foraging Malacosoma disstria Population dynamics
We thank Jackie Peters for assisting with field work, the Morgan Arboretum staff for use of their facilities, and the Ministry of Natural Resources and Forestry of Ontario for supplying egg masses.
- Costa JT (2006) The other insect societies. Harvard University Press, CambridgeGoogle Scholar
- Costa JT, Pierce NE (1997) Social evolution in the Lepidoptera: ecological context and communication in larval societies. In: The evolution of social behaviour in insects and arachnids. Cambridge University Press, Cambridge, pp 407–422Google Scholar
- Drouin J (2007) Le comportement alimentaire d’un herbivore généraliste (Malacasoma disstria HBN) sur des assemblages foliaires de peuplier et d’érable. Dissertation, Université de Québec à MontréalGoogle Scholar
- Etilé E (2008) Comportement alimentaire de la livrée des forêts (Malacosoma disstria Hübner) sur quatre de ses plantes hôtes. Dissertation, Université de Québec à MontréalGoogle Scholar
- Grisdale D (1985) Malacosoma disstria. In: Handbook of insect rearing. Elsevier, Amsterdam, pp 369–379Google Scholar
- Krause J, Ruxton GD (2002) Living in groups. Oxford University Press, New YorkGoogle Scholar
- Kummer H (1971) Primate societies; group techniques of ecological adaptation. Aldine-Atherton, ChicagoGoogle Scholar
- Levesque KR, Fortin M, Mauffette Y (2002) Temperature and food quality effects on growth, consumption and post-ingestive utilization efficiencies of the forest tent caterpillar Malacosoma disstria (Lepidoptera: Lasiocampidae). Bull Entomol Res 92. https://doi.org/10.1079/BER2002153
- Robison DJ (1993) The feeding ecology of the forest tent caterpillar, Malacosoma Disstria Hubner, among hybrid poplar clones, Populus Ssp. Madison. University of Wisconsin, WisconsinGoogle Scholar
- Tinbergen N (1963) On aims and methods of ethology. Z Tierpsychol 20:410–433. https://doi.org/10.1111/j.1439-0310.1963.tb01161.x CrossRefGoogle Scholar