Plasticity in foraging patterns of larval colonies of the small Eggar moth, Eriogaster lanestris (Lepidoptera: Lasiocampidae)

Abstract

Activity patterns of colonies of the central-place foraging (CPF) social caterpillar, Eriogaster lanestris, were electronically long-term recorded under field conditions. Caterpillars showed distinct, highly synchronized activity bouts during which they left their tent, fed on their host-plant and returned to their tent. Caterpillars stayed almost inactive during their digestion phases when they rested inside or on the tent. The number of daily foraging bouts varied over a wide range. On warm and sunny days with high solar irradiation caterpillars left their tent up to 9 times, whereas there was only one foraging bout on cool and rainy days. On average, 4.8 daily foraging bouts were performed by fourth (pre-final) instar larvae, which is higher than the number reported for another well-known CPF species, the eastern tent caterpillar Malacosoma americanum. Overall, E. lanestris colonies required 31±2 foraging periods to pass their fourth instar within 7.3±1.2 days under the temperature conditions prevailing over the course of our experiment. The length of individual foraging bouts as well as the phase of digestion proved to be strongly temperature dependent. In contrast to patterns reported for M. americanum, foraging activities were not bound to specific times of day and also continued during night time if temperature permitted. Changes in light phases only had a modulatory effect on the onset of the next foraging bout. E. lanestris is the first lepidopteran species with CPF social caterpillars reported to show a plastic, but nevertheless strictly synchronized foraging pattern. Caterpillars are thus able to optimize their food intake and enhance growth during periods of thermally favourable conditions while minimizing their exposure to natural enemies.