Plasticity of collective behavior in a nomadic early spring folivore

Abstract

Collective behavior in the forest tent caterpillar (Malacosoma disstria) meets the thermal constraints of being an early spring folivore, but introduces other constraints in food choice. These are minimized by state-dependent, inter-individual, and ontogenetic variations in responses to social cues. Forest tent caterpillars use pheromone trails and tactile communication among colony members to stay together during foraging. At the group level, these rules lead to cohesive synchronized collective nomadic foraging, in which the colony travels en masse between feeding and resting sites. This paper proposes that synchronized collective locomotion prevents individuals from becoming separated from the colony and hence permits them to reap the advantages of group-living, notably collective basking to increase their body temperature above ambient and collective defense against natural enemies. However, this cohesive behavior also implies conservative foraging, and colonies can become trapped on poor food sources. High fidelity to pheromone trails leads to strong amplification of an initial choice, such that colonies seldom abandon the first food source contacted, even if a better one is nearby. The risk of this trapping is modulated both by consistent inter-individual variations in exploratory behavior and by inner state. Colonies consisting of active-phenotype or protein-deprived individuals that explore more-off trails exhibit greater collective flexibility in foraging. An ontogenetic shift toward more independent movement occurs as caterpillars grow. This leads to colony break-up as the season advances. Selection pressures facing older caterpillars favor solitary living more than in the earlier instars. Caterpillars respond to this predictably changing environment by altering their behavioral rules as they grow.

Silk drives aggregation and following in the neotropical caterpillar Mechanitis menapis (Nymphalidae: Ithomiini)

“…This experiment tested for the type of trail‐based communication observed in other social caterpillar species (Fitzgerald, ; Costa, ; Despland, ). Groups of five second‐instar caterpillars were placed on Solanum betacea plants either pre‐treated with exposure to other similar‐age caterpillars or not.…”

“…It is therefore difficult to generalize about patterns of juvenile sociality in Lepidoptera, as well as its ecological role or evolutionary history. For example, thermoregulation appears to be an important selection pressure in many of the temperate zone early spring feeding Lasiocampidae species (Despland, ). However, it probably plays a much smaller role in the many tropical caterpillars in which gregarious behaviour is observed.…”

Effect of density and species preferences on collective choices: an experimental study on maggot aggregation behaviours

“…Inter-individual variability (e.g. personality) can also affect both decision speed and accuracy (Planas-Sitjà et al, 2018) and can reduce the risk of choosing a sub-optimal option (Despland, 2013). This assumption could apply to groups composed of several species, which are frequently observed in arthropods and are known to provide adaptive benefits (Boulay et al, 2019;Goodale et al, 2020).…”

Effects of phenological synchronization on caterpillar early-instar survival under a changing climate

“…These small larvae usually have limited vision, but are often positively phototactic and negatively geotactic, and also respond to olfactory and gustatory cues (Perkins et al 2008). Many species start out cryptic, acquiring warning coloration later in development, and many others are gregarious in the early instars, becoming solitary as selection pressures change with increasing size (Despland 2013).…”