The Evolution of Social Behavior in Insects and Arachnids: Social evolution in the Lepidoptera: ecological context and communication in larval societies

We review key ecological and behavioral mechanisms under­ lying the origin and maintenance of larval sociality in the Lepidoptera. Using communication contexts of group defense, cohesion and recruitment as a framework we relate social complexity among gregarious caterpilla~ to three panerns of foraging: patch-restricted, nomadic, and central-place. A review ofthe incidence oflarval gregarious­ ness in the Lepidoptera demonstrates that sociality is wid"e­ spread in the order, occurring in twenty or more families representing thirteen ditrysian superfamilies, and it is likely to have evolved numerous times in response to differ­ ent selective pressures. We specifically address the role of sociality in larval defense and resource use, with a focus on (I) signal enhancement in communication systems, (2) differential larval vulnerability, and (3) ant association. Larval Lepidoptera experience the greatest likelihood of mortality in the earliest instars; larval sociality enhances defensive and resource-exploitation signals in these in­ stars, positively influencing survivorship and larval growth. Disease, predation and parasitism, nutrition, and inclusive fitness are discussed in terms ofcosts and benefits ofgroup living. Finally, we identify two areas where additional research will con tribute significantly to an understanding ofsocial evolution in the Lepidoptera: (I) comparative phy­ logenetic studies, using ecological and communicative characters to trace the origins of caterpillar societies and transitions among them, and (2) larval behavior and ecol­ ogy, focusing on kin discrimination abilities, assessment of colony genetic strucrure, and most importantly on the means and contexts of caterpillar communication.