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.

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An extensive electrophoretic survey of enzyme and protein markers was conducted for a haplodiploid eusocial insect, the red imported fire ant (Solenopsis invicta), and for a diploid communal insect, the eastern tent caterpillar (Malacosoma americanurn). This survey resulted in the discovery of 110 electrophoretic loci for S. invicta (15 of which were polymorphic at the 95 per cent level) and 37 electrophoretic loci for M. americanum (seven polymorphic). Expected heterozygosities (mean Hexp S.E.) were 0.05 1 0.013 and 0.092 0.030 for S. invicta and M. arnericanum, respectively. Although these values do not differ significantly, they are consistent with the frequently reported pattern of low gene diversity in the eusocial Hymenoptera relative to noneusocial diploid insects. This pattern persists when a large number of markers is scored in different life stages and castes, as in S. invicta in this study, and when a direct comparison is made using data generated in a single laboratory.

Animal social groups often consist of non-relatives, a condition that arises in many cases because of group merging. Although indirect fitness contributions are reduced in such groups compared with those in groups composed of close kin, the genetic-heterogeneity hypothesis suggests that these groups may benefit from increased intracolony genetic variation, which may boost group performance through increased task efficiency or parasite resistance. We confirm one prediction of the task-efficiency explanation by demonstrating a genetic basis for task thresholds of socially important behaviours in eastern tent caterpillars. However, we found no evidence that the expanded range of task thresholds in mixed colonies translates into improved individual or colony performance in the field. By contrast, increased group size, a less commonly considered correlate of group mixing, was found to enhance individual fitness through its effects on larval growth. We conclude that fitness benefits offsetting the dilution of relatedness in heterogeneous social groups may often stem from augmented group size rather than increased genotypic diversity.