Gregariousness and repellent defences in the survival of phytophagous insects


  • Alison F. Hunter

A. F. Hunter, Biological Sciences Collegiate Div., 924 E 57th St., Univ. of Chicago, Chicago, IL 60637, USA (


Group living has both costs and benefits for plant-feeding insects, but defence against predators is the most widely acknowledged benefit. Gregarious folivores typically have warning coloration and elaborate anti-predator defences. Do these defences protect these species from predation? To see if protection from predators generally results from gregariousness, I compared the shapes of published survivorship curves of externally feeding, gregarious and solitary Lepidoptera and Symphyta. Gregarious species are less likely than solitary species to die in the larval stages. However, solitary species that have anti-predator defences do not have higher larval survival compared to gregarious species. This result, along with evidence from experimental manipulations of group size, suggests that repellent defences per se do not increase survival of gregarious larvae. Group behaviour is undoubtedly important in affecting the higher larval survival of gregarious species, but we currently cannot determine whether predator learning, dilution of risk, or rapid development contribute most to increasing survival.