Group size effects on survivorship and adult development in the gregarious larvae of Euselasia chrysippe (Lepidoptera, Riodinidae)

Caterpillars living in aggregations may derive several benefits that outweigh the costs, including better survivorship and improved growth rates. I tested whether larval group size had an effect on these two vital rates in Euselasia chrysippe. These caterpillars feed gregariously during all instars and move in processionary form over the host plant and even pupate together. There was a positive relationship between group size and larval survivorship in the field, although genetic variability was not taken into account in this experiment. Under laboratory conditions, there was also a positive relationship between group size, and larval growth rate and adult weight. This supports the hypothesis that aggregations facilitate feeding and larval growth. Single sixth instar larvae in the laboratory also had a lower survivorship than larvae in groups. These results provide further evidence of the benefits of group living for gregarious caterpillars.