Relatedness and gregariousness in the orange-striped oakworm, Anisota senatoria (Saturniidae)

Oakworm larvae live in groups and provide a convenient model system for the study of gregarious behaviors of caterpillars. Most caterpillar groups consist largely of related individuals, so the costs and benefits of gregariousness must be considered within the framework of kin selection. In this study, we use allozymes to estimate relatedness within 11 groups of 4th-5th instar larvae. Allozyme diversity was high in four marker loci, with an average heterozygosity of H sub(exp) = 0.376 plus or minus 0.029 (SD) when frequencies were pooled over groups. We found a relatedness of r = 0.31 plus or minus 0.056, a relatively low value given that full-siblings show r = 0.5. The mean nearest-neighbor distance among plants was 4.34 plus or minus 3.48 m, and among groups it was 5.25 plus or minus 4.15 m. Within the framework of a mathematical dispersal model calibrated using observations of larval movement in the field, these values suggest that only about 4% of wandering larvae ever find new hosts, and that exchange is negligible among groups on different plants. Adult behaviors, either multiple mating or aggregation of egg clutches, are therefore probably responsible for the observed relatedness values.