Larval Aggregation Affects Feeding Rate in Chlosyne poecile (Lepidoptera: Nymphalidae)

Abstract

Larvae of Chlosyne poecile (Felder) (Lepidoptera: Nymphalidae: Melitaeini) on Razisea sp. (Acanthaceae) feed in large aggregations as early instars but disperse and feed in small groups or as solitary caterpillars in later instars. The effect of group size on per capita feeding rate was tested by manipulating the number of larvae on a leaf and measuring the leaf area eaten in short-term feeding trials. Feeding rate increased significantly with group size for first instars but decreased with group size for all larger instars. Although feeding rate decreased significantly with group size for second instars, second instars in the field were usually found in large groups and did not begin to disperse until the third instar. Variance-to-mean ratios indicate that larval aggregation was lower in later instars, slowly approaching a random distribution. The distributions of larger instars may therefore be the result of random dispersal to food and not the active avoidance of other larvae. If the observed lag between the predicted optimal time to disperse and the observed pattern is adaptive, then it may be due to unmeasured benefits of aggregation, such as lower predation rates and unmeasured costs of dispersal. Egg clustering and aggregation of larvae may be more common for butterflies in the Neotropics than in other areas.

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