EXPERIMENTAL TESTS OF THE MECHANISM FOR ANT-ENHANCED GROWTH IN AN ANT-TENDED LYCAENID BUTTERFLY

In a previous laboratory study, larvae of the ant-tended lycaenid butt erfly Hemiargus isola developed into larger adults when reared with th e ant Formica perpilosa than when reared without ants. Ants neither fe d butterfly larvae nor significantly delayed developmental duration. W e investigated two non-exclusive hypotheses for the mechanism of this effect: larvae tended by F. perpilosa (1) consume more food, and (2) d igest the food they consume more efficiently, than those reared withou t ants. Larvae reared in the laboratory with F. perpilosa ants became significantly heavier adults but produced a significantly lighter feca l mass than their untended counterparts, suggesting that greater food consumption was not the primary mechanism for the higher growth rates of ant-tended larvae. Tended and untended larvae were equally proficie nt at digesting the contents of pollen (a major natural food source) t hroughout the tended portion of the life cycle. Taken together, the re sults suggest that neither greater consumption nor higher assimilation accounts for the larger size of F. perpilosa-tended larvae. We propos e that tended larvae may expend less energy than their untended counte rparts.