ALLOCATION OF LIQUID FOOD TO LARVAE VIA TROPHALLAXIS IN COLONIES OF THE FIRE ANT, SOLENOPSIS-INVICTA

In social insects, the size, caste and reproductive capacity of adults is determined in part by nutrition during larval development. Among ants, workers bring food to immobile larvae, giving workers potential control over larval nutrition, and making social feeding a potential mechanism of individual and colony ontogeny. During each regurgitation (trophallaxis), workers feed larvae the same, small increment of liquid food, regardless of larval attributes and conditions. Therefore, differences in the total volume of food ingested by larval resulted from differences in the rates of trophallaxis to them, not from differences in the durations of trophallaxis. The rates of worker-to-larva trophallaxis (feedings/h) were examined to investigate the mechanisms by which liquid food is allocated to larvae by workers. The rate of trophallaxis increased with larval food deprivation. The magnitude of this increase depended upon the larva's size. When larvae were food-deprived, larger larvae were fed at significantly higher rates than were smaller larvae (13 feedings for each mu l of larval volume). Once larvae of all sizes were satiated, workers fed them at similarly low rates. Regardless of size, larvae required about 8 h of feedings to reach satiation; that is, small larvae did not become sated any sooner than did medium or large larvae. Rates of trophallaxis were independent of: (1) the size or hunger of adjacent larvae, (2) rates, of larval encounter by workers (larvae were encountered hundreds of times per h but were fed only tens of times); (3) larval location on the brood pile (top or bottom); and (4) larval body orientation (mouthparts up or down). These results provide the first quantitative evidence that an individual larval hunger cue directs the feeding of each larva, and that the strength of this cue, and therefore the feeding rate, varies with larval size and hunger. (C) 1995 The Association for the Study of Animal Behaviour