Behavioral and developmental homeostasis in the fire ant, Solenopsis invicta

The von Bertalanffy rule (1960) predicts that low incubation temperature du ring larval development will result in larger adult body size. If larval de velopment in social insects followed this rule, then low incubation tempera ture would induce the development of larger workers and possibly even sexua ls. To test this prediction, the effect of incubation temperature on larval development, larval meal size, larval tending and worker recruitment to fo od in the fire ant, Solenopsis invicta was investigated. Temperatures teste d where within the range at which brood remains viable. Contrary to the predictions of the von Bertalanffy rule, worker size was un affected by incubation temperature, and sexuals were reared at the high rat her than the low incubation temperature. Moreover, larval meal size, the ra te of larval tending by workers and the total number of workers recruited t o food were unaffected by temperature. Mechanisms regulating developmental and behavioral homeostasis were as foll ows: the duration of larval development and the rate of larval growth chang ed proportionately with temperature such that the mean and variation of pup al size was unaffected by incubation temperature. Larvae solicited at the s ame rate, swallowed at the same rate and swallowed for the same duration su ch that meal size was unaffected by incubation temperature. On the brood pi le, fewer workers tended brood at higher incubation temperatures, but worke r tempo increased; as a result, brood tending was not adversely affected by incubation temperature. The rate of worker recruitment to food sites outsi de the nest increased with temperature, but the duration of the recruitment effort decreased such that, over time, the same total number of workers wa s employed to retrieve food. Incubation humidity was also investigated. When brood chambers were less th an 100% humid, workers recruited to food and tended larvae (retrieved, sort ed and groomed them), but did not feed larvae. Eventually, larvae died of s tarvation and were cannibalized. (C) 2000 Elsevier Science Ltd. All rights reserved.