Activity Patterns, Body Temperature and Thermal Ecology in Two Desert Caterpillars (Lepidoptera: Sphingidae)

Abstract

The activity patterns, body temperatures, microhabitat characteristics and feeding behavior of larvae of two sphinx moths which inhabit the Mojave desert were investigated. Hyles lineata occurred in association with and fed upon a variety of desert annual plants; Manduca sexta was associated with only one plant species, Datura metalloides, a perennial. Body temperatures of H. lineata were relatively constant over a wide range of air temperatures; body temperatures of M. sexta approximated the air temperature for most of the day. Elevated T_b was associated with exposure of the larvae to direct solar radiation and high ground temperatures. Hyles lineata regulated T_b by orienting with respect to solar radiation and exploiting thermal heterogeneity in its microhabitat. Manduca sexta was shielded from solar radiation and thermal reradiation by its foodplant and never voluntarily spent time on the ground. Feeding and locomotor activity in both species were reduced during periods of both high and low air temperatures but were not related to time of day. Upper lethal temperature in saturated air was 45 degrees C for both species. Feeding rates were strongly dependent on body temperature in both species. Hyles lineata is a generalist, utilizing a variety of energy resources; the occurrence of M. sexta in the desert may depend on the presence of a single plant species, the jimson weed.