Foraging in nature by larvae of Manduca sexta - influenced by an endogenous oscillation

Foraging by larvae of the moth Manduca sexta was studied in the field on th e native host plant Datura wrightii. Continuous observation of individuals revealed that larvae moved very little, but fed for approximately one third of the time, independent of temperature or photoperiod, although the large r ones fed for the longest times. They were indiscriminate with respect to the part of plant fed upon, and analysis of feeding bouts and interbouts in dicated that the pattern of feeding was not strongly influenced by direct n utritional factors. Attacks by parasitoids had a significant impact on feed ing behavior. All individuals showed strong regularity in the times when fe eding was initiated, and analyses demonstrated that feeding was initiated a t times corresponding to fitted oscillation periods of approximately 4 min. Feeds were not initiated on every peak, but at times corresponding to the primary period, or harmonics of it. The period was not influenced by temper ature, was different for all individuals, and was asynchronous among indivi duals. We conclude that an endogenous neural oscillation underlies the rhyt hm, and strongly influences the overall pattern of foraging. We discuss the oscillation in terms of its possible ecological significance, particularly the need for vigilance. (C) 2000 Elsevier Science Ltd. All rights reserved .