Responses of Ovipositing Moths (Lepidoptera: Geometridae) to Host Plant Deprivation: Life-History Aspects and Implications for Population Dynamics

Abstract

For three species of geometrid moths with noneruptive population dynamics, physiological and behavioral responses of ovipositing females to larval host deprivation were recorded. Single substrate trials were used. Availability of adult food was also varied to manipulate physiological condition of the moths. Egg production rate decreased only weakly in the absence of host plant, whereas it was strongly influenced by adult feeding. The time from the beginning of the experiment to initiation of oviposition was largely determined by presence of suitable host. This variable, oviposition latency, was only weakly affected by nutritional status of the females. Oviposition rates also remained lower on unsuitable hosts after oviposition was initiated. This indicates that the effect of inferior oviposition substrate was not limited to postponing oviposition. Host deprivation and adult feeding both lead to accumulation of chorionated eggs in abdomens. However, high egg loads of the fed females did not alter their behavior in the direction predicted by optimality models. We conclude that oviposition latency was the only variable in which female responses to unsuitable hosts were sufficiently strong to have potential significance for population dynamics. Latency presumably corresponds to dispersing behavior in nature. Such a response, not having been observed in an outbreaking geometrid studied earlier, may reflect a behavioral mechanism capable of stabilizing local population dynamics. The results are discussed in the light of the gradation from capital to income breeding. In herbivorous insects, oviposition latency may serve as an index of overall sensitivity of ovipositing females to adverse environmental conditions.