Herbivore Damage and Prior Egg Deposition on Host Plants Influence the Oviposition of the Generalist Moth Trichoplusia ni (Lepidoptera: Noctuidae)

Abstract

Female insects have the difficult task of locating host plants that maximize the survival and success of their offspring.In this study, the oviposition preferences of the cabbage looper moth, Trichoplusia ni (Hu¨ bner), for soybeanplants, Glycine max (L.), under various treatments?undamaged, mechanically damaged, damaged byT. ni or Spodoptera frugiperda (Smith) larvae or by Bemisia tabaci (Gennadius) adults, egg-free plants, andplants previously oviposited by conspecific or heterospecific females (S. frugiperda)?were investigated usingtwo-choice tests. Additionally, the volatile compounds emitted by the plants under the different treatmentswere identified by gas chromatography?mass spectrometry. Our results showed that females showed no preferencesfor undamaged or mechanically damaged plants. However, they oviposited more often on undamagedplants than on those previously damaged by T. ni, S. frugiperda, or B. tabaci. In contrast, females preferred tooviposit on plants previously oviposited by conspecific and heterospecific females than on egg-free plants.Plants damaged by conspecific or heterospecific larvae emitted methyl salicylate, indole, and octyl butyrate,compounds not released by undamaged or mechanically damaged plants. Whitefly damage induced the releaseof higher quantities of Z(3)-hexenyl acetate, (R)-(þ)-limonene, and (E)-b-ocimene compared to plants damagedby larvae and suppressed the emission of linalool. Egg deposition by conspecific and heterospecific mothsinduced the emission of (R)-(þ)-limonene, octyl butyrate, and geranyl acetone but suppressed the release of linalool.This study showed that a generalist moth species can discriminate between plants of different quality,and suggests that females use volatile compounds as cues during this process.