摘要：
Simple Summary Habituation to deterrent plant compounds has been found in generalist and specialist insect herbivores. The rate at which plant-feeding insects habituate and at which sensitivity of taste neurons detecting deterrents changes has not been compared among closely related species. The generalist Helicoverpa armigera (Hubner) and the specialist Helicoverpa assulta (Guenee) (Lepidoptera: Noctuidae) differ strongly in degree of host-plant specialism. Both species habituated to the alkaloid strychnine after dietary exposure; however, the specialist H. assulta displayed habituation to strychnine faster (at 48 h) than the generalist H. armigera (at 72 h). Electrophysiological recordings from taste sensilla on mouthparts revealed that a deterrent-sensitive neuron in the medial sensillum styloconicum of both species displayed significantly reduced sensitivity to the deterrent that coincided in time with the onset of habituation. Our findings show that physiological changes in taste neuron sensitivity coincide with habituation to plant compounds that are initially avoided. The two closely related moth species, Helicoverpa armigera and H. assulta differ strongly in their degree of host-plant specialism. In dual-choice leaf disk assays, caterpillars of the two species that had been reared on standard artificial diet were strongly deterred by the plant-derived alkaloid strychnine. However, caterpillars of both species reared on artificial diet containing strychnine from neonate to the 5th instar were insensitive to this compound. Fifth instar caterpillars of H. assulta and 4th or 5th instars of H. armigera not exposed to strychnine before were subjected to strychnine-containing diet for 24 h, 36 h, 48 h, or 72 h. Whereas H. assulta displayed habituation to strychnine after 48 h, it took until 72 h for H. armigera to become habituated. Electrophysiological tests revealed that a deterrent-sensitive neuron in the medial sensillum styloconicum of both species displayed significantly reduced sensitivity to strychnine that correlated with the onset of habituation. We conclude that the specialist H. assulta habituated faster to strychnine than the generalist H. armigera and hypothesis that desensitization of deterrent-sensitive neurons contributed to habituation.
摘要：
The dual-choices tests of behavioral test were used to study the gustatory behavioral responses to caffeine of Helicoverpa armigera larvae and H. assulta larvae. Electrophysiological responses were studied by electrophysiological tip recording. Behavioral experiments showed that caffeine was a feeding deterrent for both larvae,but it showed a stronger feeding deterring effect on the oligophagous H. assulta. The electrophysiological tip-recording results showed that both H. armigera larvae and H. assulta larvae had one caffeine-sensitive feeding deterrent neuron at the medial sensilla,and the electrophysiological pulse response of H. assulta larvae was significantly stronger than that of H. armigera larvae. Therefore,caffeine had a stronger feeding deterring effect on the oligophagous H. assulta than the polyphagous H. armigera. The difference in behavioral effect was closely related to the sensitivity of to caffeine the feeding deterrent neurons at the medial sensilla.
摘要：
<jats:title>Abstract</jats:title><jats:p>Herbivorous insects have been categorized as generalists or specialists depending on the taxonomic relatedness of the plants they use as food or oviposition substrates. The plasticity in host plant selection behavior of species belonging to the two categories received little attention. In the present work, fifth instar caterpillars of the generalist herbivore <jats:italic>Helicoverpa armigera</jats:italic> and its closely related species, the specialist <jats:italic>Helicoverpa assulta</jats:italic>, were fed on common host plants or artificial diet, after which their feeding preference was assessed individually by using dual - and triple- plant choice assays. Results show both the two <jats:italic>Helicoverpa</jats:italic> species have a preference hierarchy for host plants. Compared to the fixed preference hierarchy of the specialist <jats:italic>H</jats:italic>. <jats:italic>assulta</jats:italic>, the generalist <jats:italic>H</jats:italic>. <jats:italic>armigera</jats:italic> exhibited extensive plasticity in feeding preference depending on the host plant experienced during larval development. Whereas the specialist <jats:italic>H</jats:italic>. <jats:italic>assulta</jats:italic> exhibited a rigid preference in both dual and triple-plant choice assays, our findings demonstrate that the generalist <jats:italic>H</jats:italic>. <jats:italic>armigera</jats:italic> expressed stronger preferences in the dual-plant choice assay than in the triple-plant choice assay. Our results provide additional evidence supporting the neural constraints hypothesis which predicts that generalist herbivores make less accurate decisions than specialists when selecting plants.</jats:p>
