Changes In Olfactory And Oviposition Behaviour Induced By Experience Of Momordica Charantia Extract In The Diamondback Moth

Phytophagous insects use plant volatiles in the process of host-finding. Foraging adults are attracted by volatiles emanating from host plants and supposedly repelled by volatiles from non-host plants. As a strategy of behavioral manipulation in IPM, non-host plant chemicals applied on crops play an important role in protecting the target plants, including the effects of repelling insect pests away from the plants, deterring the egg-laying of adults, or killing with toxicity. Therefore, the response of phytophagous insects to the plant secondary metabolites must be considered in developing the strategies for the behavioral control of pests. However, experience-induced habituation or/and preference for plants treated with repellents and deterrents have been shown in phytophagous insects. In this study, we use the diamondback moth Plutella xylostella, its host plant Chinese cabbage, and a non-host plant (Momordica charantia L.) as a model system to examine the effect of experience of non-host plant chemicals on the oviposition behavior of the specialist herbivore. Crude extract of Momordica charantia leaves was collected by SDE (Simultaneous Distillation Extract) and analyzed by GC-MS. Using olfactory response and oviposition preference bioassays, we examined how experience of volatiles chemicals from non-host plants by searching adults affected their subsequent searching and oviposition behavior.(1) Naive females showed no aversion to volatiles emanating from Momordica charantia. When females were given prior experience of Momordica charantia, they increased their choices towards the arm connected to Momordica charantia, but their choices did not differ significantly between Momordica charantia and air.(2) Females in the "no experience" treatment showed significantly aversion responses to plant Momordica charantia in a non-choice test. When Chinese cabbage and Momordica charantia plant were presented together in a choice test to females of the diamondback moth, there were no eggs laid on the Momordica charantia, and the number of eggs laid on Chinese cabbage was significant lower than that on cabbage in the non-choice test. The results showed that Momordica charantia was significantly deterrent to diamondback moth females.When diamondback moths were exposed to plant of Momordica charantia for 24 hours or 48 hours, the females still did not lay eggs on Momordica charantia. However, when the experience time extended to 72 hours, a few eggs were laid on Momordica charantia. But experience of Momordica charantia did not alter the oviposition behavior of diamondback moth females.(3) Responses of experienced females to crude extract of Momordica charantia leaves: In olfactometer tests, naive females showed significant aversion to volatiles emanating from crude extract of Momordica charantia leaves. However, when female moths had an experience of crude extract of Momordica charantia leaves, they expressed habitution and induced preference to the non-host originated repellents, and they were no longer repelled, and increased significantly their acceptance of crude extract.When control plants and treated plants sprayed with the crude extract of Momordica charantia leaves were presented together in choice tests to females of diamondback moth, naive females laid significantly higher number of eggs on the control plants compared to those on the treated plants. When females had an experience of the crude extract of Momordica charantia leaves, they were no longer repelled and instead were attracted by treated plants and laid more eggs on the treated cabbages than on control plants.(4) Crude extract of Momordica charantia leaves were collected by SDE and analyzed by GC-MS. We identified 17 components, including mainly carboxylic acid, alcohol, aldehyde, ketone and ester.To summarize, our study demonstrated Momordica charantia showed significantly deterrence to diamondback moth females, and experience of Momordica charantia did not alter oviposition behavior of diamondback moth females. Naive females showed a significant aversion to volatiles emanating from crude extract of Momordica charantia leaves. Females expressed habituation and induced preference to the non-host originated repellents only with a short prior experience of these substances. These findings have provided another example of insect learning and are useful to manipulation of insect behavior for the purpose of pest management.