A Study Of Oviposition Selection Behaviors For Ambrosia Artemisiifolia And Xanthium Sibiricum In Ophraella Communa (Coleoptera:Chrysomelidae)

The leaf beetle Ophraella communa is an effective biological control agent of the alien invasive ragweed, Ambrosia artemisiifolia in China. That it feeds the non-target Xanthium sibiricum in Japan is hypothesized as the evidence of host shift in the invaded area. This thesis study was designed to evaluate host specificity of oviposition of adults when their larvae accomplished development on either A. artemisiifolia or X. sibiricum, with the goal of determine if this leaf beetle has shifted its host from the target to the non-target plants. Results and conclusions were obtained from this study as follows:1. Oviposition behavior on test plants of adults whose larvae developed on different plantsOviposition plant selection is one of important traits for evaluating host specificity in herbivorous insects. To assess effects of larval feeding and oviposition plants on oviposition selection in the nonnative leafbeetle Ophraella communa,, a repeated measure design was used in trials in outdoor slat house to investigate oviposition selection of the adults that fed on either the common ragweed Ambrosia artemisiifolia or the non-target cocklebur Xanthium sibiricum during their larval stage. In the non-choice trial, analyses of number of eggs deposited showed that there was no significant difference between larval feeding plants, but there was between oviposition plants. The number of eggs deposited was higher on the cocklebur than on the common ragweed tested for oviposition, laying24.39or25.12eggs on the former and8.94or21.90eggs on the later by adults that fed on A. artemisiifolia or X. sibiricum, respectively. The analysis of egg size (measured as volume) showed that there was no significant difference between testing oviposition plants, but there was between larval feeding plants where adults laid larger eggs when their larvae fed on the common ragweed than on the cocklebur. There were no significant differences in egg hatching rate between feeding and ovipsoition plant treatments, which ranged from60%and70%. 2. Oviposition choice of adults whose larvae developed on different plantsChoice-trials were made to examine oviposition preferences between the target and non-target plants of adults that completed larval development on these plants respectively. The results showed that O. communa adults from both A. artemisüfolia and X. sibiricum showed a strong preference to laying eggs on the former plant The proportion choices for A. artemisiifolia was more than77.%. But there was no significant difference in number of eggs between the plants on which the larvae fulfilled their development. The study did not find significant differences in number of eggs and egg size between larval feeding plants and between oviposition test plants. Results of choice testing suggested that O. communa had an oviposition preference on A. artemisiifolia.3. Survival of offspring on test plants of adults whose larvae developed on different plantsThe experiments were made to examine survival on A. artemisiifolia and X. sibiricum of offspring produced by adults whose larvae completed their development on these plants. Results from the analysis using Cox proportion hazard model showed that mortality risk (measured by instant probability of death) on A. artemisüfolia of the offspring produced by adults that came from A. artemisüfolia was significantly lower than that on X. sibiricum. Mortality risk on A. artemisüfolia of the offspring produced by adults that came from X. sibiricum was also significantly lower than that on X. sibiricum. Mortality risk (measured by instant probability of death) on X. sibiricum of the offspring produced by adults that came from X sibiricum was significantly lower than that on A. artemisiifolia, but there was no significant difference on A. artemisüfolia between them. Body weights of pupae on A. artemisüfolia from A. artemisüfolia and X. sibiricum were both significantly heavier than those on X. sibiricum. There was no significant difference between body weights of pupae on the same plant from different plants.