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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Insect pests are one of the main detrimental factors for food production systems partially because of the substantial inputs used to control their damage. Pest control typically considers the biology, incidence, and distribution of pest species, and can be improved through understanding the underlying ecology of plant—pest—predator interactions. Integrated pest management programs which include the introduction of insect natural enemies for biological control can supplement the control efforts of pesticide application. However, pesticides can directly affect the survival and performance of beneficial predaceous insects, decreasing their efficacy. Conversely, pesticides may also increase the susceptibility of insects, promoting the predatory performance of their natural enemies. I carried out a series of bioassays in tomato (Solanum lycopersicum L.) to determine the combined effects of a presumed insecticidal botanical extract, karanja oil, on the survival and performance of a pest insect, greenhouse whitefly Trialeurodes vaporariorum (Westwood), and two of its natural enemies, the whitefly parasitic wasp Encarsia formosa (Gahan) and the ladybeetle Delphastus catalinae (Horn). We found a strong negative correlation between increasing concentrations of karanja oil and the survival of whitefly adults and nymphs. The highest concentration (3% v/v%) killed 80% of the whitefly adults and nymphs, whereas the lowest concentration (0.5% v/v%) was lethal to more than 60% of the whiteflies. Karanja oil had a residual negative effect on the immature stages of the whiteflies, and did not interrupt the parasitic performance rate by E. formosa. Karanja oil was lethal to both predators and parasitoids when it was applied directly to them, suggesting that in integrated management programs, natural enemies should be introduced after the application of these botanical derivatives. There was no evidence of plant phytotoxicity on tomato plants at the concentrations of karanja oil that we applied.
Drosophila suzukii is an invasive fruit fly of agricultural concern as it is able to oviposit in ripening and fresh fruit. Olfactory signals in the form of volatile organic compounds (VOCs) may reduce D. suzukii attraction to hosts and decrease survival, but it is unknown how the efficacy of VOCs varies across D. suzukii life stages and how VOCs interact with cultural and biological controls. Peppermint essential oil and fresh peppermint (Mentha x piperita) produce VOCs and recent studies have shown peppermint essential oil to be effective at repelling adult D. suzukii. First, through a series of laboratory bioassays, we evaluated the joint effects of peppermint VOCs on D. suzukii survival and the survival of and parasitism rates by a pupal parasitoid wasp, Pachycrepoideus vindemmiae. We determined whether exposure to peppermint VOCs at the pupal stage reduced adult emergence, and whether this depended on environmental conditions (i.e. soil moisture). Then, we evaluated whether exposure to peppermint VOCs reduced or enhanced parasitism by the pupal parasitoid and whether this depended on the timing of peppermint VOC exposure (i.e. before, during, or after parasitism). Second, we used a intercropping field trial to determine whether intercropping with peppermint plants could reduce D. suzukii infestation in dropped blueberries. We used weekly baited fruit cages to monitor D. suzukii infestation and herbivory by other pests in both a peppermint intercrop and a conventional ryegrass/white clover mix. In our laboratory bioassays, we found that exposure to higher concentrations of peppermint VOCs reduced D. suzukii emergence under moist soil conditions and that this was similar to dry soil with no peppermint exposure. Peppermint VOCs were toxic to adult P. vindemmiae, but developing P. vindemmiae were unaffected by peppermint VOC exposure. In our field experiment, we found low D. suzukii infestations in both intercropping treatments. However we observed increased dropped fruit consumption by slugs, ground beetles and wasps, reducing D. suzukii host sites. Growers may utilize targeted peppermint VOC exposure or intercropping with peppermint to reduce D. suzukii infestation however, this could negatively impact populations of P. vindemmiae dependent on the timing of application.