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UBC Theses and Dissertations

Toxicity across food webs : effect of a botanical extract on tri-trophic interactions in tomato Cabra, César


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.

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