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Dicyphus hesperus Knight (Hemiptera: Miridae) is an omnivorous natural enemy of greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) that can be used in biological control programs. Omnivorous natural enemies consume both plant and prey food and offer certain advantages and disadvantages to biological control; therefore, understanding these species prior to their use is important. Much is currently known about D. hesperus. However, variation in the quality of plant and/or prey resources for consumers is common in agroecosystems. The impacts of varying within-species resource quality on D. hesperus have not been investigated. The objective of my dissertation was to investigate the effect of varying plant and prey quality on the life history and behaviour of D. hesperus. To approach this question, I used nitrogen (N) fertilizer to manipulate the quality of tomato plants, Solanum lycopersicum L. (Solanales: Solanaceae). Prey reared on high and low N tomato plants were offered in feeding trials to represent natural variation in prey quality. I observed how these factors, independently or simultaneously, affected oviposition preference (Chapter 2); development and survival of D. hesperus nymphs (Chapter 3); olfactory response (Chapter 4); prey preference and consumption rate (Chapter 5); and the activity budget (Chapter 6) of D. hesperus. Based on optimal oviposition theory, optimal foraging theory, and the plant vigor and plant stress hypotheses, I predicted that high N tomato plants, and whitefly prey reared on those plants, would be most preferred. I also predicted that the behaviour of D. hesperus would vary in response to the quality of the resources available. As expected, both factors influenced the life history and behaviour of D. hesperus. For example, high N tomatoes were preferred for oviposition and prey reared on high N plants were preferred for consumption. Foraging behaviour of D. hesperus adults also varied in response to varying levels of plant N when prey from high and low N tomatoes were provided. My results can be used to inform the development of biological control programs using omnivores, and D. hesperus in particular. My research highlights the importance of considering within-species variation in quality when making pest management decisions. |
