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Evaluating parasitoids (Hymenoptera: Aphelinidae) for biological control of Bemisia argentifolii (Homoptera: Aleyrodidae) on poinsettia

by Hoddle, Mark Stephen

Abstract (Summary)
Three aphelinid parasitoids were evaluated for the biological control of silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) on poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) in replicated experimental greenhouses at Cornell University, Ithaca NY. Life-tables for B. argentifolii in the presence and absence of parasitoids were constructed from bi-weekly photographs of whitefly nymphs on poinsettia leaves. Concurrent with photography, weekly population counts of whitefly lifestages on poinsettia plants were made in experimental greenhouses. A release rate of one Encarsia formosa Beltsville strain/plant/week produced 23% parasitism and 96% mortality of photographed nymphs. Releasing three E. formosa Beltsville strain/plant/week caused parasitism to decrease to 12% and whitefly mortality to increase to 99%. Releasing one Eretmocerus sp. nr. californicus (AZ)/plant/week produced 34% parasitism and 88% whitefly mortality. Releasing three E. sp. nr. californicus (AZ)/plant/week caused observed parasitism to decline to 10% and overall mortality of photographed nymphs to increase to 99.1%. The efficacy of these two parasitoids was compared to the commercially available strain of Encarsia formosa Gahan. The commercial strain of E. formosa achieved 23% parasitism and 92% whitefly mortality at a release rate of three females/plant/week. Releasing one female E. formosa/plant/week caused 13% parasitism and 95% whitefly mortality. In a commercial greenhouse, an average weekly release rate of six E. formosa/plant/week resulted in 39% parasitism and 86% mortality. Increasing levels of parasitism and decreasing mortality levels as release rates of commercial E. formosa increase may be due to mutual interference between searching females. Whitefly mortality on greenhouse grown poinsettia in the absence of parasitoids at Cornell University was 19%-25%. To suppress B. argentifolii population growth with inundative parasitoid releases, whitefly net reproductive rates $\rm(R\sb{o})$ have to be less than one. This was achieved when mortality of photographed nymphs exceeded 96%. Discovery and utilization of whitefly nymphs on single leaf poinsettia plants placed within the canopies of commercially grown poinsettia crops indicated that E. sp. nr. californicus (AZ) had a Type I functional response, while E. formosa Beltsville strain exhibited a Type II functional response. E. sp. nr. californicus (AZ) located a greater number of whitefly patches more quickly, and caused higher levels of whitefly mortality than E. formosa Beltsville strain. The observed results may have been affected by the density of whitefly nymphs on non-experimental plants and crop canopy size which differed between greenhouses; both of which were greater in E. formosa Beltsville strain greenhouses.
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Advisor:

School:University of Massachusetts Amherst

School Location:USA - Massachusetts

Source Type:Master's Thesis

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ISBN:

Date of Publication:01/01/1997

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