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Evaluation of naturally occurring parasitic Hymenoptera attacking silverleaf whitefly, Bemisia argentifolii in Texas
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Pesticide-free refuge plantings of sunflower, kale and collards were created in association with other plants to provide habitats for the conservation of parasitic Hymenoptera attacking silverleaf whitefly (SWF), Bemisia argentifolii. At least five species of aphelinid parasitoids in the genera Eretmocerus and Encarsia were reared from the whitefly in south Texas. Relative abundance of parasitoid species changes over the season. Encarsia pergandiella was the dominant species and Eretmocerus sp. nr. californicus was the second most abundant species, at times outnumbering E pergandiella; usually at low whitefly densities. Encarsia nigricephala, E sp. nr. strenua and E. quaintancei were also collected. Evaluation of these natural enemies emphasized measurement of whitefly population densities and dispersion, the status of individual whitefly in these populations, changes in parasitoid complexes through time, and exclusion-cage comparisons of their impact on whitefly. Sampling targeted well-developed 4th instar whitefly. Dispersion analysis of E. Pergandiella, E. sp. nr. calijbrnicus and whitefly demonstrated that insect species or plant alone did not have a significant affect on variance-mean ratios. However, the effect of density on variance-mean ratios was significant and at high density, aggregation was significantly higher than at low or medium density levels. These studies indicate there is great potential for indigenous parasitoids to regulate whitefly populations in Texas. Data showed that millions of parasitoids were carried through the winter months on relatively small refuge plantings. Measurements of total parasitism of 4th instar whitefly reached 84% on kale, with corresponding total whitefly mortality greater than 94%. Parasitoid populations readily moved from the refuges onto cotton and maintained whitefly populations that never exeeded 7 whitefly per leaf through the harvest season. Parasitoids showed the ability to respond to whitefly population increases resulting from mass immigration of whitefly into refuges and untreated cotton plots. Parasitoid exclusion cage tests demonstrated a significantly lower whitefly survivorship in the presence of parasitoids than in their absence. Direct parasitism accounted for 65% to 94% of whitefly mortality. There was a cage effect against parasitoids finding the leaves in open cage treatments and there appears to be a significant contribution to whitefly mortality by other natural enemies, particularly predators.
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Moomaw, Charles Philip (1996). Evaluation of naturally occurring parasitic Hymenoptera attacking silverleaf whitefly, Bemisia argentifolii in Texas. Master's thesis, Texas A&M University. Available electronically from
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