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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Manipulating Spray-Application Parameters on Efficacy of the Entomopathogenic Fungus Beauveria Bassiana Against Western Flower Thrips, Frankliniella Occidentalis, Infesting Greenhouse Impatiens Crops

Authors
item Ugine, Todd - CORNELL UNIVERSITY
item Wraight, Stephen
item Sanderson, John - CORNELL UNIVERSITY

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2006
Publication Date: March 5, 2007
Citation: Ugine, T.A., Wraight, S.P., Sanderson, J.P. 2007. Effects of manipulating spray-application parameters on efficacy of the entomopathogenic fungus beauveria bassiana against western flower thrips, frankliniella occidentalis, infesting greenhouse impatiens crops. Biocontrol Science and Technology. 17:193-219.

Interpretive Summary: Western flower thrips are minute insects that inhabit cryptic microhabitats on plants, especially in flowers. Nymphs develop rapidly, with short periods between molts; adults begin producing eggs soon after emergence and have a high rate of reproduction. These characteristics make thrips exceedingly difficult to control. Growers generally rely on chemical insecticides, yet there is interest in developing safer, sustainable alternatives. Microbial biocontrol with insect pathogenic fungi is one alternative; however, efficacy of these agents is limited by slow action, specific environmental requirements, and other factors. To realize the full potential of these agents, research is needed to identify optimal methods and strategies for their use. In this study we manipulated various spray parameters, including application rate, volume, and frequency, and spray-program timing, in an attempt to maximize efficacy of a wettable powder formulation of Beauveria bassiana. Numbers of fungal spores inoculated onto thrips increased with increasing spray frequency and volume. Numbers, however, were unexpectedly not directly correlated with application rate, suggesting that thrips avoided concentrated spray residues. Significant control was achieved only when 3–4 sprays were applied at the highest label rate in a high spray volume at 5-day intervals. Applications against thrips in young, preflowering impatiens crops were not consistently more effective than applications in older crops. The most effective treatment programs reduced pest populations by 30–40% compared to untreated controls; this slowed, but did not stop, the growth of pest populations. Results indicate that use of fungi for thrips management will require integration with other control agents.

Technical Abstract: The effects of various spray application parameters on the efficacy of a clay-based wettable powder formulation of Beauveria bassiana strain GHA conidia against western flower thrips Frankliniella occidentalis were evaluated in a series of greenhouse tests. Impatiens crops infested with thrips were subjected to various combinations of treatments at rates of 5 x 1013 – 2.0 x 1014 conidia, volumes of 935–3740 L aqueous carrier/ha, and application intervals of 3–7 days. Efficacy was also evaluated for spray programs initiated before vs. after the onset of flowering. Samples of pollen-bearing impatiens flowers were taken twice weekly to estimate thrips population densities, and adult female and second-instar nymphs were collected 24 h post-inoculation and examined microscopically to determine actual doses of conidia acquired per insect. Numbers of conidia inoculated onto thrips increased with increasing spray frequency and volume. The acquired dose was unexpectedly not directly correlated with application rate when volume was held constant, suggesting that thrips avoided concentrated spray residues. Statistically significant control was achieved only when 3–4 sprays were applied at the highest label rate in the highest volume at 5-day intervals. Applications against thrips in young, preflowering impatiens crops were not consistently more effective than applications in older crops. The most effective spray programs reduced pest populations by 30–40% compared to untreated controls; this slowed, but did not stop, the growth of pest populations.Results indicate that use of fungi for thrips management will require integration with other control agents.

Last Modified: 10/1/2014
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