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Compatibility of Beauveria bassiana with Amblyseius cucumeris to control western flower thrips on cucumber plants

In this research funded by the Horticultural Development Company, a team from Warwick HRI (Dave Chandler, Rob Jacobson, John Fenlon, Karen Russell) investigated Beauveria bassiana as a compatible biopesticide with the predatory mite Amblyseius cucumeris [= Neoseiulus cucumeris] for control of western flower thrips, Frankliniella occidentalis. Western flower thrips is the most damaging pest of protected cucumbers in the UK. Infestations can cause severe crop damage, and management with chemicals is made difficult by widespread pesticide resistance. Hence, biological control measures are required for this pest that are reliable and compatible with other components in the IPM programme for the crop.

Earlier research by Rob Jacobson had led to a method of suppressing the establishment of F. occidentalis on cucumber crops by early release of the predatory mite, Amblyseius cucumeris [Neoseiulus cucumeris]. This method is now used as standard practice in protected crops. However, there are occasions when control with A. cucumeris breaks down. This is usually due to the application of fungicides that are harmful to A. cucumeris, or the sudden immigration from other crops of large numbers of F. occidentalis.

We studied the effects of the entomopathogenic fungus Beauveria bassiana on populations of western flower thrips, and its compatibility with Amblyseius cucumeris in laboratory and glasshouse experiments. Two proprietary B. bassiana-based mycopesticides were used. Two high volume sprays of the fungus, applied with a six day interval to glasshouse-grown cucumber crops, reduced numbers of immature F. occidentalis by 75% compared to an untreated control during the three weeks following the first application. Glasshouse populations of F. occidentalis were also reduced by 65 – 87% with three consecutive high volume sprays or low volume mist applications, applied at six day intervals. Prophylactic release of A. cucumeris in glasshouse-grown cucumbers prevented population increases of F. occidentalis. The fungus had no detrimental effect on A. cucumeris when sprayed onto excised cucumber leaves in a laboratory bioassay, or when sprayed onto glasshouse-grown cucumbers. There was no evidence that control of F. occidentalis was impaired by application of the fungus onto plants already treated with A. cucumeris.

The study suggests that a mycopesticide could be used as a second line of defence to support preventative pest management with A. cucumeris. This strategy provides a way forward for biological control in protected crops.

Selected reference:

JACOBSON, R. J., CHANDLER, D., FENLON, J. & RUSSELL, K. M. (2001). Compatibility of Beauveria bassiana (Balsamo) Vuillemin with Amblyseius cucumeris Oudemans (Acarina: Phytoseiidae) to control Frankliniella occidentalis Pergande (Thysanoptera:Thripidae) on cucumber plants. Biocontrol Science and Technology, 11, 381 - 400.

Western flower thrips infected with Beauveria

Western flower thrips infected with Beauveria