Entomopathogenic Beauveria bassiana granules to control soil-dwelling stage of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae)

The western flower thrip, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is recognized as a serious pest worldwide, but overuse of chemical pesticides results in environmental pollution and insect resistance. Herein we report the biocontrol of soil-dwelling stages of western flower thrips using entomopathogenic Beauveria bassiana granules. Using a B. bassiana isolate expressing enhanced green fluorescent protein (Bb-egfp), we confirmed that Bb-egfp was highly virulent to the thrips and colonized the soil, which allowed soil-dwelling pupae to come in contact with the colonized fungal mass. In a glasshouse trial, granules of BbERL836 and BbERL1578 isolates were applied to the soil surface of tomatoes growing in pots and female F. occidentalis were released on tomato plants three days after the fungal application. Populations reductions between 75 and 90% were observed in the treatments of BbERL836 and BbERL1578 at 20 and 40 days after application (chemical control: 85% reduction). In the field trial with cucumbers, the two ERL soil treatments showed ca. 90% control efficacy, similar to that of spinetorm, a semi-synthetic insecticide (85% efficacy). This study shows that using entomopathogenic B. bassiana granules to kill soil-dwelling stages of thrips is an effective strategy to manage F. occidentalis populations in tomato and cucumber.