Investigation of the effects of ambient humidity on the combined application of Beauveria bassiana (Balsamo) Vuillemin and diatomaceous earth against the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Abstract

Entomopathogenic fungi (EF) and diatomaceous earth (DE) are effective alone or in combination against stored-grain insects. In this study, two Turkish isolates of Beauveria bassiana (Balsamo) Vuillemin and a Turkish DE were tested separately and in combination at three relative humidities (45%, 55%, 65%) and two temperatures (25ºC, 30ºC) to determine their efficacy against adults of the lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). For the bioassays, 50 mL centrifuge tubes containing 40 g of wheat were used. For the controls, wheat alone was used. The EFs and DE were used at 300 ppm (w/w) individually and 300 ppm+300 ppm in combination. Insect mortality was recorded after 7 and 14 days. The application of B. bassiana with DE was equally effective against R. dominica at the three levels of RH used. Therefore, the further testing of combinations of entomopathogenic fungi and diatomaceous earths in grain storages under a range of ambient condition is recommended.