SYNERGISTIC EFFECT OF IMIDACLOPRID AND 2 ENTOMOPATHOGENIC FUNGI ON THE BEHAVIOR AND SURVIVAL OF LARVAE OF DIAPREPES-ABBREVIATUS (COLEOPTERA, CURCULIONIDAE) IN SOIL

The impact of sublethal concentrations of imidacloprid and the entomop athogenic fungi Metarhizium anisopliae (Metschnikoff) Sorokin and Beau verla bassiana (Balsamo) Vuillemin alone or in combination on mobility , mortality, and mycosis of Ist instars of the citrus root weevil, Dia prepes abbreviatus (L.), was evaluated in a series of laboratory bioas says. Initial studies were conducted to determine the effect of soil m oisture and depth oil the rate of larval movement. Movement of 2-d-old larvae in sandy soil was not affected by soil moisture ranging from 2 to 12%, but they did not penetrate soil with < 1% moisture. Movement of 2-d-old larvae was retarded as moisture and soil depth increased. N ewly hatched larvae exhibited poor vertical movement, suggesting that larval age is an important factor to consider in experimentation. In a ll bioassays, soil application of either M. anisopliae or B. bassiana at 5 x 10(3), 5 x 10(4), and 5 x 10(5) conidia per gram of soil as an oil or wettable powder formulation had no effect on the movement of la rvae of D. abbreviatus in soil at different moistures. The addition of imidacloprid to the soil at doses of 5 mu g/g soil or greater signifi cantly impaired larval movement. When the chemical was applied with a fungus, however, larval movement was more severely impaired. Soil trea tment with unformulated conidia of M. anisopliae and B. bassiana as we ttable powder at 5 x 10(3), 5 x 10(4), and 5 x 10(5) caused minimal la rval mortality of D. abbreviatus. In fact. larval mycosis (10.2%) was found only for the B. bassiana oil formulation at 5 x 10(5) conidia pe r gram soil. When sublethal doses of imidacloprid were combined with c onidia of either fungus and applied to the soil, both larval mortality and mycosis increased synergistically. When M. anlsopliae at 5 x 10(5 ) conidia per gram soil were applied alone or in combination with imid acloprid at 25 mu g/g of soil, larval mortality, and mycosis decreased as soil moisture increased from < 1 to 14%.