Evaluation of Beauveria bassiana for control of Oebalus pugnax (hemiptera: pentatomidae) in rice

Isolates of Beauveria bassiana (Balsamo) Vuillemin were tested for biological control of rice stink bug, Oebalus pugnax (F.), in the laboratory, in small-plot field experiments compared with conventional insecticides, and in a large-plot experiment to determine the spread and persistence of the fungus. Isolate RSB was found in a naturally- infected O. pugnax in a rice field near Crowley, LA, and isolates LRC28 and LRC21 were obtained for their relatively good growth at high temperatures. The soil-derived isolate LRC28 was more virulent to O. pugnax adults than isolate RSB in a laboratory experiment. The fungal isolates, applied at 5.0-5.7 × 1012 conidia/ha, did not differ from one another in reducing insect numbers or in infecting rice stink bugs in the small-plot experiments, although isolates LRC28 and RSB, but not LRC21, occasionally differed from the control. The overall impact of B. bassiana was moderate on O. pugnax nymphs and minimal on adults in the small-plot experiments. A single application of B. bassiana reduced rice stink bug nymphs on six of nine sampling dates and adults on two of nine sampling dates from 2-10 d after application in the three small-plot experiments, and prevalence of the fungus was higher in the B. bassiana treatment than in controls for nymphs on four dates versus none for adults. A single application of chemical insecticide reduced total rice stink bug numbers more than B. bassiana for at least 7 d in small-plot experiments, whereas a double application was more effective than B. bassiana for 10 d against nymphs. Beauveria bassiana was nearly as effective as a single application of chemical insecticide in suppressing rice stink bug numbers 7-8 d after application. Mixtures of B. bassiana and chemical insecticide provided better control of rice stink bug than a single application of either material alone. Fungal epizootics lasted 17-22 d after application, and a low level of fungus recycling occurred in all of the field experiments. In an experiment to monitor spread, B. bassiana moved rapidly after its application, probably because of host transport. However, disease prevalence did not differ with distance from the treated plot. Disease prevalence was significantly greater in O. pugnax and Lygus spp. than in orthopterans. High temperatures probably were the major factor limiting B. bassiana epizootics in the current research. Thus, B. bassiana has potential for integrated management programs of O. pugnax in rice, because it was moderately effective against nymphs and had an additive effect with insecticides