Abstract
Isolates of Beauveria bassiana (Balsamo) Vuillemin were tested for biological control of rice stink bug, Oebalus pugnax (Fab.), 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. The soil-derived isolate LRC28 was more virulent to O. pugnax adults than the rice stink bug-derived isolate RSB in a laboratory experiment. The fungal isolates did not differ from one another in reducing insect numbers or in infecting rice stink bugs 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 two to 10 days after application, and prevalence of the fungus was higher in the B. bassiana treatment than in controls for nymphs on four dates versus none for adults. Mixtures of B. bassiana and insecticide provided better control of rice stink bug than a single application of either material alone. Fungal epizootics lasted 17-22 days after application. High temperatures probably were the major factor limiting B. bassiana epizootics. Thus, B. bassiana has potential for integrated management programs of O. pugnax in rice, since it was moderately effective against nymphs and had an additive effect with insecticides. Greenhouse experiments were conducted to evaluate the effects of panicle age and grain maturity on quantitative and qualitative damage caused by stink bug infestations on rice. The effects were measured for two infestation levels (one and two bugs per panicle). Insect feeding during anthesis and the early milk stage of grain development caused substantially higher numbers of empty kernels than feeding during later grain development and the control. Average grain weights were lower in infestations during anthesis and milk stage than in infestations during later grain development and the control. Pecky rice was significantly higher during late milk and soft dough stages compared with remaining stages of grain development and the control. Damage was higher in the experiment in which panicles were infested with two bugs.
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