| The biecology of the white rice stem borer (WSB), Scirpophaga innotata Walker (Lepidoptera: Pyralidae), was studied in West Java, Indonesia, with the overall objective of elucidating the factors responsible for a recent outbreak of this pest. Specific objectives included investigations of WSB diapause, comparative effects of two rice varieties (IR 64 and Cisadane) on WSB performance, and effects of insecticides (carbofuran) and egg parasitoids on WSB population dynamics.;WSB survives the off-rice season as a diapausing larva. Photoperiod was documented as the primary cue for diapause induction, with plant factors (rice growth stage and variety) possibly having a secondary role. WSB apparently exhibits a long-day or Type-I photoperiodic response, with a critical photoperiod of about 11 hours 45 minutes. Moisture is required for diapause termination.;For all demographic statistics considered, IR 64 proved to be a better host plant than Cisadane. The intrinsic rate of increase for WSB reared on IR 64 was about twice that on Cisadane, the mean generation time was about five days shorter, and the doubling time was about one half. Simulations using a simple Leslie matrix model suggested that under undisturbed conditions, an initial moth density of 200 per hectare is capable of causing economic damage on IR 64, whereas an initial density an order of magnitude higher is required to produce the same result on Cisadane plants.;Prophylactic applications of the insecticide carbofuran in seedbeds and on transplanted crops did not provide good control of WSB populations, but instead tended to disturb parasitoid populations. Computer simulation experiments, using a model that incorporates WSB and egg parasitoid dynamics on IR 64 plants, indicated that parasitoids are able to prevent WSB populations from reaching damaging levels in the absence of insecticides. |
