STRATEGIES OF INSECTICIDE USE TO AVOID RESURGENCE OF NILAPARVATA-LUGENS (HOMOPTERA, DELPHACIDAE) IN TROPICAL RICE - A SIMULATION ANALYSIS

A simulation model of the population dynamics of Nilaparvata lugens (Stal), the brown planthopper, in tropical rice has been used to investigate risk of resurgence due to the application of insecticide. N. lugens resurgence associated with insecticide-induced, natural enemy mortality is simulated by changing the density-dependent survival of N. lugens nymphs after insecticide use. Simulation of the impact on N. lugens populations of different insecticide treatment parameters, notably, time of application, N. lugens: natural enemy kill, residual action, and rate of natural enemy recovery, indicate that resurgence risk is greatest when insecticide is applied about 20 to 25 d after transplanting (DAT). The duration of this risk period, which can sometimes extend from 1 to 40 DAT, is critically dependent on the initial mortality of natural enemy populations and on their subsequent rate of recovery after applications. Implications for practical pest management are discussed.