Modelling pest population resurgence due to recolonization of fields following an insecticide application.
Abstract
In order to investigate the effect of insect recolonization on the insecticide-induced resurgence of crop pests, a modified Lotka-Volterra predator-prey model was partitioned into two areas, 'sprayed' and 'unsprayed'. The unsprayed area provided a source of insects to recolonize the sprayed area, resulting in a change in pest dynamics in both areas following an insecticide application. Model sensitivity to insecticide selectivity and rates of predation, insect dispersal and pest population increase were examined. Resurgence risk in the sprayed area increased with increasing pest dispersal rate, but decreased with increasing predator dispersal rate. Pest resurgence could also occur in the unsprayed area, especially when prey dispersal rates were low. The extent of resurgence in the unsprayed area could in some circumstances be worse than in the sprayed area itself. The more efficient and longer-lived the predators, the greater the level of pest resurgence in both areas following insecticide use. More selective insecticides, killing the pest, but not the predator, reduced resurgence provided that the average life-span of the predators was reasonably long. Even highly selective insecticides could cause resurgence of the pest in the unsprayed area. When the prey carrying capacity of the unsprayed area was increased relative to that of the sprayed area, resurgent effects in the unsprayed area were reduced, but could still be significant under some circumstances.