INTERACTIONS BETWEEN BIOLOGICAL-CONTROL EFFORTS AND INSECTICIDE APPLICATIONS IN TROPICAL RICE AGROECOSYSTEMS - THE POTENTIAL ROLE OF INTRAGUILD PREDATION

Integrated pest management attempts to combine cultural, chemical, and biological approaches to bring about pest reductions and improve crop yields. In Asian wet rice agriculture, as in many crop systems, there is a real question as to how compatible chemical control methods are with other pest control approaches, Working in an irrigated rice paddy on Java, Indonesia, we crossed a natural enemy treatment (addition of wolf spiders, Lycosa pseudoannulata Boesenberg et Strand) with an ins ecticide treatment (monocrotophos) in a balanced, replicated, two-way factorial design to explicitly examine the potential interactions betw een chemical and biological control methods. Although adding either wo lf spiders or insecticide to field plots significantly reduced abundan ce of pests (sucking homopterans), combining the two treatments togeth er generated a significant, season-long interaction effect such that p est densities did not decrease, In other words, pest densities in plot s receiving both spiders and insecticide were statistically comparable to those in plots receiving neither pest control method. Furthermore, we found additive effects of wolf spiders and insecticide on other ge neralist predators, and from those data we hypothesize that intraguild predation and ensuing indirect effects may be responsible for the int eraction effect on pest density. Our results indicate that, far from b eing complementary and compatible approaches to pest reduction, combin ing treatments of natural enemy addition and insecticide application m ay be quite counterproductive. (C) 1998 Academic Press.