Impact of Insecticide Applications on Arthropod Predators and Plant Feeders in Cambodian Rice Fields

Abstract

Rice (Oryza sativa) is the staple crop of Cambodia. The heavy use of pesticides has caused significant financial losses to local farmers. This study examined the necessity and economic viability of insecticide use for rice cultivation, and the multiple interactions between the populations of both insect pests and natural enemies in dry-season rice fields. The outcomes of calendar-based insecticide-sprayed and non-sprayed rice fields were compared at three provincial research stations in Cambodia in terms of rice growth, economic returns, damage caused by insect pests, and population dynamics of insect pests and arthropod natural enemies. The results showed that rice fields without insecticide application did not suffer significant damage by insect pests or by diseases and had similar yields to those treated with insecticide application in two provinces. Although the occurrence of caseworm was observed in the third province, this was successfully controlled by an integrated pest management (IPM) treatment without using insecticides. Insufficient densities of natural enemies appeared to correlate with the caseworm outbreak in this location, whereas high densities of natural enemies relative to those of insect pests contributed to control potential pest expansion in the other two provinces. Natural enemy populations were significantly decreased by insecticide applications. Reduced insecticide input in the insecticide-free control and IPM plots resulted in higher net profits than those in insecticide-applied plots, except for plots in the region with a caseworm outbreak (insecticide-free). Overall, this study provides encouraging insight into cost effective and environmentally friendly pest management in Cambodian rice fields.