Trade-Offs in Rice Pest Management: Enhanced Biological Control and Yield Equivalence Compared with Prophylactic Insecticide Use

Abstract

The study was conducted in four consecutive T. Aman seasons from 2021 to 2024 at the experimental farm of the Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh, to evaluate the impacts of insecticide application on the abundance of harmful and beneficial arthropods in rice ecosystems, comparing conventional farmer practices (prophylactic insecticide application) and researcher-guided practices (need based/rational). Prior to insecticide application, no significant differences were observed in the populations of both harmful insects and beneficial arthropods, confirming a balanced initial baseline. After the 1^st and 2^nd insecticide applications, several pest species- including yellow stem borer (YSB), green leafhopper (GLH), rice leafroller (RLR), white leafhopper (WLH), brown planthopper (BPH), short-horned grasshopper (SHG), and white-backed planthopper (WBPH) showed significantly higher abundance in researcher-guided plots, suggesting that insecticide use initially suppressed insect pests but later (after 3^rd application) rebound. Conversely, all studied natural enemies were consistently and significantly more abundant in researchers-guided plots throughout all sampling periods indicated that, insecticide applications reduce pest populations rapidly and temporarily, but also drastically diminish the abundance of natural enemy, disrupting biological control and fostering potential pest resurgence risk. The higher parasitism rates of BPH (20.20%), RLR (26.78%), and YSB (27.56%) in researcher-practice fields further highlight the contribution of parasitoids and predators to natural pest suppression. Despite reduced chemical insecticide applications, rice yield showed no significant difference between researcher practice (6.21 t ha^-1) and prophylactic insecticide-applied (6.23 t ha^-1) plots. The findings underscore that judicious or minimal insecticide use guided by economic threshold levels can conserve natural enemies, sustain pest regulation, and maintain yield stability.

Bangladesh Rice J.29(1): 53-63, 2025