Sequential Sampling Plan for Rice Planthoppers with Incorporation of Predator Effect

Abstract

Spatial distribution of rice planthoppers, Nilaparvata lugens (Stal) and Sogatella furcifera (Horvath) together, and their predators, spiders and mirid bugs was studied on Pusa 1121 rice during rainy season 2010 through Taylor's power law and Iwao's mean crowding regression. Planthoppers as well as their predators followed aggregated distribution in the field. Sequential sampling plans based on Taylor's distribution parameters (a = 0.398, b = 1.614) and economic injury level (10 hoppers/hill) were formulated for rice planthoppers with and without consideration to predation by spiders and mirid bugs. During pre-flowering, sequential plans suggested need for control when two rice hills harboured cumulative planthopper population of 36 hoppers with predators and 27 hoppers without predators. Likewise, during post-flowering phase, control was required if two rice hills had cumulative population of 51 hoppers with predators compared to 27 hoppers without predators. Sequential sampling plans with predator effect thus suggested need for management measures at higher planthopper population. This would be helpful in avoiding unwarranted pesticide application thereby ensuring natural enemy conservation and favourable benefit- cost to farmers.