Development of Insecticide Resistance in Rice Brown Planthopper and Whitebacked Planthopper in Godavari Delta of Andhra Pradesh

Development of insecticide resistance in rice planthoppers viz., brown planthopper, Nilaparvata lugens (Stal) and whitebacked planthopper, Sogatella furcifera (Horvath), was studied during 2004 and 2006. The fieldcollected insects were reared for 3 generations in DRR greenhouse before conducting toxicity tests. Susceptibility of 7–9 day old nymphs was assessed by spraying the commercial formulations of different insecticides at various concentrations on TN1 rice plants upto runoff stage and recording the mortality after 24, 48 and 72 hours of confinement. The LC50 values and resistance ratios (RRs) (LC 50 of resistant population/LC 50 of susceptible population) were worked out. During 2004, in BPH. The resistance ratios for neonicotinoid insecticides viz., imidacloprid, thiamethoxam and clothianidin were 35.1, 10.8, and 4.9 respectively indicating high levels of insecticide resistance. However, BPH remained susceptible to phenyl-pyrazole group insecticides viz., fipronil and ethiprole with RR values of 0.9 and 0.6 respectively. During 2006, BPH in Godavari delta exhibited increased order of resistance to neonicotinoids with RR values of 64.9, 17.9 and 13.2 for imidacloprid, thiamethoxam and clothianidin respectively. BPH in Godavari delta continued to remain susceptible to phenyl pyrazoles like fipronil and ethiprole; organophosphates like acephate and monocrotophos. However, BPH exhibited low to moderate resistance to BPMC, a carbamate. During 2006, whitebacked planthopper from Godavari delta exhibited resistance ratio of 2.7 for clothianidin but remained susceptible to thiamethoxam, acephate, monocrotophos and fipronil recording RR values of around 1.0 or less than1.0. Low to moderate level of resistance was recorded in Godavari WBPH to carbamate insecticide BPMC (RR of 2.7) and insect growth regulator, buprofezin (RR of 2.9).