Development of Resistance to Carbofuran, Phosphamidon and Neem oil in Rice BPH, Nilaparvata lugens Populations in Tamii Nadu, India

Dose response bioassays were conducted using fourth - fifth instar brown planthopper (BPH) nymphs reared on TN1 rice seedlings BPH nymphs were topically dosed with insecticides or neem oil in an aliquot of 0.2 mL with the median lethal doses (LD₅₀) derived for carbofuran (0.0012 μg), phosphamidon (0.016 μg) and neem oil (9.14 μg) used for selection. Selection for the development of resistance was done by topical application of LD₅₀’s through fourth, fifth, sixth, seventh, eighth and ninth generations. The resistance ratios were 4.0, 2.3 and 1.4 for carbofuran and 2.2, 1.7 and 1.3 for phosphamidon based on LD₅₀, LD₉₀, and LD₉₉ respectively. The LD₅₀ and LD₉₀ of neem oil did not vary much among the nine generations tested indicating that there is no development of resistance with neem oil. The rate of resistance development was very low, which is evident from the low R and high ‘G’ values.