Shift in the susceptibility level of Spodoptera litura (Delhi and Guntur populations) to cypermethrin and fenvalerate

The third instar larvae of Spodoptera litura (Fab.) obtained from Guntur district, Andhra Pradesh, were 4 and 5-fold resistant to cypermethrin and fenvalerate, respectively, when compared with the Delhi population. Also, the third instar larvae were less susceptible to fenvalerate than cypermethrin from the same location, i.e., 4.5 and 6.2 times in respect of Delhi and Guntur populations, respectively. A comparison between Delhi population exposed to cypermethrin (LC50, 0.000775) and Guntur population treated with fenvalerate (LC50, 0.019601) revealed that the former was 25.3 times more susceptible. The LC50 values in respect of cypermethrin treated Guntur population (LC50, 0.003155) and fenvalerate treated Delhi population (LC50, 0.003481) were comparable. This suggests that the Delhi population of S. litura in North India appeared to be normal as compared to Guntur population in South India.