Susceptibility Status of Diamondback Moth, Plutella xylostella (L) to some Insecticides and Role of General Esterases and Acetylcholinesterases in Imparting Resistance

Susceptibility of larvae of diamondback moth, Plutella xylostella collected from Amritsar and Ludhiana in Punjab to fenvalerate, quinalphos and cartap hydrochloride was studied by leaf dip bioassay. Ludhiana population of P. xylostella was 3.1 fold more susceptible than Amritsar population to fenvalerate and 1.6 fold more susceptible than Amritsar population to quinalphos. Quinalphos inhibited 1.6 fold more acetylcholinesterase of Ludhiana population as compared to Amritsar population, and these inhibitions correlated positively with the toxicity. There was negative correlation between general esterase inhibition and toxicity of quinalphos for these two populations. Fenvalerate, a well known sodium channel inhibitor belonging to pyrethroid group, inhibited general esterase more in Ludhiana population than in Amritsar population and these inhibitions correlated with toxicity. Cartap hydrochloride (a synthetic analogue of nereistoxin), an agonist at acetylcholine receptor on post-synapse in nervous system, was 4.5 fold more toxic to Amritsar population than Ludhiana population. Cartap did not affect general esterase or acetylcholinesterase activity in these two populations. In this paper we have shown that estimating inhibition of AChE activity could be a useful tool for quinalphos resistance monitoring in P. xylostella.