Abstract: In order to clarify the difference of pyrethroid metabolosim between resistant and susceptible strains, deltamethrin and cypermethrin reporter fluorescent substrates with fluorescent characteristics after hydrolysis were synthesized and used to assay carboxylesterase metabolic activities in different strains of cotton aphid, Aphis gossypii. The results showed that the specific carboxylesterase activities to deltamethrin reporter fluorescent substrate were 10.0 and 3.4 pmol/min·mg in the omethoate-selected resistant and susceptible strains of cotton aphid, respectively, while those to cypermethrin reporter fluorescent substrate were 4.0 and 2.4 pmol/min·mg, respectively. The carboxylesterase activity in the omethoate-selected resistant strain was 2.94- and 1.67- fold compared with that in the susceptible strain when using deltamethrin and cypermethrin reporter fluorescent substrates, respectively. However, the specific carboxylesterase activities to deltamethrin reporter fluorescent substrate were 7.6 and 6.2 pmol/min·mg in the deltamethrin-selected resistant and susceptible strains of cotton aphid, respectively, while those to cypermethrin reporter fluorescent substrate were 9.3 and 5.2 pmol/min·mg, respectively. The carboxylesterase activity in the deltamethrin-selected resistant strain was 1.23- and 1.79-fold compared with that in the susceptible strain when using deltamethrin and cypermethrin reporter fluorescent substrates, respectively. The surrogates for pyrethroids can be used to monitor carboxylesterase hdyrolytic activity of resistant cotton aphids, suggesting that carboxylesterases may be involved in deltamethrin and omethoate resistance in cotton aphids.

Key words: Aphis gossypii, resistance, carboxylesterase, metabolic activity, fluorescent substrate