Enzymatic susceptibility evaluation of different populations of melon aphid Aphis gossypii (Hemiptera: Aphididae) to two insecticides: spirotetramat and flonicamid

Aphis gossypii Glover (Hemiptera: Aphididae) is one of the most important pests of cucumber and its resistance to insecticides has caused many problems in controlling measures. Collecting fundamental data by using bioassay and biochemical tests is essential for pest resistance management. In this study, the susceptibility of the pest to the insecticides; spirotetramat and flonicamid was investigated for two populations collected from Karaj (Alborz Province) and Birjand (South Khorasan Province), Iran. Bioassay tests were conducted by leaf disk immersion method. Mortality was recorded after 72 hours. The data analysis was performed by Polo-Plus software. Results showed that in Karaj and Birjand populations, the LC50 values for spirotetramat were 52.81 and 33.35 mg. a.i /L, respectively, and for flonicamid were 6.78 and 3.7 mg. a.i/L, respectively. The LC50 Ratio values for spirotetramat and flonicamid were 1.633 and 1.829 for those populations, respectively which were significantly different. Also results of biochemical tests showed higher resistance in Karaj population. Different enzymes involved in resistance include carboxyl esterase (evaluated by α-naphthyl acetate and ß-naphthyl acetate substrate), glutathione S-transferase and monooxygenase. The activity ratios of above-mentioned enzymes in Karaj population were 1.39، 1.29، 1.51 and 1.06 times higher than those in Birjand population, respectively. The enzymatic results were parallel with the results obtained from the bioassay tests. Therefore, it seems that all three enzymatic systems are involved in detoxifying of the tested compounds.