Abstract

Two populations of Aphis gossypii were collected from cotton and melon crops treated with insecticides to control this aphid species. The susceptibility of both aphid populations to pymetrozine, Pirimicarb, Oxydemeton-methyl and Imidacloprid was evaluated using leaf deep bioassays in Laboratory which were commonly used to control this aphid on both crops. Results showed that LC₅₀ values of these insecticides against clones of cotton aphid were 452, 1427, 1810 and 209 ppm, respectively. LC₅₀ values of the above mentioned pesticides against clones of melon aphid were 625, 688, 523 and 125 ppm, respectively. Lc₅₀ data showed that aphids reared on melon was 2.07, 1.6 and 3.4 times more susceptible than cotton aphids to Pirimicarb, Imidaclopride and Oxydemeton-methyl and 1.4 times more resistant to Pymetrozine, respectively. In conclusion, it has been shown that clones of cotton aphid is on average 3.4-fold less susceptible to Oxydemeton- methyl, 2-fold less susceptible to pirimicarb, 1.6-fold less susceptible to Imidacloprid and nearly 0.7-fold more susceptible to pymetrozine than clones of melon aphid. There was little difference in susceptibility to pymetrozine between the two populations. It is also suggested that continuous resistance monitoring should be conducted on a regional scale to identify the efficiency of compounds which are applied against this insect species.

Key words: Aphis gossypii, cotton, melon, insecticide resistance.