Genetic diversity of the cotton aphid Aphis gossypii in the unstable environment of a cotton growing area
Résumé
1 Spatial and temporal habitat heterogeneity represented by annual crops is a major factor influencing population dynamics of phytophagous insect pests such as the cotton aphid Aphis gossypii Glover. We studied the effects of instability of the cotton agroecosystem resulting from the temporary availability of the plant resource and the repeated use of insecticides on the genetic variability of the cotton aphids. 2 Samples of A. gossypii were collected in cotton plots, treated or not with insecticides and from vegetable crops (Malvaceae, Cucurbitaceae and Solanaceae) within the cotton growing area of northern Cameroon. The genetic structure of the samples was assessed using eight microsatellite markers. Insecticide resistance was estimated through the detection of two mutations in the ace-1 gene that are associated with insensitivity of acetylcholinesterase to carbamate and organophosphate insecticides. 3 The results obtained show that both host plants and insecticides act in genetic structuring of A. gossypii. Ninety-three percent of aphids collected on cotton were characterized by the same microsatellite multilocus genotype, Burk1, which also displays the insecticide resistant alleles. 4 During the dry season, the cotton crop season after, the genotype Burk1 was principally found on two other malvaceous cultivated plants, rosella and okra, acting as suitable reservoir plants. The ability of the cotton aphid to move among asynchronous suitable habitats in response to changes in resource availability enables the pest to exploit unstable cropping syste