bionomics of aphis gossypii (homoptera: aphididae) and its predators coccinella septempunctata and hippodamia variegata (coleoptera: coccinellidae) in natural conditions

bionomics of aphis gossypii glover and its predators coccinella septempunctata l. and hippodamia variegata goeze were studied in varamin (tehran province) during 11th may to 5th october 2006 on eggplant crop, with the interaction (density dependence) between the aphid and either of the predators determined. the reliable sample size (number of leaves) with a maximum variation of 6.73% was about 56. the index of dispersion, regression models (taylor and iwao), morisita’s index as well as lloyd’s mean crowding to mean were employed to estimate the spatial distribution pattern of the insects. the results indicated that the highest population densities of a. gossypii, c. septempunctata and h. variegata occurred in 8th june (11.62 per leaf), 17th august (0.36 per leaf) and 3rd august (2.11 per leaf), respectively. the index of dispersion, regression models (taylor and iwao), morisita’s index and lloyd’s mean crowding to mean showed aggregated distribution for all species. the linear regression model between prey and predators’ population densities showed a density independent predation by c. septempunctata and h. variegata on a. gossypii. this study indicated that spatial distribution parameters of the cotton aphid and its natural enemies can be employed to outline a sampling program and to estimate the population densities of these insects for use in integrated pest management programs.