Insect Predators and Control of Aphis gossypii Comparing to Certain Insecticides under Caged-cotton Plants Conditions

Abstract

Numerous beneficial arthropods prey on aphid populations in cotton fields. Field experiments were conducted at Kafr El-Sheikh Governorate, Egypt in seasons of 2010 and 2011 to examine the impact of naturally occurring insect predators on cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae) comparing to the impact of three insecticides; i.e., diafenthiuron, imidacloprid and thiamethoxam at their recommended rates using caged-plants technique. The toxicity of these insecticides to insect predators was determined likewise. Cotton aphid population on uncaged plants, where insect predators and aphids were allowed to develop undisturbed, declined gradually and consequently showed the lowest population density of aphids per cotton leaf at the last inspection. On the contrary, severe decrease in cotton aphid numbers occurred on caged plants that treated with insecticides and this decrease continued up to 15 days after spray, then increases in aphid numbers happened and significantly indicated the highest aphid population density at the last inspection. Density of aphid populations increased rapidly on caged-untreated plants, where insect predators were excluded and no insecticides were applied and declined only after exceeding the carrying capacity of cotton plants. Diafenthiuron was the most toxic to the insect predators. Imidacloprid and thiamethoxam significantly proved to be the least toxic to insect predators. Further studies are needed to establish the integration effect between selective insecticides and beneficial arthropods to control cotton aphids and other pests.