Susceptibility of field populations of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and Eretmocerus sp (Hymenoptera: Aphelinidae) to cotton insecticides in Burkina Faso (West Africa).

Research was conducted in 14 cotton fields (3-10 ha) selected in seven localities (two fields per locality) in Burkina Faso, with the objectives of: (1) estimating Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) population abundance, (2) assessing the levels of parasitism by Encarsia spp and Eretmocerus spp (Hymenoptera: Aphelinidae) and (3) estimating the susceptibilities of the pest and of an Eretmocerus sp to the insecticides currently sprayed on cotton. Yellow sticky cards and a leaf-turning technique were used to estimate adult B. tabaci population densities. Yellow sticky cards were also used to estimate the densities of adult Eretmocerus sp and the susceptibilities of B. tabaci to insecticides. Leaf disk techniques were used to estimate B. tabaci red eye nymph populations and parasitism by Encarsia spp and Eretmoceus spp was evaluated using stereo-microscopy. A leaf cage technique was used to estimate the susceptibilities of Eretmocerus sp to insecticides. A mean of 6.5-27.4 adult B. tabaci were trapped per yellow sticky card and 5.5 to > 34.9 were counted per leaf using the leaf turning technique. There were 0.14-13 Eretmocerus sp trapped per yellow sticky card. The levels of parasitism varied between 36 and 87% by the end of the season and parasitism by Eretmocerus sp predominated in most of the fields. The susceptibilities of B. tabaci and Eretmocerus sp varied from field to field and with the insecticide tested.