Effects of endosulfan, chlorpyrifos and their mixtures onBemisia tabaciof Sudan Gezira

In an attempt to explain the presumed synergism (viz. potentiation) of chlorpyrifos† and endosulfan‡, chlorpyrifos e.c. with endosulfan e.c. at different rates and ratios were tested against Bemisia tabaci (Genn.). Dipped Iubia leaves were used. The additive effect was observed on the LC50 basis, while a potentiation effect was observed at LC50 level. Chlorpyrifos, endosulfan, endosulfan + chlorpyrifos (mix 1, i.e. 10 ppm endosulfan + 14, 10.5, 7 and 3.5 ppm chlorpyrifos), and chlorprifos + endosulfan (mix 2, i.e. 14 ppm chlorpyrifos + 10, 7.5, 5 and 2.5 ppm endosulfan) have shown the following LC50s: 17.37, 9.62, 5.5 and 15.49 ppm, respectively. Following the same order, they showed LC90S of 118.30, 52.67, 13.33 and 23.27 ppm. The slopes of the dosage‐response curves reported were 1.56, 1.76, 3.36 and 7.17, respectively.