Indoor residual house spraying using lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane (DDT) was conducted in Zhombe Resettlement area, Zimbabwe. A total of 204/219 (93.1%), 224/260 (86.2%) and 257/325 (79.1%) rooms were sprayed with lambda-cyhalothrin, deltamethrin and DDT wettable powders respectively. Bioassays were conducted on sprayed walls and roofs using 3-5 day old laboratory reared susceptible Anopheles gambiae sensu lato mosquitoes placed in World Health Organization cones.
Bioassays conducted on sprayed walls (1 month), showed that efficacy of lambda-cyhalothrin was the same with DDT but different with deltamethrin and this trend continued in the 2nd month. During the 3rd month, lambda-cyhalothrin killed more mosquitoes than deltamethrin (P=1.931x10-14), DDT killed more mosquitoes than deltamethrin (P=0.0001) and lambda-cyhalothrin killed more mosquitoes than DDT (walls). Efficacy of lambda-cyhalothrin and DDT was the same 4 months post spray (P=0.487), notable differences were seen in lambdacyhalothrin and deltamethrin (P=2.57x10-6), DDT and deltamethrin (P=2.17-10-8). Efficacy of lambda-cyhalothrin and DDT was the same 5 months post spray (P=0.244), major differences were found in lambdacyhalothrin and deltamethrin (P=0.000), DDT and deltamethrin (P=5.18x10-5) and this trend continued in the 6th month. One month after spraying roofs, mortality of mosquitoes due to lambdacyhalothrin/ deltamethrin (P=2.56x10-5), lambda-cyhalothrin/DDT (P=1.2x10-7) and deltamethrin/DDT (P=0.013) were significantly different and this continued in the 2nd month. However, 3 months after spraying, mortality due to lambda-cyhalothrin/deltamethrin (P=1.46x10-6), lambda-cyhalothrin/DDT (P=0.048), and deltamethrin/DDT (P=0.004) were significantly different and this continued in the 4th month. Five months after spraying roofs, mortality due to lambda-cyhalothrin/ deltamethrin (P=0.000) and deltamethrin/DDT (P=6.6x10-7) were significantly different. Six months after spraying, lambdacyhalothrin/ deltamethrin (P=0.34), lambda-cyhalothrin/DDT (P=0.982), and deltamethrin/DDT (P=0.64) were not significantly different. When using exit window traps, no mosquitoes were collected from rooms sprayed with each of the insecticides over a 6-month period. However, 17, 6, 14, 7, 2 and 3 fed An. gambiae sl mosquitoes were collected in the 1st, 2nd, 3rd, 4th, 5th and 6th month respectively from unsprayed rooms and none of them died after 24 h.
spraying, lambdacyhalothrin, deltamethrin, DDT, Anopheles gambiae sensu lato.