The residual effect of lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane in Zhombe, Kwekwe district, Zimbabwe

Abstract

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 <em>Anopheles gambiae sensu lato </em>mosquitoes placed in World Health Organization cones. <br />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 2<sup>nd</sup> month. During the 3rd month, lambda-cyhalothrin killed more mosquitoes than deltamethrin (P=1.931x10<sup>-14</sup>), 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<sup>-6</sup>), DDT and deltamethrin (P=2.17-10<sup>-8</sup>). 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<sup>-5</sup>) and this trend continued in the 6<sup>th</sup> month. One month after spraying roofs, mortality of mosquitoes due to lambdacyhalothrin/ deltamethrin (P=2.56x10<sup>-5</sup>), lambda-cyhalothrin/DDT (P=1.2x10<sup>-7</sup>) and deltamethrin/DDT (P=0.013) were significantly different and this continued in the 2<sup>nd</sup> month. However, 3 months after spraying, mortality due to lambda-cyhalothrin/deltamethrin (P=1.46x10<sup>-6</sup>), lambda-cyhalothrin/DDT (P=0.048), and deltamethrin/DDT (P=0.004) were significantly different and this continued in the 4<sup>th</sup> month. Five months after spraying roofs, mortality due to lambda-cyhalothrin/ deltamethrin (P=0.000) and deltamethrin/DDT (P=6.6x10<sup>-7</sup>) 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 <em>An. gambiae sl </em>mosquitoes were collected in the 1<sup>st</sup>, 2<sup>nd</sup>, 3<sup>rd</sup>, 4<sup>th</sup>, 5<sup>th</sup> and 6<sup>th</sup> month respectively from unsprayed rooms and none of them died after 24 h.