jear2012 Abstract Indoor residual house spraying using lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane (DDT) was con- ducted 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 effica- cy 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=1.931¥10-14), 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 lambda- cyhalothrin and deltamethrin (P=2.57¥10-6), 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 lambda- cyhalothrin and deltamethrin (P=0.000), DDT and deltamethrin (P=5.18¥10-5) and this trend continued in the 6th month. One month after spraying roofs, mortality of mosquitoes due to lambda- cyhalothrin/deltamethrin (P=2.56¥10-5), lambda-cyhalothrin/DDT (P=1.2¥10-7) and deltamethrin/DDT (P=0.013) were significantly differ- ent and this continued in the 2nd month. However, 3 months after spray- ing, mortality due to lambda-cyhalothrin/deltamethrin (P=1.46¥10-6), 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=6.6¥10-7) were sig- nificantly different. Six months after spraying, lambda- cyhalothrin/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. Introduction The use of residual insecticides for indoor residual house spraying (IRS) remains an essential component of malaria control in many parts of the world, including Zimbabwe (Eilsele, et al., 2010). Residual insecti- cides have life spans of 3-6 months for pyrethroids (Raghavendra et al., 2011) and 8 months to 2 years for organo-chlorines (Taylor et al., 1981). IRS targets mosquitoes that are endophillic (indoor resting) that will eventually pick up a lethal dose before they die. In a study conducted in Kenya, IRS reduced mosquito vector density and disease incidence for a period of 6 months (Zhou et al., 2010). Molineaux & Gramiccia (1980) attributed vector exophily to the failure to interrupt malaria transmission following IRS with the insecticide propoxur in Nigeria. Sharp et al. (2007) observed that the number of Anopheles gambiae sensu stricto mos- quitoes was reduced from 25.5 to 1.9 per trap per 100 nights after spray- ing with a pyrethroid. World Health Organization (WHO, 2006) set the criteria for knock down as ≥95% and 24 h mortality as ≥80% and a spray- ing coverage of >80% is required in order to interrupt transmission. The epidemiology and history of malaria control in Zimbabwe is well Correspondence: Nzira Lukwa, National Institute of Health Research, P.O. Box CY573, Causeway, Harare, Zimbabwe. Tel: +263.4.797052 - Fax: +263.4.253979. E-mail: nziraa33@yahoo.co.uk Key words: spraying, lambdacyhalothrin, deltamethrin, DDT, Anopheles gambiae sensu lato. Contributions: NL, SLM, research concept and design, data collection tools, data analysis and interpretation, manuscript first draft, revision and final approval; AM, PM, improving methodology, data collection tools, data analy- sis, manuscript revision and final approval. Acknowledgements: the authors would like to thank Mrs M. Gidi, Mr F. Chinyanya, Mr Mupindu and Mrs Rwizi for their support. This study could not have been possible without authority from Dr Chimusoro and Mrs Vimbayi Chikwavaire. Several people assisted in many ways and are duly acknowledged. Received for publication: 5 June 2012. Revision received: 25 August 2012. Accepted for publication: 28 August 2012. ©Copyright N. Lukwa et al., 2012 Licensee PAGEPress, Italy Journal of Entomological and Acarological Research 2012; 44:e10 doi:10.4081/jear.2012.e10 This article is distributed under the terms of the Creative Commons Attribution Noncommercial License (by-nc 3.0) which permits any noncom- mercial use, distribution, and reproduction in any medium, provided the orig- inal author(s) and source are credited. The residual effect of lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane in Zhombe, Kwekwe district, Zimbabwe N. Lukwa,1 A. Makuwaza,1 S.L. Mutambu,1 P. Munosiyei2 1National Institute of Health Research, Causeway, Harare; 2Bindura University of Science Education, Zimbabwe [page 46] [Journal of Entomological and Acarological Research 2012; 44:e10] Journal of Entomological and Acarological Research 2012; volume 44:e10 No n- co mm er cia l u se on ly documented by Taylor & Mutambu (1986). Malaria vector control start- ed in the 1940s and has witnessed the coming and going of such insec- ticides as dieldrin and benzene hexachloride and the introduction of synthetic pyrethroids such as deltamethrin, alpha-cypermethrin, and lambda-cyhalothrin. IRS remains an essential component of the National Malaria Control Programme (NMCP) in Zimbabwe. Information from previous work indicates that the malaria vectors in Zimbabwe are still susceptible to dichlorodiphenyltrichloroethane (DDT) and pyrethroids (Manokore et al., 2000) although Munhenga et al. (2008) documented resistance to permethrin and DDT of mosqui- toes collected from one locality in Gwave, Zimbabwe. The residual effect of DDT, lambda-cyhalothrin and deltamethrin was monitored in Zhombe resettlement area, Zimbabwe. Material and methods Study area Zhombe is one of the malarious areas in Kwekwe district that is not sprayed by the NMCP during its annual spraying cycle. Malaria spray- ing by the NMCP focuses on the highly burdened districts. Insecticides DDT 75WP is a wettable powder containing 75% dichloro-diphenyl- trichloro-ethylene, Insectokill 10WP contains 10% lambda-cyhalothrin wettable powder and Deltaguard 5WP contains 5% deltamethrin wet- table powder. Deltamethrin (moderately toxic) has an acute toxicity of lethal dose for 50% effect (LD50) oral, rat. >5000 mg/kg and LD50 dermal, rat. >2000 mg/kg. Lambda-cyhalothrin (moderately toxic) has an acute toxicity of LD50 oral, rat. 144 mg/kg and LD50 dermal, rat. 696 mg/kg. DDT (moderately to slightly toxic) has an acute toxicity of LD50 oral, rat. 113-800 mg/kg and LD50 dermal, rat. 2500-3000 mg/kg Spraying was conducted using an Xpert 8L Hudson sprayer (H.D. Hudson Manufacturing Company, Chicago, IL, USA), pressurised to 55 psi (pounds per square inch). One hut in Zimbabwe constitutes one room only. A total of 204/219 (93.1%) rooms were sprayed with lambda- cyhalothrin at 30 mg/m2, 224/260 (86.2%) rooms were sprayed with deltamethrin at 25 mg/m2, 257/325 (79.1%) rooms were sprayed with DDT at 2 mg/m2 and 205 rooms served as the control. All insecticides were sprayed in March 2010. Mosquitoes Anopheles gambiae sensu lato mosquito larvae were collected from the study sites through larval scooping. The larvae were placed in lar- val bowls (rearing dishes) in a simulated field insectary and reared to adult stage by the provision of fish food. The resulting female adults were given 10% sugar water. The mosquito colony is susceptible to 4% DDT, 0.05% deltamethrin, 0.05% lambda-cyhalothrin, 0.5% etofenprox, 0.15% cyfluthrin and 0.75% permethrin. Residual effect Bioassays were conducted on randomly selected rooms (Table 1) that were sprayed with DDT, lambda-cyhalothrin or deltamethrin in accor- dance with WHO guidelines (2006). Three WHO cones (8.5 cm in diam- eter at the base and 5.5 cm high) were fastened on different positions on the wall and other 3 on the roof. Ten to fifteen An. gambiae sl mos- quitoes were aspirated and placed in each WHO cone and exposed for 30 min. Mosquitoes were retrieved using an aspirator, placed in a hold- ing cup before recording knock down rate. These mosquitoes were pro- vided with 10% sugar solution in a 50 mL bottle that contained a wick and this was done over a period of 6 months. Mortality was scored after 24 h. By adding up all mosquitoes that died in each cone for each sur- face and dividing by the number of cones, the mean mortality per month for each insecticide was calculated. Effect of insecticides on mosquito behaviour This was done monthly using Exit Window Traps (EWT) mounted at 1 window opening at each homestead at 5 p.m. Five rooms for each insec- ticide were used every month for 6 months and this included 5 unsprayed rooms that served as controls. All the other windows and openings were then closed. Mosquito collection was done using an aspirator and placing mosquitoes in a holding cup by 10 a.m. the following day. Data analysis The data analysis was performed with the ANOVA test (analysis of variance) using the 95% confidence limit. Mortality of mosquitoes at each time pont was analyzed for the 3 insectides. Results Results for bioassays conducted on sprayed walls are shown in Table 2. No mortality occurred in the 2 control rooms that were used per month, with a total of 12 control rooms over the 6-month period. The mortality for mosquitoes exposed to walls sprayed with lambda-cyhalothrin (1 month) was the same with DDT but significantly different with deltamethrin. Two months after spraying, mortality for mosquitoes due to lambda- cyhalothrin was significantly different with deltamethrin (P=0.003) and DDT (P=0.03). During the same period, DDT and deltamethrin were sig- nificantly different (P=1.31¥10-5). During the 3rd month, lambda- [Journal of Entomological and Acarological Research 2012; 44:e10] [page 47] Article Table 1. Number of rooms used for bioassays. Months post Lambda-cyhalothrin Deltamethrin DDT Control spraying Rooms where Rooms where Rooms where Rooms where Rooms where Rooms where Rooms walls were used roofs were used walls were used roofs were used walls were used roofs were used used 1 4 4 6 5 6 5 2 2 7 8 6 4 6 5 2 3 7 7 8 6 4 4 2 4 4 6 4 4 4 4 2 5 5 5 4 4 6 9 2 6 7 9 6 6 4 1 2 DDT, dichlorodiphenyltrichloroethane. No n- co mm er cia l u se on ly [page 48] [Journal of Entomological and Acarological Research 2012; 44:e10] cyhalothrin killed more mosquitoes than deltamethrin (P=1.931¥10-14), DDT killed more mosquitoes than deltamethrin (P=0.0001) and lambda- cyhalothrin killed more mosquitoes than DDT (all results were signifi- cantly different). Efficacy of lambda-cyhalothrin and DDT was the same 4 months post spray (P=0.487), notable differences were seen in lambda- cyhalothrin and deltamethrin (P=2.57¥10-6), 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 lambda- cyhalothrin and deltamethrin (P=0.000), DDT and deltamethrin (P=5.18¥10-5). Efficacy of lambda-cyhalothrin and DDT was the same 6 months post spray (P=0.427), major differences were found in lambda- cyhalothrin and deltamethrin (P=3.7¥10-7), DDT and deltamethrin (P=1.58¥10-9). No mortality was observed with the control mosquitoes over the 6-month period. Results for bioassays conducted on sprayed roofs are shown in Table 3. One month after spraying, the mortality of mosquitoes due to lamb- da-cyhalothrin/deltamethrin (P=2.56¥10-5), lambda-cyhalothrin/DDT (P=1.2¥10-7) and deltamethrin/DDT (P=0.013) were significantly dif- ferent. Results for 2 months after spraying, mortality due to lambda- cyhalothrin/deltamethrin (P=3.65¥10-11), lambda-cyhalothrin/DDT (P=9.18¥10-12), and deltamethrin/DDT (P=2.26¥10-5) were significant- ly different. Three months after spraying, mortality due to lambda- cyhalothrin/deltamethrin (P=1.46¥10-6), lambda-cyhalothrin/DDT (P=0.048), and deltamethrin/DDT (P=0.004) were significantly differ- ent. Four months after spraying, mortality due to lambda-cyhalothrin/ deltamethrin (P=1.46¥10-6), lambda-cyhalothrin/DDT (P=0.048), and deltamethrin/DDT (P=0.004) were significantly different. Five months after spraying, mortality due to lambda-cyhalothrin/deltamethrin (P=0.000) and deltamethrin/DDT (P=6.6¥10-7) were significantly dif- ferent apart from lambda-cyhalothrin/DDT (P=0.811). Six months after spraying, lambda-cyhalothrin/deltamethrin (P=0.34), lambda- cyhalothrin/ DDT (P=0.982), and deltamethrin/DDT (P=0.64) were not significantly different. No mortality was observed with the control mos- quitoes over the 6-month period. Effect of insecticides on mosquito behaviour After installing one exit window trap per room for a total of 5 rooms per treatment per month, no mosquitoes were collected from rooms sprayed with 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. Discussion and conclusions Spraying coverage was above 80% as required by WHO (2006) in lambda-cyhalothrin and deltamethrin sprayed villages although slightly low in DDT sprayed villages. We did not carry out a study on level of product acceptability in the study villages and therefore cannot explain these observed differences. The number of rooms used for bioassays sometimes differed in some months due to either availability of mosquitoes or presence of the head of a household to give consent. During the first month on sprayed walls, deltamethrin was not as effective as either lambda-cyhalothrin of DDT but this trend was totally different on sprayed roofs over the same peri- od. In the second and third month, the efficacy of these 3 insecticides was totally different on the walls and roofs. During the 4th month, effi- cacy of lambda-cyhalothrin and DDT on walls was the same but differ- ent with deltamethrin but all roofs were totally different over the same period. In the 5th month, efficacy of lambda-cyhalothrin was the same both on the walls and roofs but different with deltamethrin and this trend in the sixth month on walls, however, mortality on the roof was the same. These results were obtained when a susceptible colony of An. gambiae sl mosquitoes was used. Our observations on DDT did not go beyond 6 months and therefore cannot be compared with observations by Taylor et al. (1981). Insecticide manufacturers claim longer residual periods on their products, making it necessary for control programmes to verify such claims. The residual effect of each insecticide formula- tion largely depends on the quality of the product (for the manufactur- er) and the quality of spraying (for control programmes). Studies on mosquito behaviour have shown that no mosquitoes were collected in huts sprayed with any of the insecticides. These results imply that mosquitoes died after getting in contact with sprayed sur- faces and therefore could not exit sprayed houses. Even if the mosqui- to population in the study villages had exophilic tendencies, they died before leaving the sprayed houses. In comparison with mosquitoes that were continuously caught from Article Table 2. Bioassays conducted on walls. Months Lambda- Deltamethrin DDT post cyhalothrin spraying 1 107/107 (100%)a 151/161 (93.8%)b 161/161 (100%)a Range (100%) Range (88-100%) Range (100%) 2 214/218 (98.2%)c 161/172 (93.6%)d 171/171 (100%)e Range (90-100%) Range (87-100%) Range (100%) 3 199/200 (99.5%)f 203/225 (90.2%)g 120/126 (95.2%)h Range (90-100%) Range (87-100%) Range (93-100%) 4 117/120 (97.5%)i 105/117 (89.7%)k 118/120 (98.3%)i Range (90-100%) Range (86-97%) Range (93-100%) 5 148/153 (96.7%)m 97/107 (90.7%)n 166/174 (95.4%)m Range (87-100%) Range (88-97%) Range (92-97%) 6 186/211 (88.2%)p 125/163 (76.7%)q 96/107 (89.7 %)p Range (81-95%) Range (72-88%) Range (80-94%) DDT, dichlorodiphenyltrichloroethane. Same letter in the same row denotes no significant difference and different letter in the same row denotes significance difference. Table 3. Bioassays conducted on roofs. Months Lambda- Deltamethrin DDT post cyhalothrin spraying 1 99/99 (100%)a 130/138 (94.2%)b 132/136 (97%)c Range (100%) Range (90-100%) Range (96-100%) 2 223/223 (100%)d 106/112 (94.6%)e 1291/131 (98.5%)f Range (100%) Range (92-100%) Range (98-100%) 3 200/203 (98.5%)g 166/179 (92.7%)h 110/114 (96.5%)i Range (90-100%) Range (88-100%) Range (90-100%) 4 170/178 (95.5%)j 112/124 (90.3%)k 103/111 (92.8%)l Range (90-100%) Range (88-100%) Range (90-100%) 5 140/151 (92.7%)m 112/128 (87.5%)n 238/256 (92.9%)m Range (88-100%) Range (85-90%) Range (90-100%) 6 224/256 (87.5%)p 138/160 (86.3%)p 24/28 (85.7 %)p Range (81-94%) Range (74-90%) Range (84-90%) DDT, dichlorodiphenyltrichloroethane. Same letter in the same row denotes no significant difference and different letter in the same row denotes significance difference. 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