Larvicidal activities of chinaberry,neem and Bacillus thuringiensis israelensis(Bti) to an insecticide resistant population of Anopheles arabiensis from Tolay,Southwest Ethiopia

Objective:To elucidate the larvicidal potency of neem, chinaberry and Bacillus thuringiensis israelensis(Bti) to larvae of Anopheles arabiensis under semi-field condition and adult susceptibility/resistance to the conventionally used insecticides in Tolay,Southwestern Ethiopia.Methods: Wild collected 3rd and 4th stage larvae were exposed to neem, and chinaberry seed powder dissolved in water and Bti in artificial containers at three treatment levels:0.2, 0.1 and 0.05 g/m^2 and controls were free of treatments. Larval and pupal mortalities were monitored daily and residual activities were determined. The experiments were replicated three times. The World Health Organization tube test for all classes of insecticides was conducted on adult Anopheles arabiensis reared from field collected larvae and pupae. Data were analyzed using STATA software version 11.Results: In the first application, neem powder caused 88.9%, 87.9% and 79.4% larval and pupal mortality at 0.2, 0.1 and 0.05 g/m^2 after 4.3, 6.0 and 5.7 days, respectively. The corresponding killing effect of chinaberry was 80.3%, 62.1% and 30.3% after 7.0, 7.7 and 8.3days respectively. Bti at all treatments killed 100% after 24 h except 2.7 days for 0.05 g/m^2.Adult mosquitoes were susceptible only for fenitrothion and pirimiphos-methyl with 100%mortality while resistant to deltamethrin, alpha-cypermethrin, etofenprox and dichlorodiphenyl-tricgloroethane with only 9.0%, 3.0%, 5.1% and 2.0% mortalities respectively.Conclusions: Neem, chinaberry and Bti showed potent larvicidal and pupicidal activities. However, in the area, high level of mosquito resistance to pyrethroids and dichlorodiphenyl-tricgloroethane was seen which will pose serious challenge to vector control in the future. Therefore, using integrated approach including these botanical larvicides is warranted to manage insecticide resistance.

Effects of environmental modification on the diversity and positivity of anopheline mosquito aquatic habitats at Arjo-Dedessa irrigation development site,Southwest Ethiopia

Background:Irrigated agriculture is key to increase agricultural productivity and ensure food security in Africa.However,unintended negative public health impacts(e.g.malaria)of such environmental modification have been a challenge.This study assessed the diversity and distribution of breeding habitats of malaria vector mosquitoes around Arjo-Dedessa irrigation development site in Southwest Ethiopia.Methods:Anopheline mosquito larvae were surveyed from two agroecosystems,‘irrigated’and‘non-irrigated’areas during the dry(December 2017–February 2018)and wet(June 2018–August 2018)seasons.Mosquito habitat diversity and larval abundance were compared between the irrigated and non-irrigated areas.The association between anopheline mosquito larvae occurrence and environmental parameters was analysed using Pearson chisquare.Multiple logistic regression analysis was used to determine primary parameters that influence the occurrence of anopheline larvae.Results:Overall,319 aquatic habitats were surveyed during the study period.Around 60%(n=152)of the habitats were positive for anopheline mosquito larvae,of which 63.8%(n=97)and 36.2%(n=55)were from irrigated and non-irrigated areas,respectively.The number of anopheline positive habitats was two-fold higher in irrigated than non-irrigated areas.Anopheline larval abundance in the irrigated area was 16.6%higher than the non-irrigated area.Pearson’s chi-square analysis showed that season(χ2=63.122,df=1,P<0.001),agroecosystem(being irrigated or non-irrigated)(χ2=6.448,df=1,P=0.011),and turbidity(χ2=7.296,df=2,P=0.025)had a significant association with larval anopheline occurrence.Conclusions:The study showed a higher anopheline mosquito breeding habitat diversity,larval occurrence and abundance in the irrigated than non-irrigated areas in both dry and wet seasons.This indicates that irrigation development activities contribute to proliferation of suitable mosquito breeding habitats that could increase the risk of malaria transmission.Incorporating larval source management into routine malaria vector control strategies could help reduce mosquito population density and malaria transmission around irrigation schemes.