Susceptibility of Anopheles gambiae sensu lato (Diptera: Culicidae) to Permethrin, Deltamethrin and Bendiocarb in Ibadan City, Southwest Nigeria

TLDR: Bendiocarb may not be suitable as alternatives to mitigate pyrethroid resistance and a rationalised use of these insecticides coupled with regular monitoring of resistance status is essential to improve and evaluate the efficacy of the current vector control tools (ITN and IRS).

Abstract: This study was carried out to assess the resistance/susceptibility level of An. gambiae s.l, a major malaria vector in Ibadan metropolis, south west Nigeria, to two classes of insecticides approved by World Health Organization (WHO) for vector control. Anopheles larvae were collected from two communities (Ojoo and Bodija) within the metropolis and reared to adults. Two to three-day old, non-engorged female mosquitoes were exposed to discriminating dosages of 0.05% deltamethrin, 0.75% permethrin and 0.1% bendiocarb using WHO protocols and susceptibility test kits. Knockdown effect was recorded every 10 min and mortality scored 24 h after exposure. Species identification was by morphological characteristics only. The study revealed that the major malaria vector in Nigeria, An. gambiae s.l, were susceptible (mortality rate of 98.8%) to deltamethrin in Ojoo community, while Bodija recorded marginal susceptibility (87.5%). Both sites showed reduced susceptibility to permethrin and resistance to bendiocarb with 24 h post exposure mortalities ranging from 83.5 to 87.7% and 70.0 and 52.5%, respectively. The median Knockdown Time (KDT50) from 22-44.2 min for the pyrethroids (permethrin and deltamethrin), while that of carbamates (bendiocarb) range from 35.2 to 49.5 min. Resistance recorded in the field populations of An. gambiae s.l in Ibadan to bendiocarb was not observed in same population exposed to the pyrethroids (deltamethrin and permethrin) but with differential susceptibility. Therefore Bendiocarb may not be suitable as alternatives to mitigate pyrethroid resistance. A rationalised use of these insecticides coupled with regular monitoring of resistance status is essential to improve and evaluate the efficacy of the current vector control tools (ITN and IRS).