Evidence of Insecticide Resistance to Pyrethroids and Bendiocarb in from Tsararano, Marovoay District, Madagascar.

Introduction: In Madagascar, malaria control relies on the countrywide use of long lasting insecticide treated bed nets (LLINs) and on indoor residual spraying (IRS) in the central highland area as well as a small area on the eastern coast. We tested insecticide resistance mechanisms of from Tsararano, a malaria endemic village in the coastal health district of Marovoay.

Methods: Insecticide susceptibility bioassays were done in July 2017 on first-generation (F1) to assess (i) the susceptibility to permethrin (0.05%), deltamethrin (0.05%), DDT (4%), malathion (5%), fenitrothion (1%), and bendiocarb (0.1%); (ii) the effect of preexposure to the piperonyl butoxide (PBO) synergist; and (iii) the enzymatic activities of cytochrome P450, esterases, and glutathione S-transferases (GST).

Results: Our results demonstrated that . was phenotypically resistant to pyrethroids and bendiocarb, with a mortality rate (MR) of 33.6% (95%CI: 24.5-43.7%) and 86% (95%CI: 77.6-92.1%), respectively. In contrast, . were 100% susceptible to DDT and organophosphates (malathion and fenitrothion). Preexposure of . to PBO synergist significantly restored the susceptibility to bendiocarb (MR=100%) and increased the MR in the pyrethroid group, from 96% (95%CI: 90.0-98.9%) to 100% for deltamethrin and permethrin, respectively ( = 43, = 3, ). Enzymatic activities of cytochrome P450 and -esterases were significantly elevated among . compared with the IPM strain (Mann-Whitney = 30; = , respectively). No significant differences of -esterases activities compared to the IPM reference strain were observed (Mann-Whitney ).

Conclusion: In Tsararano, despite the absence of an IRS programme, there is evidence of high levels of insecticide resistance to pyrethroids and bendiocarb in .