RESUMO
Insecticide resistance in mosquitoes is increasing amidst growing cases of global malaria, leading to high fatality in mostly Africa. To overcome the resistance as well as environmental effects of the synthetic insecticides, preliminary insecticidal and botanical potentiating effects of sub-lethal concentration (LC25) Ficus sycomorus active fraction (AFFS) and its synergistic potential with standard insecticide permethrin were evaluated against malarial vector Anopheles coluzzii (Coetzee & Wilkerson) populations. The glutathione-S-transferase (GST) inhibitory activity of the AFFS was also investigated compared to standard GST inhibitor, diethyl meleate (DEM). The WHO standard protocol for adult bioassay was used to expose the adult mosquitoes with sub-lethal concentration (LD25=0.49 mg/ml) of the plants' active fraction and permethrin (0.75%). The permethrin susceptibility screening result showed high level of resistance to permethrin in the field populations of A. coluzzii from Kano with 50.29 ± 2.14% average mortality after exposure to WHO diagnostic dose 0.75% permethrin. Post hoc Fisher's exact test showed that combination of sub-lethal concentration of AFFS with permethrin (mortality=73.02±12.10%; p=0.00352; RR=0.6923 and 95% CI = 0.5358-0.8946) was statistically significant, while the combination of sub-lethal concentration of AFFS with DEM showed no statistical difference (mortality=63.22±5.03; p=1; RR=0.6667 and 95% CI=0.4470-0.8438). This potentiation effect was signified to be additive effects with co-toxicity factor (CTF) of - 12.66. There was significant reduction of GST activities in the AFFS- and permethrin -exposed groups compared to unexposed populations of A. coluzzii (p < 0.05). The AFFS additively potentiate the permethrin activities by inhibiting GSTs, bio-transformational enzymes implicated in pyrethroids resistance. This study finding generally signifies the potential for bio-rational insecticide approach for malarial vector control.
