Insecticidal effectiveness of nicotine from Nicotiana tabacum against sub-species ofAnopheles gambiae sensu lato and Anopheles funestus sensu lato (Diptera: Culicidae) from the Luapula Province of Zambia

Background: One of the main challenges affecting malaria control initiatives in sub-Saharan Africa is the swift and widespread emergence of insecticide resistance. Consequently, there is a need to explore alternative insecticides for controlling malaria vectors. This study investigated the effectiveness of tobacco extract on wild Anopheles mosquitoes during the dry season (October–November 2021) in Chebele village, Mwense District, Luapula Province, Zambia. Methods: Wild Anopheles larvae were collected using the pipetting and dipping method along the Mwense stream and reared to the F1 progeny. Wild Anopheles mosquitoes were identified using morphological taxonomic keys. Specimens belonging to the Anopheles gambiae complex and Anopheles funestus group were further identified by multiplex Polymerase Chain Reaction (PCR). The solvent extraction method was used to extract tobacco compounds from tobacco leaves. Filter papers were impregnated with clothianidin (0.132 g/ml; SumiShield® 50WG) in accordance with the World Health Organization (WHO) Standard Operating Procedure for susceptibility testing (tube tests). Clothianidin was used as a positive control, while distilled water served as a negative control. Non-blood-fed, 2- to 3-day-old female wild Anopheles mosquitoes were exposed to clothianidin (0.132 g/ml) and tobacco extract at different concentrations (25% v/v, 33.3% v/v, 50% v/v, 62.5% v/v, 71.43% v/v, and 83.3% v/v) using the World Health Organization (WHO) bottle bioassay. The insectary-reared Kisumu strain ( An. gambiae sensu stricto) was used as a reference for insecticide susceptibility tests. Results: Morphological identification of adult mosquitoes collected from 73 households showed that 98.03% were Anopheles funestus s.l. (n = 199), 1.48% were Anopheles gambiae s.l. (n = 3), and 0.49% were Culex species (n = 1). Subsequent PCR analysis of the wild-caught adult mosquitoes revealed that Anopheles funestus sensu stricto (s.s.) (n = 93; 46%) and Anopheles gambiae s.s. (n = 81; 40%) were the dominant species within the An. funestus group and the An. gambiae complex, respectively. Tobacco extract (83.3% v/v) and clothianidin (0.132 g/ml) were found to have mean knockdown rates at 80 minutes of 61.88% (95% CI: 34.03–89.74%) and 85.05% (95% CI: 72.01–98.08%), respectively. Results showed that both clothianidin and tobacco extract elicited 100% mortality in adult wild Anopheles mosquitoes and the Kisumu strain after 24 hours. The estimated LC₅₀ for tobacco extract on wild Anopheles mosquitoes was estimated to 38.77% v/v (95% CI: 9.99–55.91% v/v), as determined by probit analysis. Conclusion: The findings of this study suggest that Nicotiana tabacum leaf extract may be considered a potential bio-insecticide for controlling An. gambiae s.s. and An. funestus s.s., which are significant vectors of the malaria pathogen.