Larvicidal Activity of Some Heterocyclic Thiosemicarbazones and Semicarbazones Derivatives Against Anopheles arabiensis Larvae

Abstract

Malaria remains one of the most significant vector-borne diseases worldwide and is transmitted through the bites of infected female Anopheles mosquitoes. The increasing prevalence of insecticide resistance has substantially compromised the effectiveness of conventional chemical control measures, necessitating the development of novel, potent, and environmentally sustainable larvicides. In this study, the larvicidal activity of three thiosemicarbazone derivatives (TS1–TS3) and three semicarbazone derivatives (SC1–SC3) was evaluated against Anopheles arabiensis larvae following standard World Health Organization (WHO) bioassay procedures. Larvae were exposed to different concentrations of the tested compounds, and mortality rates were recorded after 24 and 48 h of exposure. Lethal concentration (LC₅₀) values were estimated using probit and logit analyses. The thiosemicarbazone derivatives exhibited clear concentration- and time-dependent larvicidal activity, whereas the semicarbazone derivatives exhibited no detectable larvicidal activity under the tested conditions. Among the active compounds, TS3 demonstrated the highest potency, with the LC₅₀ value decreasing markedly from 248 ppm after 24 h to 107 ppm after 48 h of exposure. Statistical analysis revealed strong mortality–concentration relationships, with coefficients of determination (R²) equal to or greater than 0.80. These findings indicate that the larvicidal activity observed in this study was restricted to thiosemicarbazone derivatives, while semicarbazone derivatives were inactive against An. arabiensis larvae under the tested conditions. Thiosemicarbazone derivatives therefore represent promising candidates for mosquito control programs, although further studies on structural optimization, mode of action, and environmental safety are required before practical application.