Insecticidal and biological effects of three plant extracts tested against the dengue vector, Stegomyia agyptii (Diptera: Culicidae)

Development of resistant in vectors especially vector mosquitoes are becoming a challenge for the scientific community for management and control mosquito population. Vector mosquitoes are likely to withstand toxicity and develop resistant mechanism to single active compound hence, combining medicinal plants with rich active compounds stops resistant development and proliferation of mosquitoes. In this study we put effort to evaluate the effect of methanol extract of Tagetes patula, Clerodentron phillomedis, and Catharanthus roseus in individual and in combination against the dengue vector, Stegomyia agyptii. Lethal concentrations (LC₅₀ and LC₉₀) were calculated to find out the effect of the test plants in individual and in combination. T. patula extract showed vaguely higher mortality rate when compared to C. phillomedis, and C. roseus but there was no significant variation among the three test plants. The median LC of combined treatment showed a significant difference between the combined (2.25 µg/mL/3^rd instar) and individual treatment (6.41 µg/mL/3^rd instar for T. patula, 6.85 µg/mL/3^rd instar for C. phillomedis and 6.59 µg/mL/3^rd instar for C. roseus). The combined efficacy of three test plants was also effective in controlling vector mosquitoes at fields with different agro-climatic conditions. The study proves that the combination of T. patula, C. phillomedis, and C. roseus is effective in different field conditions at lower concentrations.