Larvicidal Activity of Metarhizium anisopliae and Annona squamosa Leaf Extract against Culex quinquefasciatus and Anopheles gambiae Larvae

Aims: To assess the combined efficacy of Annona squamosa L. leaf extract and entomopathogenic fungus Metarhizium anisopliae against Culex quinquefasctiatus and Anopheles gambiae larvae.

Study Design: The design of the study was experimental.

Methodology: The compatibility of M. anisopliae was tested on PDA treated with 100 µg/mL of A. squamosa extract. The mosquito larvae of Cx. quinquefasctiatus and An. gambiae were exposed to An. squamosa extract at 10 µg/mL, 50 µg/mL and 100 µg/mL, M. anisopliae at 1.7 x 106 conidia/ml and 1.7 x 107 conidia/mL, and combinations of each concentration of A. squamosa and M. anisopliae.

Results: Metarhizium anisopliae was compatible with A. squamosa and gave comparable germination and proliferation as it was for blank or untreated PDA. The survival of Cx. quinquefasciatus larvae and An. gambiae larvae decreased with increase in concentration of A. squamosa extract when tested alone or when the concentration of the extract was increased at constant concentration of M. anisopliae. However, an increase in concentration of M. anisopliae at constant concentration of A. squamosa extract exhibited only slight decrease in survivals as compared to the individual M. anisopliae treatments. On day 3, survival of Cx. quinquefasciatus and An. gambiae larvae at 50 µg/mL of A. squamosa crude extract were 20% and 50% respectively. However, in a combination study, 50 µg/mL of A. squamosa when combined with 1.7 x 107 conidia/mL of M. anisopliae caused 100% mortality of An. gambiae and Cx. quinquefasciatus within 3 days while larvicidal results for conidia alone were poor even on day 3.

Conclusion: The combination of M. anisopliae and A. squamosa showed synergistic results that could be explored further for development of mosquitoes larvicidal control agent.