Neem extract (Azadirachta indica) synergizes the entomopathogenic effect of Metarhizium anisoplia against malaria vector; Anopheles stephensi

Background: Malaria is of a long history in Iran and still has strong foothold in the south and southeast of the country as an endemic disease. Anopheles stephensi is one of the main vectors of malaria in Iran. The use of insecticides remains the most effective strategy control vectors, but of course problematic.Objectives: This study aimed to examine the efficacy of the entomopathogenic fungus, Metarhizium anisopliae, in combination with neem extract as an alternative safe measure. Materials and Methods: A. stephensi was reared at 28°C, 80% RH and 12:12 L/D. In the first set of experiments, the 3rd and 4th instar larvae were exposed to neem extract at different concentrations rating from 185 to 264 ppm and LC50 and LD90 values determined. In the second set of experiments, the larvae were subjected to different spore concentrations ranging from 5 × 103 to 5 × 104 spore/ml. The larval mortality were then recorded for one week and LC50 values calculated. To assess the synergistic effects, neem extract was used at 93-278 ppm in combination with sub-lethal dose of fungal spores at 0.5 × 104 spore/ml .Results: The fungus caused high mortality to A. stephensi larvae with LC50 value equal to 3.8 × 104 spore/ml and LT50 equal to 2.5 days. The fungus, also, exhibited delayed effects inflicting pupal mortality and reduced blood feeding and fecundity at adult stage. However, neem extract has no negative effects of fungal growth in culture media even at concentration exceeding 500 ppm. Combining lower doses of neem extract with fungal spores not only had no antagonistic effects but showed synergism. In fact, the combination of 178 and 122 ppm neem extract lowered the LC50 value of the fungus to 0.5 × 104 spore/ ml measured at 2 and 5 day post-treatment respectively. The estimated synergistic factor (SF) of combined neem extract and fungal spore was more than unity (1.3). This, therefore, supports the synergism.Conclusion: The fungus Metarhizium anisopliae showed a high bio-insecticidal effect on Anopheles stephensi either as a standalone agent or in combination with neem extract.

کلیدواژه ها:

Biological control - Anopheles stephensi - Metarhizium anisopliae - Neem extract - synergistic effect ، IVM