A study on avoidance and repellency of the African malaria vector Anopheles gambiae upon exposure to the entomopathogenic fungus Metarhizium anisopliae

Metarhizium anisopliae is being considered as a biocontrol agent against the adult stage of the malaria mosquito Anopheles gambiae. In the current study we investigated behavioral effects of female An. gambiae in the presence of the fungus. In three different bioassays we tested whether the behaviour of female An. gambiae s.s. mosquitoes was affected by conidia of the entomopathogenic fungus M. anisopliae. From two bioassays where mosquitoes (1) were allowed to escape from a cylinder containing dry conidia, and (2) could choose between two cages (one containing dry conidia, the other not) to feed from a glucose-solution, it became clear that dry conidia have a significant repelling effect (p<0.05). When conidia were applied in a suspension of 8% adjuvant vegetable-oil formulation and impregnated on paper, it appeared that these oil-treated conidia had no repelling effect (p=0.205). In addition to the already known positive effects of suspending conidia in oil (preventing conidia from becoming airborne and protection from drying out), we here show another positive effect, namely absence of repellency, suggesting that in field applications the conidia should be oil-formulated.