Virulence of Metarhizium anisopliae to Eggs and Immature Stages of Stomoxys calcitrans

Stomoxys calcitrans control is primarily based on the use of chemical products; however, new methods for control have been investigated. Biological control has been proposed as a promising alternative to traditional chemicals. The current study evaluated three methods in vitro to treat S. calcitrans eggs with the fungus Metarhizium anisopliae and assessed the virulence of this fungus to immature stages of this fly. In the first method of egg exposure, eggs were immersed in conidial suspensions and transferred to Petri plates with high humidity. A high mortality was observed in both treated and control groups. In the second method, the eggs were transferred to rearing medium right after immersion in conidial suspensions; the suspensions with highest conidial concentrations, 107 and 108 conidia mL−1, caused 96.25% and 100% mortality, respectively. In the third method, the eggs were sprayed with conidial suspensions on the rearing medium. A high mortality was observed at 107 and 108 conidia mL−1, 78.3% and 100%, respectively. The second method had the lowest mortality in the control group and was considered the most useful method for evaluating the effect of entomopathogenic fungi on S. calcitrans eggs. While eggs were very susceptible to M. anisopliae infection, larvae and pupae were not.