Entomopathogenic fungi associated with Stomoxys calcitrans in Slovakia and efficacy of local fungal strains against the stable fly

The stable fly, Stomoxys calcitrans , is the most important ectoparasite of livestock throughout the world. Entomopathogenic fungi are natural antagonists of stable flies with the potential to be used as biocontrol agents in integrated management programmes of this pest. The prevalence and species diversity of entomopathogenic fungi in stable fly populations were documented on a dairy cattle farm in south-western Slovakia. The prevalence of fungal infection was low and the maximum percentage of infected flies reached 2.72% during May–October in 2016. Three Beauveria species were identified from infected flies, B. bassiana , B. pseudobassiana and B. brongniartii . Beauveria pseudobassiana and B. brongniartii are reported from S. calcitrans for the first time. In laboratory tests, the pathogenicity of four entomopathogenic fungi B. bassiana , B. pseudobassiana , M. anisopliae and Isaria fumosorosea against adult stable flies was compared. The flies were susceptible to infection by the fungi and the most virulent isolate of B. bassiana (IKEP10) was selected for spore formulation testing and field trials. We tested three types of spore formulations and the aqueous spore suspension was more effective against stable flies than spores formulated in the powder or oil suspension. Repeated treatments of the interior of the stable with B. bassiana spores at fortnightly intervals during June–August resulted in a 10 times higher prevalence of fungal infection in the stable fly population compared with the untreated stable, but the treatments did not effectively reduce the fly population. The selected B. bassiana isolate may represent an interesting tool in the biocontrol of stable fly populations, but further experiments are needed to design an appropriate formulation and enhance its efficacy.