Pathogenicity and attractiveness of entomopathogenic hyphomycete fungi to collembolans

Abstract

The aim of the present study was to test the pathogenicity of hyphomycete entomopathogenic fungi used for biocontrol to non-target euedaphic collembolans, and to test the behavioural responses of collembolans to the presence of these fungi. In order to do this, adults of the three collembolan species Folsomia fimetaria, Hypogastrura assimilis and Proisotoma minuta were inoculated by dipping in a 1×10 7 conidia ml −1 suspension of three entomopathogenic fungi Beauveria bassiana, Beauveria brongniartii and Metarhizium anisopliae, and for F. fimetaria additionally in 1×10 8 conidia ml −1 suspensions. None of the fungal isolates increased the mortality of any of the three tested collembolans compared to an uninoculated control. The effect of continuous exposure to conidia of B. brongniartii and M. anisopliae in the substrate was tested by incubating adult F. fimetaria and P. minuta for 14 days at 20 °C in sphagnum containing 1×10 8 conidia g −1 wet weight. In contrast to direct inoculation, the exposure of F. fimetaria to sphagnum inoculated with one of the B. brongniartii isolates and M. anisopliae was found to increase mortality significantly from 17.3% in the control to 56.9 and 41.8% respectively, while there was no significant difference between the mortalities in any of the other treatments. The behavioural response of the collembolans to the presence of conidia in the substrate was tested in pair-wise comparisons between the three entomopathogens and baker’s yeast. In addition, a test of the response of the collembolans to an increasing gradient in concentration of conidia in the substrate was performed. In the pair-wise comparison, the order of attractiveness was similar for the three collembolan species with B. brongniartii being the most preferred and B. bassiana as the least. B. brongniartii was found to be more attractive than baker’s yeast to all three collembolan species. When exposed to a gradient of conidial concentration, the highest numbers of collembolans were recorded on the highest concentrations of all three fungi. It can be concluded that entomopathogenic hyphomycete fungi used as biocontrol agents are of low virulence to non-target euedaphic collembolans, although the susceptibility of the tested collembolan species and the virulence of isolates varied significantly. The attraction of the collembolans to the fungi is likely to increase the dispersal of these fungi in soil.