Collembolans as vectors of entomopathogenic fungi

The aim of the study was to compare the ability of collembolan species to transmit the three entomopathogenic fungi Beauveria bassiana, B. brongniartii and Metarhizium anisopliae to a susceptible host, Tenebrio molitor. The three collembolan species Folsomia fimitaria, Hypogastrura assimilis and Proisotoma minuta were all able to transmit sufficient inoculum to directly cause infection in a susceptible host after exposure to soil containing conidia. However, their ability differed significantly, with transmission by P minuta causing the lowest mortality while there was no significant difference between F fimetaria and H. assimilis. The mortality of T molitor increased with the concentration of conidia the collembolans had been exposed to for all combinations of fungi and collembolan species studied. The two species F fimetaria and H. assimilis were able to transmit enough inoculum after exposure for 24 h to soil containing 10(6) conidia g(-1) to cause low infection levels in T molitor, while transmission by P minuta only occurred after exposure to soil containing 10(7) conidia g(-1). The infection level in T molitor increased with the duration of the prior exposure of the collembolans to soil containing 10(7) conidia g(-1) wet weight and both F fimetaria, and H. assimilis carried enough inoculum after only 30 min exposure to subsequently cause infection in T molitor. For all three species the mortalities of T molitor only differed significantly from the control after 24 h of exposure. When the potential of the three species as vectors was compared by transferring a range of numbers of F fimitaria, H. assimilis and P minuta previously exposed to sporulating fungal material, P minuta was found to cause a significantly lower infection levels than equal numbers of F fimetaria and H. assimilis. However, based on estimated total fresh weight of the collembolans, there was no significant effect of collembolan species. This suggests that the difference between the three tested collembolan species in their ability to vector entomopathogenic fungi is mainly due to the difference in their body size and thus the total amount of conidia they are able to transport, and not physiological or morphological differences affecting viability of the conidia.