Ecological determinants of fungal infections in folivorous moths

Natural enemies shape the fate of species at both ecological and evolutionary time scales. While the effects of predators and parasitoids on insects are well documented, much less is known about the ecological and evolutionary role of entomopathogenic fungi. In particular, it is unclear to which extent may the spatiotemporal distribution patterns of these pathogens create selective pressures on ecological traits of herbivorous insects, determining where and when is life the safest. In the present study, we reared three lepidopteran species (Acronicta rumicis L., Cabera pusaria L. and Hypomecis atomaria Hübner) in seminatural conditions in an European hemiboreal forest habitat. The probability of the insects to die from fungal infection was studied as dependent on insect species, food plant of the insect, study site, (manipulated) condition of the larvae and the phenological phase. In the course of rearing, visually detectable fungal infections were isolated and identified. The prevalence of entomopathogenic fungi remained low to moderate with the value consistently below 10% across the subsets of the data while as many as 23 fungal species, primarily belonging to the families Cordycipitaceae, Aspergillaceae and Nectriaceae, were recorded. There were no major differences among the insect species in prevalence of the infections or the structure of associated fungal assemblages. The obligatorily entomopathogenic family Cordycipitaceae dominated among the pathogens of pupae but not among the pathogens of larvae. Overall, there was evidence for a relatively weak impact of ecological factors on the probability to be infected by a fungal pathogen; there were no effects of host plant, study site or phenology which would be consistent over the study species and developmental stages of the insects. Nevertheless, when analyses were done using particular fungal taxa were examined separately, Akanthomyces muscarius was found to infect insects fed with leaves of only one of the host plant speciess, Betula sp.. This demonstrates that it is possible that feeding on some host plant species has fitness costs mediated by pathogenic fungi showing that fungus-mediated effects on insect life history traits are well possible, and deserve attention.