Host–parasitoid interaction as affected by interkingdom competition

Abstract

Although still underrepresented in ecological research, competitive interactions between distantly related organisms (so-called "interkingdom competition") are expected to be widespread in various ecosystems, with yet unknown consequences for, e.g. trophic interactions. In the model host-parasitoid system Drosophila melanogaster-Asobara tabida, toxic filamentous fungi have been shown to be serious competitors that critically affect the density-dependent survival of host Drosophila larvae. This study investigates the extent to which the competing mould Aspergillus niger affects key properties of the well-studied Drosophila-parasitoid system and how the host-parasitoid interaction influences the microbial competitor. In contrast to slightly positive density-dependent host mortality under mould-free conditions, competing A. niger mediated a strong Allee effect for parasitised larvae, i.e. mortality decreased with increasing larval density. It was found that the common toxic fungal metabolite kojic acid is not responsible for higher death rates in parasitised larvae. Single parasitised Drosophila larvae were less harmful to fungal reproduction than unparasitised larvae, but this effect vanished with an increase in larval density. As predicted from the negative effect of fungi on host survival and thus on parasitoid fitness at low larval densities, A. tabida females spent less time foraging in fungus-infested patches. Interestingly, even though high host larval densities increased host survival, parasitoids still reduced their search efforts in fungus-infested patches, indicating a benefit for host larvae from feeding in the presence of noxious mould. Thus, this experimental study provides evidence of the potentially important role of interkingdom competition in determining trophic interactions in saprophagous animal communities and the dynamics of both host-parasitoid and microbial populations.

Fruit, flies and filamentous fungi - experimental analysis of animal-microbe competition using Drosophila melanogaster and Aspergillus mould as a model system

“…Such a communal insect attack on mould fungi may enable larvae to interfere with fungal colonies, suppress fungal growth and hence improve their own survival. In turn, fungi are known to synthesise secondary chemicals which they secrete into their growing substrate, and many of these fungal secondary metabolites have been shown to have insecticidal properties (Reiss 1975, Melone and Chinnici 1986, Rohlfs 2008, Rohlfs and Obmann 2009). Thus, one prominent hypothesis states that toxic secondary metabolites protect fungi from antagonistic animals by deterring and/or harming them.…”

Species-specific responses of dew fly larvae to mycotoxins

“…Therefore, fungal natural products have the potential to control population dynamics of saprophagous insects, and their deleterious effect has been demonstrated to affect higher trophic levels (such as parasitic wasps) in these insect communities (Rohlfs 2008).…”

Odor-mediated aggregation enhances the colonization ability of Drosophila melanogaster

“…Furthermore the larva of D. melanogaster themselves are also able to suppress fungal growth by disrupting the hyphae of the fungus. Larger groups of larva are more successful at this than smaller groups or single larvae (Rohlfs et al, 2005, Rohlfs, 2008. The local interaction with the fungi gives rise to an Allee effect in larval development.…”