Abstract
We hypothesize that differences in fungal taxonomic groups may exert a direct influence on the composition of myco- phagous insect communities, and that the relative importance of taxonomy compared to other fungal traits may change as the mush- rooms decay. We conducted a 3-year field survey and analyzed the species composition of mycophagous insect communities using partial canonical correspondence analysis (partial CCA). We collected 2457 mushrooms belonging to 27 genera, and 4616 insects belonging to 16 families emerged from 439 of the mushrooms. For the whole insect community, fungal genera explained 10-19% of the total variance in the family composition of the insect communities of mushrooms at different developmental stages. Only the fungal genus Collybia significantly affected the community composition almost irrespective of developmental stage. In the droso- philid community, which consisted of 844 individuals from 9 species, fungal genera explained 19-34% of the total variance. Some fungal genera, such as Amanita and Collybia, affected the drosophilid community, but not at all developmental stages. The number of fungal genera that significantly affected the insect community composition did not differ among fungal stages both in the whole insect community and in the drosophilid community. Thus, our former hypothesis was supported by the present analysis, whereas the latter was not. However, the percentages of variance explained by fungal genera were rather small. This suggests that the importance of fungal genera is likely to be less significant than that of other selection pressures in determining the species composition of myco- phagous insect communities.
Highlights
Mycophagous insects are generally recognized as polyphagous insects (Hackman & Meinander, 1979; Hanski, 1989), and Hanski (1989) proposed two compatible hypotheses to explain why polyphagy is widely observed in mycophagous insect communities
Because we aimed to reveal the effect of fungal quality, indicated by fungal genera, and developmental stage, on the species composition of mycophagous insect communities, it was important to exclude as many other factors as possible and a partial correspondence analysis (CCA) was performed
Our hypothesis that a difference in the fungi may exert a direct influence on the composition of mycophagous insect communities was supported, but the other hypothesis that the relative importance of fungal genera compared to other fungal traits may change as the mushrooms decay was not supported by our analyses
Summary
Mycophagous insects are generally recognized as polyphagous insects (Hackman & Meinander, 1979; Hanski, 1989), and Hanski (1989) proposed two compatible hypotheses to explain why polyphagy is widely observed in mycophagous insect communities. Species composition of mycophagous insect communities differ depending on the traits of the fruiting bodies they use; the tough and long-lived fruiting bodies of Aphyllophorales (bracket fungi) versus the fragile and ephemeral ones of Agaricales (mushrooms). Many studies have revealed that insects feeding on bracket fungi are generally mono- or oligophagous beetles (Ashe, 1984; Lawrence, 1989; Komonen, 2001), whereas those feeding on mushrooms are generally polyphagous flies (Hackman & Meinander, 1979; Hanski, 1989). Jonsell & Nordlander (2004) surveyed the mycophagous beetles feeding on bracket fungi and proposed that polyphagous insects use decaying fruiting bodies to avoid the fungal chemical defenses (Kukor & Martin, 1987). It is proposed that these fungal insecticides do not affect mycophagous insects that are adapted to them (Jaenike et al, 1983; Hanski, 1989), but these studies did not take into account the state of decay of the mushrooms
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