Lasiodiplodia theobromae and the roles of insects in dispersal of the fungi

摘要

Lasiodiplodia theobromae GK-1, a strain isolated from the surface of fruit of the coconut palm,produced acoconut-like aroma that was identified as 2-octeno-propor.to-lactone, #beta#-phenylethanol,and a compound known as mellein. Considering the general nature of the secondary metabolite and its potential role for the microorganisms producing it, this aromatic compound might have ecological significance as an attractant for insects, which could then be vectors of the fungal spores., This hypothesis led to isolation of L.theobromae from the outer surface of a danaid butterfly, Idea leuconoe, which was caught in an area in which there were many plants infected by L.theobrmae. Mellein uptake was investigated by studying the ingesting behaviour of danaid butterflies (male only) alighting on fungal-infected plant tissues in the field and in an insectarium. These observations indicated some kind of mutualistic relationship between the butterfly and L.theobraomae, associated with the mellein.Mellein was not major component in the hairpencil (a kind of sex organ), and the butterfly could breed without the mellein in an insectarium, suggesting the insect could be independent of L.theobromae. This also suggested the role of the insect in dispersing the fungi may be rather weak. On the other hand, the fact that the plant tissues infected with L.theobromae outdoors were rather sound in appearance might indicate a symbiotic relationship between plant and fungi which could produce a plant hormone of some kind. This also suggests a useful application of the fungus for postharvest disease control.