Insect Vectors

Some wood-decay fungi are dispersed by insects (Chapter 9), which influences the structure and dynamics of populations of mycelia. The relationship between the insects and fungi varies between being ephemeral to almost total ecological dependence with highly adapted morphological specializations from both partners. An example of low specificity is when wood-boring insects feed on spores of decay fungi and passively carry some spores to the next woody resource visited. A high degree of specialization is seen in the wood wasp-Am-ylostereum relationships (Slippers et al., 2003). Several species of Sirex and Urocerus gigas are mutualistically associated with A. areolatum (Sirex) and A. chailletii (Urocerus). Arthrospores are carried in mycangia inside the body of the females. The spores are inoculated into wood during oviposition. Ramets of a single genet of A. areolatum have been isolated from trees scattered in a single forest and from points widely separated geographically in Lithuania, Sweden and Denmark (Vasiliauskas et al., 1998). The dependence of the fungus in northern Europe on insect vectored spread is further illustrated by the fact that fruit bodies are very seldom encountered. There is less emphasis on vertical transmission in A. chailletii (Vasiliauskas and Stenlid, 1998). Here ramets are also distributed over large areas, but the higher genotypic variation in the fungus indicates that the insects occasionally pick up new genotypes that have gone through meiosis. The Sirex-Amylostereum system can cause significant damages to conifer plantation (Slippers et al., 2003). The life cycles of the Sirex-Am-ylostereum symbionts, where larval development can go on unspotted for 1-3 years, makes the system easy to spread in trade. S. noctilio-A. aerolatum has been introduced into the southern hemisphere where they cause massive problems to Pinus plantation forestry. The population structure is highly clonal with essentially the same genet being spread to millions of trees in South Africa, Australia, New Zealand, Chile and Uruguay.

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