A comparative study of the phytotoxic effects of siricid woodwasps on conifers

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Abstract
SUMMARY: The effects of siricid mucus and the symbiotic fungus injected artificially, or by oviposition of caged females on young conifer trees were investigated in a comparative study of the phytotoxicity caused by seven species of siricid woodwasps. Dilute solutions of mucus were bioassayed using detached shoots. Rapid physiological changes in the radial growth of the stem, quantity of starch in the leaves, leaf pressure and colour of the foliage of living trees were induced by only one species, Sirex noctilio. Solutions of S. noctilio and S. cyaneus mucus caused premature senescence of needles on detached shoots. The other species, Sirex juvencus, Urocerus gigas, U. augur, U. sah and Xeris spectrum, produced no phytotoxic symptoms in living trees and less rapid senescence of needles on detached shoots. These differences are discussed in relation to the ecology of siricids in the northern hemisphere and the successful establishment of S. noctilio in pine plantations of Australasia.

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