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Experiments in coltrolled environments were conducted to verify the parasitic action of Helicotoylenchus dignicus on Pinus strobus, P. excelsa and their hybrid. After nine months the increase of nemetode populations indicates a positive host-parsite relationship. In general the consequences of nematode feeding is a reduction of the seedling development similar to that induced by the absence of mycorrhizae. The nematode, a migratory ectoparasite, feeds on the mycorrhizae but perefers non-mycorrhized regions of the absorptive roots thereby delaying or preventing the development of the mycorrhizae and weakening the long roots. This may exercise a negative effect on root growth and therefore the vigour of the seedlings which require symbiosis to maintain normal development. [ABSTRACT FROM AUTHOR]