The influence of Amylostereum areolatum diversity and competitive interactions on the fitness of the Sirex parasitic nematode Deladenus siricidicola

摘要

The Sirex noctilio (woodwasp)–Amylostereum areolatum (fungus) complex has caused substantial losses topine industries in its introduced range. The nematode Deladenus siricidicola that parasitizes S. noctilio andfeeds on A. areolatum is widely used as a biological control agent for S. noctilio, but not with consistentsuccess. This variable success could be due to factors that influence the feeding and reproductive abilityof the nematode on A. areolatum.We test two main hypotheses that emerge from this prediction. First, wecompared the survival of D. siricidicola on the South African field strain and the Australian laboratorystrain of A. areolatum, to examine a possible incompatibility between nematode and fungal strain. Second,we examined the competitive interactions of these two A. areolatum strains with two common sapstainfungi, Diplodia pinea and Ophiostoma ips, that occur in S. noctilio infested trees in South Africa. The effect ofwater potential on the outcome of these fungal interactions was also considered. The data showed thatD. siricidicola survives at comparable levels on the two A. areolatum strains. Water potential of the mediasignificantly influenced growth of the fungi and their ability to capture host resource in competitiveinteractions. D. pinea competed increasingly better against A. areolatum with decreasing water potential.The results suggest that competitive interactions between A. areolatum and sapstain fungi could negativelyinfluence the success of D. siricidicola, especially under conditions of lowered water potential.