Levels of genetic diversity, population structure and introduction history of the S. noctilio-A. areolatum-D. siricidicola populations in Australasia

Sirex noctilio and its symbiotic fungus Amylostereum areolatum has threatened pine plantations in Australasia, and many other countries worldwide. The biological control nematode Deladenus siricidicola has been used to manage the populations of this pest complex for over 60 years. To gain insight into any potential ‘strains’ that may contribute to variable biocontrol success the researcher further examined the reproductive rates of nematode diversity in Australia on different fungal strains and media types.  Mitochondrial (mtCOI and mtSSU rRNA) sequence data and microsatellite markers were applied in the population genetics studies. Compared to other introduced populations worldwide, lower genetic diversity was found in Australasia, and there was no structure in populations between Australia and New Zealand.

The high level of clonality in the A. areolatum population could be exploited for the management program using the nematode by rearing the nematode on the dominant clone. The behavioral study between the lineages B and D strains of D. siricidicola indicates significant variation in the reproductive rates when feeding on four different fungal strains and two media types. Lineage D strains show higher reproductive rates than the Kamona strain and other strains in lineage B, on all treatments in our trials. Taken together, the diversity identified in D. siricidicola populations in this thesis underscores the importance of post-release monitoring in the biocontrol program.