Population variation in traits of Deladenus siricidicola that could influence the biocontrol of Sirex noctilio in South Africa

Deladenus siricidicola is the primary biocontrol agent of the invasive woodwasp, Sirex noctilio. The nematode is mass-reared in culture on the S. noctilio symbiotic fungus, A. areolatum, but can also be induced to convert into its infective form in culture. The aim of this study was to explore the level of variation among a collection of D. siricidicola strains to convert into the infective form in culture. In addition, we measured variation in growth of the nematode on a strain of A. areolatum that is commonly used for laboratory rearing. Both traits could influence laboratory rearing and efficiency in the field. The 22 strains from three countries showed significant variation in the frequency of conversion into the infective form in culture. Even genetically uniform strains from South Africa displayed a range of variation in this trait. There was also significant variation in the growth of D. siricidicola on A. areolatum. These results emphasise the importance of considering variation in traits in D. siricidicola that could influence a biological control program. They also provide tools that could be used to screen larger collections of D. siricidicola for variation in traits linked to virulence and reproduction.