Efficacy of Kamona strain Deladenus siricidicola nematodes for biological control of Sirex noctilio in North America and hybridisation with invasive conspecifics

Abstract

Sirexnoctiliois an invasive woodwasp that, along with its symbiotic fungus, has killed pine trees (Pinusspp.) in North America and in numerous countries in the Southern Hemisphere. We tested a biological control agent in North America that has successfully controlledS.noctilioin Oceania, South Africa, and South America.Deladenussiricidicolanematodes feed on the symbiotic white rot fungusAmylostereumareolatumand can switch to being parasitic onS.noctilio. When parasitic, the Kamona nematode strain can sterilise the eggs ofS.noctiliofemales. However, in North America, a different strain ofD.siricidicola(NA), presumably introduced along with the woodwasp, parasitises but does not steriliseS.noctilio. We tested the sterilising Kamona biological control strain ofD.siricidicolaagainstS.noctilioin North America. Interactions between the biological control strain and the NA strain could include competitive exclusion, co-infection within hosts or hybridisation. We rearedD.siricidicolaKamona on anA.areolatumstrain native to North America (IGS-BE) and another strain (IGS-BDF) used commercially to mass-produce the nematode in Australia. We inoculated Kamona reared on either strain ofA.areolatuminto logs infested withS.noctiliolarvae and compared parasitism rates against control logs. Individual nematodes were isolated fromS.noctiliohemocoels and from sterilised eggs and were genotyped with eight microsatellite loci. A high rate of parasitisation ofS.noctiliobyD.siricidicolaNA was found for all treatments and we found evidence of both co-infection and hybridisation. Surprisingly, sterilisation rates were not related to the rates of parasitisation byD.siricidicolaKamona.