BIOLOGY AND ECOLOGY OF SIREX, DELADENUS AND AMYLOSTEREUM IN NORTH AMERICA

Sirex noctilio is a woodwasp that attacks stressed or dying pine trees. It is native to Eurasia and North Africa but has been invasive in the southern hemisphere since the early 1900s. It was found for the first time in the United States in New York State in September 2004 and in Ontario in 2005. Since then it has spread to a total of seven northeastern US states. S. noctilio is more aggressive than the native pine specialist Sirex nigricornis and it is able to kill living pines by injecting a phytotoxic venom and its symbiotic fungus Amylostereum areolatum into tree trunks. The Kamona strain of the nematode Deladenus siricidicola has been extensively used as a biological control agent against invasive S. noctilio in the Southern Hemisphere, where it sterilizes female hosts by entering the eggs and making them inviable. In North America, a non-sterilizing (NS) strain of D. siricidicola, thought to have been introduced with S. noctilio, is commonly found parasitizing this invasive woodwasp. Species of Deladenus that parasitize Sirex have a parasitic form as well as a mycophagous form. Studies were conducted to understand 1. Sirex mating behavior and sexual receptivity, 2. the growth of two strains of D. siricidicola, Kamona and NS, with different strains and species of Amylostereum spp. for food, and 3. the use of D. siricidicola and Deladenus proximus, a native species of nematode in North America found associated with S. nigricornis, as biological control agents for S. noctilio as well as potential impacts caused by D. siricidicola on the native species of woodwasp S. nigricornis. When we conducted trials with 10 males per female in cages in the shade, sexual receptivity of S. noctilio females was mainly driven by temperature, with increased mating when it was warm. Mating always occurred in the section of the cage toward sunlight. Mycophagous forms of the two D. siricidicola strains displayed relatively similar production of offspring when feeding on most of the A. areolatum strains found associated with S. noctilio in this continent, except for strain BD on which NS produced more offspring than the biological control strain Kamona. Growth of both nematodes was greater on the introduced versus the native A. areolatum isolates. When testing D. siricidicola Kamona and D. proximus for potential control of S. noctilio, very low infection with Kamona was found, and when females were infected with this nematode the percentage of egg sterilization was usually not high. None of the wasps of either species were infected with D. proximus. When D. siricidicola Kamona was tested against S. nigricornis none of the wasps emerging from treated logs were infected. These findings suggest that further studies on the use of nematodes to control S. noctilio in North America are necessary. Possibly studying new strains of D. siricidicola would result in discovery of a strain of this nematode with higher efficacy in controlling the invasive woodwasp S. noctilio in North America