Genetic variability among native and introduced strains of the parasitic nematode Deladenus siricidicola.

Sirex noctilio is an invasive Eurasian woodwasp that can kill pine (Pinus spp.) trees and has been introduced to areas of the Southern Hemisphere where plantations of introduced pines are grown. The main method of control of this invasive pest has been introduction and augmentation of a parasitic nematode, Deladenus siricidicola. The strain of D. siricidicola used for biological control of S. noctilio in the Southern Hemisphere originated in Sopron, Hungary. The genotype of D. siricidicola used for biological control sterilizes females of the strain of S. noctilio present in Australia. However, different strains of S. noctilio have been introduced to different geographic areas that have been invaded and different combinations of D. siricidicola and S. noctilio genotypes vary in whether these nematodes sterilize female S. noctilio. Moreover, even in the event of sterilization, partial sterilization can occur, where not all woodwasp eggs are compromised. Sirex noctilio has now invaded North America accidentally, putatively accompanying D. siricidicola, but these host/parasite pairings do not result in female sterilization. More information is needed about the genetic diversity of D. siricidicola both where it is native and introduced. In addition, the host range of these nematodes is necessary to understand to evaluate their potential use in areas where pine communities are native. We collected and evaluated Deladenus parasitizing S. noctilio, S. juvencus, and associated insects in Hungary, Denmark, Spain, and Italy, as well as in the United States. Phylogenetic analyses were unable to fully provide fine resolution, although some community structure was evident. Many D. siricidicola samples from Hungary had identical COI and ITS sequences to the strain of D. siricidicola accidentally introduced to North America putatively when S. noctilio invaded. The same or similar strains of D. siricidicola parasitize two different Sirex species that utilize pines as well as a Sirex parasitoid and a pine-boring beetle, demonstrating some limited variability in host specificity of this species. These results highlight the genetic diversity of Deladenus siricidicola in its native range in Europe.

Growth of the Sirex-parasitic nematode Deladenus siricidicola on the white rot fungus Amylostereum.

The Kamona strain of the nematode Deladenus siricidicola has been extensively used as a biological control agent against invasive Sirex noctilio woodwasps in the Southern Hemisphere, where it sterilizes female hosts. 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. The mycophagous form feeds on Sirex fungal symbionts in the genus Amylostereum. The goal of this study was to compare reproduction of NS and Kamona D. siricidicola when feeding on four isolates of Amylostereum areolatum (three introduced and one native in North America) and one native strain of Amylostereum chailletii isolated from Sirex nigricornis. Mycophagous forms of the two D. siricidicola strains displayed relatively similar production of offspring when feeding on most of the A. areolatum 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.

Phylogenetic analysis of Deladenus nematodes parasitizing northeastern North American Sirex species.

The parasitic nematode Deladenus siricidicola is a biological control agent of the invasive woodwasp, Sirex noctilio. Since the discovery of S. noctilio in pine forests of northeastern North America in 2005, a biological control program involving the Kamona strain of D. siricidicola has been under consideration. However, North American pine forests have indigenous Sirex spp. and likely harbor a unique assemblage of associated nematodes. We assessed phylogenetic relationships among native Deladenus spp. in the northeastern United States and the Kamona strain of D. siricidicola. We sequenced three genes (mtCO1, LSU, and ITS) from nematodes extracted from parasitized Sirex spp. collected inside and outside of the range of S. noctilio. Our analyses suggest cospeciation between four North American Sirex spp. and their associated nematode parasites. Within two S. noctilio individuals we found nematodes that we hypothesize are normally associated with Sirex nigricornis. One individual of the native S. nigricornis contained Deladenus normally associated with S. noctilio. We discuss nematode-host fidelity in this system and the potential for non-target impacts of a biological control program using D. siricidicola against S. noctilio.

Susceptibility of the Adult Japanese Beetle, Popillia japonica to Entomopathogenic Nematodes.

To build upon prior research demonstrating the potential of entomopathogenic nematode dissemination by infected adult Japanese beetle, Popillia japonica, we evaluated susceptibility of the adult beetles to 20 strains of Steinernema and Heterorhabditis under laboratory conditions. The nematodes were applied at a rate of 10,000 infective juveniles per 10 adult beetles in 148 mL plastic cups containing autoclaved sand and sassafras leaves as a source of food for the beetles. All strains infected the beetles and caused 55% to 95% mortality. The most virulent strains that caused 50% beetle mortality in less than 5 days included a strain of H. georgiana (D61), three strains of Steinernema sp. (R54, R45, and FC48), and two strains of S. carpocapsae (All and D60). The ability of two strains of Steinernema sp. (R45 and R54) and two strains of Heterorhabditis bacteriophora (D98 and GPS11) to infect and reproduce in the beetle was further examined to assess the potential of infected beetles to disseminate nematodes upon their death. All four strains infected and killed the beetles, but only Steinernema strains reproduced in the cadavers. We conclude that both Heterorhabditis and Steinernema strains are able to cause mortality to adult Japanese beetle, but Steinernema strains may be effectively disseminated due to their reproduction in the beetle.