Abstract:
The woodwasp, Sirex noctilio, in association with its mutualistic fungus, Amylostereum areolatum, pose a threat to forest plantations in the Southern Hemisphere. This invasive pest insect is controlled with a biological control agent, a parasitic nematode, Deladenus siricidicola. This biological control method has previously been successful in controlling S. noctilio populations, achieving over 90% parasitism. Recent studies have shown that there is a variability in the efficiency of the nematode and there are some S. noctilio populations that are resistant to certain nematode strains. A better understanding of the immune response of the wasp during its interaction with the nematode has relevance to the evolution of immune response pathways in Hymenoptera in general and may also assist in the selection of more virulent/effective nematode strains in the future. The molecular mechanisms underlying the interaction between S. noctilio and D. siricidicola are, however, unknown. In this study, we aimed to identify the immune-related genes of this wasp. To enhance our findings, we used transcriptome analysis on immune challenged and unchallenged S. noctilio larvae to identify additional components implicated in immune reactions. A total of 180 immune-related genes were identified through the comparison of the S. noctilio genome with the genes and genomes of other Hymenoptera. Key elements of the conserved Toll, IMD, JNK and JAK-STAT signalling pathways were identified in the S. noctilio genome. Differential gene expression analyses performed on infected S. noctilio larvae demonstrated that typical wounding response mechanisms are activated by this insect in response to all the treatments. This study provides insight into the molecular pathways of innate immune processes in S. noctilio larvae and will serve as the foundation of future studies on the interaction between the woodwasp and pathogens/parasites.
