Survey of natural enemies of Sirex noctilio (Hymenoptera: Siricidae) and biology of the dominant parasitoids in China.
[Objective] In this study, the natural enemies of the invasive pest Sirex noctilio (Hymenoptera: Siricidae) in China were identified, and the dominant parasitoids and their biology were determined to provide a basis for determining the optimal control period and biological control agents. [Method] The sampling sites were set in the Scotch pine stands infested by Sirex noctilio, and continuous field surveys were conducted in combined with laboratory rearing and observation in this study from 2015 to 2016. [Result] (1) The result showed that there were 3 types of natural enemies in Sirex noctilio, including parasitic wasps, pathogenic fungi and nematode. Of which there were 5 species of parasitic wasps: Rhyssa persuasoria persuasoria (Hymenoptera: Ichneumonidae), Ibalia leucospoides leucospoides (Hochenwarth), Ibalia rufipes drewseni Borries (Hymenoptera: Ibaliidae) and Pseudorhyssa nigricornis (Ratzeburg) (Hymenoptera: Ichneumonidae), 2 species of pathogenic fungi (Trichoderma atroviride Bissett and Trichoderma viride Persoon) and a nematode Deladenus siricidicola Bedding. (2) Rhyssa persuasoria persuasoria was determined as a dominant species of parasitoid, and its natural parasitism rate was 9.3%. The wasp had one generation a year, ovipositing in young larvae or older instar larvae of its host. It was primary monoparasites and overwintered as larvae within tunnels of Sirex noctilio. Its pupal stage was 10-15 d and the peak period of the adult emergence was in the early May. The adult had a longer life span. It had a strong ability of rainwash resistance and a good adaptability to natural environment. (3) Through anatomical observation of Sirex noctilio under the microscope, the infection rate of larvae of Sirex noctilio caused by nematode was 32.1%, and the infection rate of the adult was up to 70.9%.[Conclusion]The above-mentioned result showed that Rhyssa persuasoria persuasoria (L). was an important insect species of natural enemies for control Sirex noctilio and the most appropriate control period was larvae or older instar larvae (i. e. from late April to middle May in local time). Moreover, based on the parasitism rate and effect, D. siricidicola Bedding would be considered the primary biological control means, which should further focus on the study and utilization in biological control of the pest.