Abstract: 【Aim】 To study the oviposition behavior of Sirex noctilio, and to determine its oviposition capability, so as to provide a data basis for evaluating its reproductive potential and damage. 【Methods】 Logs of host Pinus sylvestris var. mongolica damaged by S. noctilio were collected from Xindian State Forest Farm of Duerbote Mongol Autonomous County,Daqing,HeilongjiangProvince,Northeast China. The oviposition behavior process and pattern of S. noctilio under the laboratory conditions were observed and analyzed. The oviposition holes of S. noctilio on P. sylvestris var. mongolica were dissected, and their structure characteristics were observed. 【Results】 The results revealed that S. noctilio wasps were sexually mature upon emergence, and they could mate and/or lay egg immediately. The ovipositing process of female adults of S. noctilio was divided into four stages: drilling into the bark, drilling into the xylem, laying egg (including injection of poisonous mucus and symbiotic fungi Amylosereum areolatum), and withdrawing the ovipositor. The most frequent oviposition time was between 360 to 540 s, accounting for 41.40% of the total frequency of various oviposition time. During these four stages, the time of drilling into the xylem was the longest, taking at least 90% of the total duration of oviposition. S. noctilio female adult would carry out 1-4 drillings once it confirmed a position. The oviposition time (t) showed a significantly positive correlation with the number of oviposition cycles: 1 cycle when t<360 s; 2 cycles when 360 s≤t<540 s; 3 cycles when 540 s≤t<780 s; and 4 or more cycles when t≥780 s. The proportions of 1, 2, 3 and 4 cycles of oviposition at one oviposition hole were 21.66%, 41.40%, 27.39% and 9.55%, respectively. 【Conclusion】 The number of oviposition cycles of female adults of S. noctilio is positively correlated to its oviposition time. Based on this relationship, the number of oviposition cycles can be inferred once the oviposition time is investigated. The more the oviposition cycles of S. noctilio, the higher the risk of its harm to P. sylvestris var. mongolica.

Key words: Sirex noctilio, bionomics; Pinus sylvestris var. mongolica, oviposition behavior, symbiotic fungi, trunk borer