Mating Behavior and Identification of Male-Produced Pheromone Components in Two Woodwasps, Sirex noctilio and Sirex nitobei, in China

SIMPLE SUMMARY: The woodwasp Sirex noctilio Fabricius is a major quarantine pest that was first discovered in China in 2013 and mainly harms Pinus sylvestris var. mongolica. Sirex nitobei Matsumura is native to China and closely related to S. noctilio. Recently, S. nitobei and S. noctilio were found to be attacking P. sylvestris var. mongolica from June to September successively in China. In recent years, pheromones have been useful tools for the development of pest evaluation and management strategies. Therefore, the aim of this study was to investigate the characteristics of two species of wood wasps (S. noctilio and S. nitobei): (1) mating behavior and circadian rhythms; (2) the factors influencing mating behavior; (3) the male-produced pheromone components in both species based on three reported components from S. noctilio. Finally, what we found was that most of the two species of wood wasps mated at two-days-old; within the same day, mating behavior peaks between 11:00 and 12:00; light conditions, individual size, and female–male proportion affect their mating behavior; (Z)-3-decenol became the main component of pheromone of both species. By investigating the mating behavior of two species of wood wasps and analyzing the pheromone production, we could proceed targeted control measurements during the mating period of wood wasps and provide strategic significance for the subsequent control. ABSTRACT: To protect vulnerable trees from native and invasive wood wasps, the mating behavior of these two woodwasp species (S. noctilio and S. nitobei, respectively) and factors influencing this behavior were investigated in cages outdoors. Male-produced pheromones were identified in both woodwasp species. Compared with the native species S. nitobei, the invasive species S. noctilio showed stronger mating ability, including mating frequency, time, and duration. The mating behavior of both species mainly occurred from 9:00 to 17:00 each day, peaking at 11:00 and 12:00. The daily mating behavior of both species was most directly related to light intensity. Both female and male S. noctilio and S. nitobei were capable of mating upon emergence, and most individuals mated at 2 days of age. For both species, a female-to-male ratio of 5:15 was most conducive to mating, and individuals with a larger body size were preferred as mates by males and females. (Z)-3-decenol was present in solid-phase microextraction extracts of both species. Two reported minor reference components, (Z)-4-decen-1-ol and (E, E)-2,4-decadienal, were not identified in either woodwasp species. The peak of male pheromone release occurred from 11:00–12:00 for 2-day-old individuals.