Sirex noctilio F. is a woodwasp that develops within stressed and dying pine trees, Pinus spp. It is native to Eurasia and North Africa but has spread to other continents and has become a pest of pine plantations in the Southern Hemisphere. In nature, adults live for <2 wk, during which time males form leks. We investigated environmental and biological conditions related to mating of these woodwasps. We hypothesized that temperature, light, and size ratio of the sexes (male:female) influence mating receptivity. A total of 71 12-min mating trials, with 10males and 1 female in each trial, were conducted in outdoor cages. As a precursor to mating, a male would approach a female from behind and touch her with his antennae and, if the female was receptive, mating proceeded. Sirex noctilio mated more often at higher temperatures, but the size ratio of sexes and degree of cloud cover did not influence female receptivity tomating. Females that mated oftenmated multiple times (2.6 ± 0.2, mean ± SE; range 1–7), and numbers ofmatings increased with increasing temperature and was greatest during the last 4-min of the 12-min trials.