Background Western conifer seed bug, Leptoglossus occidentalis Heidemann (Hemiptera: Coreidae), is an invasive polyphagous pest of coniferous trees. It causes serious economic losses in pine kernel production. Biocontrol of L. occidentalis through the egg parasitoid Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae) seems to be sustainable solution to reduce economic losses of the pest. In this study, the biology of O. pityocampae was investigated on its natural host, L. occidentalis, under laboratory conditions. Results In this context, the effects of host age, female age, and temperature on parasitism rate, emergence rate, developmental time, and longevity were investigated. Female age had a great influence on the parasitism rate. Parasitism rates were 8.0, 17.0, and 37.3% in 1-, 3-, and 5-day-old females, respectively. There was no effect of host age or female age on emergence rates at the two different temperatures (25 and 30 °C). Emergence rate ranged from 74.0 to 88.3%. The longest developmental time (17.9 d) was obtained on 3-day-old hosts at 25 °C. The longevity, which was one of the important criteria of the parasitoid, was significantly affected by temperature. Conclusion The results of this study on the biology of O. pityocampae may contribute significantly to the biological control studies of L. occidentalis. This egg parasitoid can be mass-produced on lepidopteran hosts for field releases against L. occidentalis.