The biology of Megastimus wachtli Seitner (Hymenoptera: Torymidae) was found to be similar to other species of Megastigmus. During the period of flight that lasted six weeks from the beginning of September to mid-October, M. wachtli laid eggs in cypress (Cupressus sempervirens L., Pinales: Cupressaceae) cones and showed preferences for oviposition on particular sites on cones. M. wachtli has a high potential for colonization because it has evolutionary advantages due to its developmental possibilities including its capacity for parthenogenesis, its fecundity and longevity. It generally did not attack cones colonized by the torticid moth, Pseudococcyx tessulatana (Lepidoptera: Tortricidae). The competition between these species for use of cypress cones suggests that they use different strategies for different species of cypress. The number of insects that could develop relative to the number of cones available also varies between species of cypress.