Abstract Macrocentrus iridescens French is a polyembryonic parasitoid with a wide host and geographic range in North America. In a survey of California pistachio orchards, M. iridescens was the most common parasitoid species reared from the obliquebanded leafroller, Choristoneura rosaceana Harris. To determine its potential as a biological control agent of the obliquebanded leafroller, we conducted laboratory studies and described M. iridescens immature development. We evaluated adult female longevity, brood size, sex ratio, and host stage preference for oviposition. The parasitoid egg develops polyembryonically. At 26.8°C, larval development required 25–30 d, and pupal development 10–12 d. There was a positive relationship between mandible size and development time, although individual stages could not be determined. Adult females survived on average 15.9, 1.6, and 0.9 d at 25°C when provided with honey and fructose solution, water only, or neither, respectively. Oviposition of fertilized eggs was observ...