Nasonia vitripennis are a parasitic wasp which have been used frequently for studies of spontaneous and induced mutations. They have a relatively short generation time of approximately 15-30 days depending on the incubation temperature. The females are diploid and will produce haploid males if they do not mate but diploid females if they do. The females lay the eggs in blowfly (Sarcophaga bullata) pupae, where the wasp larvae can grow in a rich environment. Many mutants have been cultivated into sustainable stocks. These mutants include eye-color (normally reddish brown to dark brown in color), body color (normally a greenish-yellow color) as well as body mutations which affect wings, legs or body shape. See below for a list of stocks currently at Middlebury College. Many of the color mutants are temperature dependant. They become darker or lighter due to the temperature at which they are raised. The wasps also have an alternative life cycle when the temperatures drop substantially. When subjected to cold temperatures, the wasps will go into diapause, a stage at which they are more resistant to the cold temperatures, and will not fully develop until exposed to 3 or more months of cold temperatures and then normal temperatures (15-25C). The diapause larvae can be stored for up to a year at just above freezing.