Sustained releases of the pupal parasitoid Spalangia cameroni (Hymenoptera: Pteromalidae) for control of house flies, Musca domestica and stable flies Stomoxys calcitrans (Diptera: Muscidae) on dairy farms in Denmark

Releases of Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) were conducted every second week from mid-April and up to October 2001, on four organic dairy cattle farms in Denmark to test the efficacy of this wasp as a biological control agent against house flies and stable flies. Season-long parasitism of sentinel house fly pupae averaged 32.7 and 35.8%, in two release farms versus 8.4 and 9.8%, in two control farms. Compared with the controls, the mean density of house flies and stable flies per animal was distinctly suppressed due to S. cameroni releases in the period August–September of normal peak abundance of flies. A positive correlation between temperature and parasitism was found; suggesting that temperature partially explains the discrepancy observed between an apparent suppression of flies and a relatively low overall percentage of parasitism. Expressed as a percentage of the total number of adult parasitoids recovered from the four dairies, S. cameroni was most abundant (80.5–93.1%). From early summer and onwards Muscidifurax raptor Girault and Sanders (4.0–6.0%) occurred frequently along with Spalangia nigripes Curtis (0.8–8.5%), Pachycrepoideus vindemiae (Rondani) (<5.0%), and Phygadeuon fumator Gravenhorst (Hymenoptera: Ichneumonidae) (0.3–6.9%). Based on the results, the cost of fly control achieved using S. cameroni and the future prospects for biological control of flies, are discussed.