Effects of exposure time and ratio of irradiated larvae from three medfly strains on progeny yield in Diachasmimorpha longicaudata (Hymenoptera: Braconidae) mass rearing

An augmentative biological control strategy against Ceratitis capitata (= medfly) in fruit-producing irrigated-valleys of San Juan, central-western Argentina, has been recently implemented by the San Juan Fruit Fly Control and Eradication Program. The Asian-native parasitoid Diachasmimorpha longicaudata is currently reared at the San Juan Medfly and Parasitoids Mass Rearing Facility for this purpose. In this regard, the objective of this study was to evaluate adult emergence and offspring sex ratio to improve parasitoid production. Three medfly strains at different host larvae densities and exposure times to female parasitoids were assessed. Prevalence of superparasitism was also considered. Three parasitoid population lines were used in the trials: one reared on medfly larvae of the Vienna-8 temperature-sensitive lethal (tsl) genetic sexing strain without inversion, and the other two on larvae of biparental medfly strains native to San Juan (central-western Argentina) and Tucumán (northwestern Argentina). Gamma-irradiated 6 d-old larvae (early third-instars) of each medfly strain were exposed to parasitoids for 30, 60, 90, and 120 min at 3:1, 6:1, and 9:1 host/parasitoid ratios. The Vienna-8 C. capitata strain was as efficient in producing parasitoids as both biparental native strains. Medfly larvae exposed to 10 female parasitoids for a relatively long time (1.30 hrs) at a high ratio (6–9:1) of host to parasitoid were enough to achieve the highest mean adult emergence (50–60%) and a female-biased offspring sex ratio. Superparasitism positively influenced female parasitoid production. These findings may be used to develop a more cost-effective mass rearing method for D. longicaudata.