Effects of host age and radiation dose in Diachasmimorpha longicaudata (Hymenoptera: Braconidae) mass-reared on medfly larvae of the tsl Vienna 8 genetic sexing strain

Augmentative release of parasitoids against Ceratitis capitata (Weidemann) is currently at an early stage in Argentina. The success of this environment-friendly strategy depends on suitable mass-rearing procedures. The integration of radiation in the rearing process improves both mass production and handling of fruit fly parasitoids. Diachasmimorpha longicaudata (Ashmead) is reared on larvae of tsl Vienna-8 C. capitata strain at the BioPlanta San Juan, Argentina. The aim of the current study was to identify the best combination of larval host age, exposure time, and host gamma-radiation dose to achieve the greatest parasitoid mass yield with the highest female-biased offspring ratio. The effect of host radiation doses on parasitoid fitness-related parameters from the first filial generation was also assessed. Firstly, host larvae aged 5-7 d-old were exposed to parasitoids for 30, 60, 90, 120, 150 and 180 min at a constant 4:1 host/parasitoid ratio. The most productive exposure procedure was 5-6 d-old larvae for 1.30 h. Secondly, batches of 180,000 naked host larvae aged 5-6 d-old were irradiated at 0, 60, 65, 70, 75, 80, 85, 90, 95, and 100 Gy. Suitable radiation doses for wholly suppressing host emergence were at 85-100 Gy. Thirdly, 5-6 d-old host larvae irradiated at 85, 90, 95, and 100 Gy were exposed to parasitoids. 6 d-old larva irradiated at 90 Gy was the most suitable combination to achieve the highest parasitoid emergence and female offspring values. Increasing radiation doses beyond 90 Gy did not significantly enhance parasitoid yield and did not improve female-biased offspring ratio. Fourthly, survival, fecundity, sex ratio, development time and parasitoid offspring size were not adversely affected by radiation. Gross fecundity and net reproductive rates, and sex ratio remarkably improved in comparison to that recorded on parasitoids reared on non-irradiated larvae. These findings greatly encourage the use of augmentative biological control against medfly in Argentina.