Does host age affect progeny production and progeny fitness in Trichopria sp.?

The gregarious endoparasitoid Trichopria sp. (Hymenoptera: Diapriidae) is currently under evaluation for its potential to suppress the levels of parasitism in larvae of the silkworm Bombyx mori (Lepidoptera: Bombycidae) caused by the tachinid fly Exorista bombycis (Louis) (Diptera: Tachinidae) in the rearing houses of sericulture farmers in southern India. Parasitism by E. bombycis currently results in cocoon yield reductions of 10–20 %. Prior to the mass production and release of Trichopria sp., there is a need to understand the factors that affect progeny production and fitness. Within this framework, we have attempted to determine whether host age has an impact on the numbers of Trichopria sp. progeny produced and on the subsequent fitness of the adults of the wasp. Two day-old adult females of the parasitoid were allowed to parasitize day (D) 1, 3, 5, 7, and 9 puparia of E. bombycis at a ratio of 1:4 (wasp:host). After eclosion of the parasitoid adults, data on the rate of parasitism, developmental period, brood allocation, progeny production, sex ratio, female progeny longevity and adult size were recorded. The reproductive performance of the adult progeny was also recorded by allowing them to parasitize three day-old E. bombycis puparia. Host age was seen to have an effect on several of the parameters recorded, such that while the most progeny were produced by the youngest (D1) hosts, larger wasps emerged from older E. bombycis puparia. It was, however, apparent that all but the oldest hosts (D9) examined were able to support adequate parasitoid development. Further, only relatively minor impacts on progeny fitness were observed between wasps deriving from hosts of different ages. However, the results strongly indicate that optimal production and parasitoid performance will be obtained by using young hosts of less than three days old.