Intraspecific hybridization and the recovery of fitness in the biocontrol agent Trichogramma galloi (Hymenoptera: Trichogrammatidae)

Hybridization is an important evolutionary mechanism that can affect the fitness of populations. Intraspecific hybridization may be a relevant method to enhance biological control agents’ fitness because is expected to promote hybrid vigor and increase genetic variance for relevant phenotypic traits. Alternatively, another effect of intraspecific hybridization is outbreeding depression which can lead to reduced fitness. We investigated these questions by reciprocally crossing three populations of the parasitoid wasp Trichogramma galloi, a biocontrol agent of the sugarcane borer, Diatraea saccharalis. The number of crosses producing viable daughters was not affected by the mating type. Homotypic crosses produced 94% of viable daughters while heterotypic crosses 92%. The I_PSI and IA_PSI values, used here to detect sexual isolation and asymmetric mating compatibilities, respectively, were not significant, showing that there were neither mating incompatibilities nor reproductive barriers between populations. However, we observed a low fitness value (W, cross-product estimator) for females from one of the populations, which combined with its low fecundity supports the hypothesis that the population suffers from inbreeding depression. Our results also provide evidence of the recovery of fitness in hybrids (F1) obtained from this population, which was observed comparing fecundity between the parental population (19.76 ± 4.02 parasitized hosts) with one of the associated hybrids (30.27 ± 3.88 parasitized hosts). The performance of other hybrids relative to the best parent did not suggest heterosis. The admixture between populations may be a useful tool to improve the performance of captive populations that are suffering from inbreeding depression; however pilot tests should be conducted to find the most suitable populations to cross.