Evaluation for Potential Trichogramma (Hymenoptera: Trichogrammatidae) Strains for Control of the Striped Stem Borer (Lepidoptera: Crambidae) in the Greater Mekong Subregion

Trichogramma species and strains differ significantly in host specificity and performance. Nine Trichogramma strains, six of them collected from paddy fields in the Greater Mekong Subregion, were evaluated for performance on eggs of the striped stem borer, Chilo suppressalis (Walker), in both laboratory and field tests to determine potential Trichogramma strains that can be used in an inundative release in an integrated pest management program. In the laboratory glass vial tests, all strains showed higher parasitism rates on 0-24-h eggs than on the two older age groups (24-48 and 48-72 h). Wasp emergence rate was also higher from parasitized 0-24-h striped stem borer eggs, while Trichogramma immature duration was significantly prolonged on 0-24-h striped stem borer eggs. Parasitism rates differed among Trichogramma strains, with Trichogramma chilonis Ishii CJ strain showing significantly higher parasitism rate than any other strains. In the field tests, parasitism of sentinel striped stem borer eggs by Trichogramma strains released at 50,000, 100,000, and 200,000 wasps per hectare was low, with marginal yet significant differences between strains. The highest parasitism was achieved by T. chilonis CJ strain at the high and medium release rates. Hence, it can be concluded that T. chilonis CJ strain released at 100,000 wasps per hectare may be a cost-effective control tactic for field releases targeting striped stem borer.