Evaluation of Trichogramma spp. (Hymenoptera: Trichogrammatidae) Against Two Pyralid Stemborers of Texas Sugarcane

The role of Trichogramma minutum Riley (reared on Helicoverpa zea [Boddie] eggs or on an artificial diet) and T. pretiosum Riley (reared on H. zea eggs) as parasitoids of the Mexican rice borer, Eoreuma loftini (Dyar) and sugarcane borer, Diatraea saccharalis (F.), was assessed under laboratory and greenhouse conditions. The laboratory results showed that T. minutum reared on H. zea eggs parasitized 52.5% of Mexican rice borer eggs, compared to 50.3% for T. pretiosum. Parasitization of Mexican rice borer eggs by T. minutum reared on the artificial diet (62.6%) was not significantly different compared to those reared on H. zea eggs (52.5%). Trichogramma minutum reared on H. zea eggs parasitized 42.0% of sugarcane borer eggs, compared to only 12.6% by T. pretiosum. About 43.4% of sugarcane borer eggs were desiccated, despite 80 to 85% RH. Percentages of emergence (83.0%), female progeny (67.0%), deformed females (3.3%), and development time (8.2 d) in T. pretiosum reared from Mexican rice borer eggs did not differ significantly from those reared on H. zea eggs (91.3%, 72.5%, 2.5%, 8.3 d, respectively). However, T. pretiosum females reared from Mexican rice borer had greater longevity (2.5 d) and body length (0.385 mm) than females reared on H. zea (1.6 d, 0.326 mm, respectively). In the greenhouse, T. pretiosum parasitized an average of 55.3% of the Mexican rice borer eggs (egg masses were distributed on the sugarcane plants). About 21.0% of the eggs were dessicated, probably due to puncturing by the parasitoid, compared with 4.5% in the control, where egg masses were distributed on the plants without release of Trichogramma. Our results show the potential for use of Trichogramma spp. to control sugarcane stalk borers in a field IPM program.