Potential use of the egg parasitoid Trichogramma pretiosum in the management of Rachiplusia nu.

Abstract

Outbreaks of Rachiplusia nu have occurred on soybean in Brazil as the first species resistant to the Bt soybean expressing only Cry1Ac protein, triggering a significant increase in insecticide use on the crop. This threatens one of the most important benefits of adopting Bt soybean cultivars - the reduction of chemicals. Therefore, this research studied the biology and parasitism capacity of Trichogramma pretiosum at 20, 25, and 30 ± 2 °C on R. nu eggs in order to evaluate the potential of releasing this egg parasitoid in soybean to manage R. nu. Parasitoid exhibited high biological performance on the R. nu eggs as observed in the lifetime parasitism of 24.9, 46.4, and 34.4 R. nu eggs at 20, 25, and 30 °C, respectively, and 100% emergence in both biology and parasitism capacity experiments. The sex ratio was statistically lower at 20 °C (0.4947), but at all studied temperatures, the production of female descendants was equal (sex ratio of 0.4947 at 20 °C) or higher (sex ratio of 0.6666 at 25 °C and 0.6524 at 30 °C). All other evaluated parameters were similar to previously positive recorded observations for T. pretiosum on other soybean pests, such as Anticarsia gemmatalis and Chrysodeixis includens, against which the parasitoid has already been commercially released in the fields as a biocontrol option. Therefore, T. pretiosum might also be released in soybean as an egg parasitoid against R. nu, what needs to be confirmed in future field trials.