How long-term mass rearing affects the quality of the Trichogramma embryophagum (Hartig) (Hymenoptera: Trichogrammatidae) reared on Sitotroga cerealella (Olivier) eggs

Abstract

Background: Maintaining the quality and efficacy of biological control agents during long-term mass rearing plays a crucial role in the success of a biological control program. In this study, the biological traits of a local population colony of Trichogramma embryophagum (Hartig) with rearing on Sitotroga cerealella (Olivier) eggs for over 40 generations (G) were assessed. Results: Female adult longevity was significantly different among generations, ranging from 7.98 d in G5 to 5.19 d in G40. The reared wasps showed highest fecundity (60.50 eggs/female) in G5 compared to the other generations. The female sex ratio varied from 63.16% in G5 to 49.31% in G40. Significant differences were observed in population growth parameters and the highest gross reproductive rate (GRR) (40.96 eggs/individual) and net reproductive rate (R0) (38.21 eggs/individual) were found in G5. However, a non-significant difference was found in the intrinsic rate of natural increase (r) until the 10th generation, but its values significantly declined with increasing the generation numbers. The finite parasitism rate (ω) ranged from 0.468 host/parasitoid/day in G5 to 0.274 host/parasitoid/day in G40. Conclusions: The results showed that the quality of T. embryophagum reared under continuous laboratory conditions declined after 10 generations, and for use of them in biological control programs under field conditions, the reared population should be refreshed by adding wild individuals from time to time.