Monitoring of Mutual Interference Behavior of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) over 45 Generations of Rearing on Angoumois Grain Moth.

Trichogramma brassicae (Bezdenko) is one of the most common species of natural enemies used in augmentative biological control programs in many countries. Understanding of the foraging behavior of a parasitoid can help us to improve its performance under field conditions. This study is the first assessment of trends in mutual interference behavior of T. brassicae under long-term mass rearing (over 45 generations) on a common factitious host, Sitotroga cerealella (Olivier). Our results revealed that the total parasitism rate of T. brassicae reared on S. cerealella eggs was significantly affected by parasitoid densities and number of generations under continuous rearing. Also, parasitoid density and number of generations in rearing had significant effects on the per capita parasitism rate. Meanwhile, per capita searching efficiencies were different in sequential generations and at different densities. The number of hosts parasitized per parasitoid decreased on day 1 of the experiment with increasing parasitoid density, showing the effect of mutual interference. The linear regression between the natural logarithm of per capita searching efficiency and the natural logarithm of parasitoid density showed an inverse relationship. While the m (interference coefficient) values increased, the Q (quest constant) values had a decreasing trend over 45 generations. The highest (- 0.167) and lowest (- 0.242) values of m were observed in G45 and G5, respectively. Accordingly, G5 and G45 had the highest (0.053) and lowest (0.023) Q values, respectively. Thus, it seems the negative effects of mutual interference decreased over generations.

Quality control of the parasitoid wasp Trichogramma brassicae (Hymenoptera: Trichogrammatidae) over 45 generations of rearing on Sitotroga cerealella.

Trichogramma brassicae (Bezdenko) is an important biological control agent that has been used widely against many lepidopteran pests. Commonly, colonies of Trichogramma are mass reared on factitious hosts such as Sitotroga cerealella (Olivier) over many generations. In this study, we evaluated the quality and performance of a colony of T. brassicae that had been reared for over 45 generations (G) using two-sex life table parameters and parasitism capacity. We found that female adult longevity was significantly different among sequential generations, ranging from 5.58 ± 2.5 d (at G5) to 3.75 ± 1.42 d (at G45). However, no significant difference was found in male adult longevity among different generations. Although female wasps survived longer until the 15th generation, they allocated more days for egg laying at G5 and G10. The highest values of gross reproductive rate (GRR), net reproductive rate (R0 ), intrinsic rate of increase (r), finite rate of increase (λ) and mean generation time (T) were found in G5 and G10, which also showed significantly higher c0 . No significant difference in the finite parasitism rate (ω) was found among generations up to G15. These results suggest that T. brassicae wasps held under continuous laboratory rearing can be used successfully in biological control programs until the 15th generation without any loss of quality or performance. However, laboratory mass rearing colonies declined in quality after 15 generations and we suggest that they should be rejuvenated regularly by adding field-collected parasitoids periodically.