Improving mass rearing systems for micro-hymenoptera: Case studies with Diaeretiella rapae and Encarsia tricolor

Abstract: The improvement of the quality of rearing systems can enhance the efficiency of biological control agents. Diaeretiella rapae M´Intosh (Hymenoptera: Aphidiidae) and Encarsia tricolor Förster (Hymenoptera: Aphelinidae) are present on crops under open field conditions but their efficiency is not enough to maintain pests below the economic injury level. In order to improve the quality of the rearing systems of both parasitoids, we evaluated the effect of three host plants: Broccoli var. Marathon F1, Brussels sprouts var. Hilds Ideal and Cauliflower var. Freemont; two architectures of the plant: with and without pruning and two sizes of cages: 0.21 m3 and 0.023 m3. The production of mummies per plant and longevity of the parasitoids were measured among other variables. In the first experiment, the number of mummies of D. rapae and E. tricolor were significantly higher on broccoli as host plant as compared to other treatments by 169% and 138%, respectively. In the second experiment, the number of mummies of D. rapae and E. tricolor were higher in the treatment with pruning as compared to the control by 41.63% and 95%, respectively. Pruning also increased longevity of D. rapae and E. tricolor by 55% and 200%, respectively. In the last experiments, the number of mummies of D. rapae and E. tricolor were an 18.5% and 40.7%, respectively higher in the large cages than in the small ones. Additionally, large cages increased longevity of E. tricolor by 51.6%. The selected treatments also had positive effect in other quality criteria, such as: herbivore size, lifespan of banker plants, reduction of incidence of powdery mildew and adaptation in field. In conclusion, the use of pruned broccoli plants, in large cages substantially improved the quality of both rearing systems.