Parasitism and sex ratio of Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) against Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) on cruciferous cultivars under different temperatures

Background Diadegma insulare (Cresson) is the most efficient parasitoid of Plutella xylostella (L.) in cruciferous crops. Considering its effectiveness, the present study was performed to investigate the impacts of cauliflower and cabbage cultivars under 3 different temperature regimes on the parasitism efficiency and offspring sex ratio of D. insulare. Main body This study revealed that D. insulare remained active at all the 3 temperatures (i.e., 19, 23, and 27 °C) and on all selected cruciferous cultivars. However, 23 °C (along with 65±5% RH and 16L: 8D hours) was the most suitable temperature, whereas relatively preferred host plant cultivars were the “White marble” (cauliflower) and “Asha” (cabbage) at which comparatively higher parasitism rates (79.39 and 73.31%, respectively) were recorded. Moreover, non-significant differences were observed in the offspring sex ratios of the parasitoid at different temperature regimes; however, minute differences were found among studied cruciferous cultivars. Conclusion Overall, “White marble” (cauliflower) and “Asha” (cabbage) were recommended to be used as potential host plant cultivars for mass rearing of D. insulare.

War of the wasps: is Diadegma insulare or Microplitis plutellae a more effective parasitoid of the Diamondback Moth, Plutella xylostella?

Parasitism levels by Diadegma insulare (Muesebeck) (Hymenoptera: Ichneumonidae) and Microplitis plutellae (Haliday) (Hymenoptera: Braconidae) at various densities of their host, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were assessed. Cages with densities of 10 hosts, 20 hosts, and 40 hosts were set up, with the cage volume (40 500 cm3) and number of wasps (2 females) remaining constant. The host populations were also exposed to the wasps for two different exposure times: 1 day and 3 days. The study showed that D. insulare was a better parasitoid overall, achieving a level of parasitism equal to or higher than M. plutellae at all densities. Microplitis plutellae performed best at a lower host density (76% ± 9% of 10 hosts vs. 43% ± 3% of 40 hosts). Diadegma insulare performed similarly at all densities tested (75% ± 5% of 10 hosts, 83% ± 4% of 20 hosts, and 79% ± 6% of 40 hosts). This suggests that D. insulare may be the better parasitoid overall and should be applied in severe, large-scale infestations, while M. plutellae may be better for small-scale infestations.