Wildflowers provided nectar sources, but the influence on the wasp varied with the wildflower species and its seasonal availability. Wasps lived longer when fed on yellow rocket (Barbarea vulgaris) than on any of the other flowers tested. Two of the other plants, common lambsquarter (Chenopodium album) and perennial sowthistle (Sonchus arvensis), harbored bean aphids late in the season that provided honeydew for the wasps, also allowing longer wasp survival.

Food, from flower nectar or aphid honeydew, is essential for egg production. Wasps laid more eggs early in the season when fed on yellow rocket, but later wild mustard (Brassica kaber) was a better food source. Plants that provide refuge (shading) also helped the wasps. Manipulating the diversity and distribution of wildflowers in and around cabbage fields may increase the effectiveness of biological control of diamondback moth.

Source:

Idris, A. B. and E. Grafius. 1995. Wildflowers as nectar sources for Diadegma insulare (Hymenoptera: Ichneumonidae), a parasitoid of diamondback moth (Lepidoptera: Yponomeutidae). Environ. Entomol. 24: 1726-1735.