Vegetable Crops News

Flowers Affect Diamondback Moth Parasitoid

The small wasp Diadegma insulare is one of the most important parasitoids of diamondback moth in North America, commonly causing 50% or more mortality of caterpillars on unsprayed plants. The effects of several wildflowers on the longevity and fecundity of this wasp were studied in Michigan.

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.

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