In Denmark, the most important Hypera species are the lesser clover leaf weevil Hypera nigrirostris (Fabricius) and clover head weevil Hypera meles (Fabricius). This project documents that both species are parasitized by the parasitoid Bathyplectes curculionis (Thomson), parasitizing the young weevil larvae in the clover heads.
The current project studied if the parasitoid can be conserved and isolated from harvested white clover crops and hereafter be used to regulate Hypera weevils in consecutive clover crops. The prerequisites would, thus, be 1) that the cocoons can be separated from the harvested raw material, 2) that the cocoons can be stored throughout the winter season, 3) that the cocoons can be released in the new clover seed field, 4) that adequate numbers of the adult parasitoid can hatch at the right time related to the development of the weevil larvae and 5) that the released parasitoids reduce the damage by the weevil within the year of release or reduce the number of weevils hatching, which constitutes the weevil population in the following year.
The results revealed that the number of intact and pollinated florets was significantly positively influenced by the number of parasitoids and increased from 60% to 85-85% in both years with an increase in the number of released parasitoids.
The number of clover head weevils hatching from the white clover flower heads, which would constitute the following year’s population was, however, not affected by the number of parasitoids released.
The results from the project show that the parasitoid B. curculionis of the clover head weevil has the potential of being part of a future strategy to increase the seed yield and reducing the application of insecticides in white clover seed production.