In the late 1950's the United States
Department of Agriculture began introducing several species of
parasitoids from Europe (the native range of the alfalfa weevil).
These parasitoids, along with a naturally occurring fungus, now
keep the alfalfa weevil under biological control in the northeastern
U. S. However, alfalfa weevil persists as a major pest in Virginia,
especially in the Piedmont region. Some of the key parasitoids contributing to the biological control of alfalfa weevil are:
Microctonus aethiopoides: This is one of the primary parasitoid species of alfalfa weevil adults. Weevils that are parasitized by M. aethiopoides become sterile. Samples of alfalfa weevil adults collected in Virginia from 1998 to 1999 revealed a low parasitism rate. One possible reason for the relatively low level of M. aethiopoides parasitism in Virginia is that the parasite never truly got established in the state.
Microctonus aethiopoides (University of Wisconsin)
Bathyplectes species: Several species of Bathyplectes wasps attack alfalfa weevil larvae. In the eastern U. S., B. anurus is the dominant species.
More on Bathyplectes species (University of Wisconsin)
Fungal pathogens: An entomopathogenic fungus, Zoopthora phytonomi, is the most important pathogen of alfalfa weevil larvae. This fungus can cause up to 90% mortality of larvae when environmental conditions are suitable.
Alfalfa Weevil Control by the fungal pathogen Z. phytonomi in Oklahoma (University of Wisconsin)