Local and landscape effects on parasitism of alfalfa weevil by a specialist parasitoid wasp

Background/Question/Methods

Intensification of cropland has lowered habitat diversity in agricultural landscapes leading to fewer resources for natural enemies of agricultural pests. Alternative habitats can provide refuge from management disturbances, additional food sources, and overwintering habitat important for many types of natural enemies. Bathyplectes curculionis is a specialist parasitoid wasp of the alfalfa weevil (Hypera postica), a major pest of alfalfa throughout the intermountain west. B. curculionis was first introduced to the region in the early 20^th century. Despite these efforts, alfalfa weevil continues to be a problematic pest in the region. The aim of this study is to determine if B. curculionisare still present in southeastern Wyoming, and if so, what landscape scale patterns may predict parasitism rates. In spring of 2014, 10 alfalfa fields in southeastern WY were swept for alfalfa weevil larvae. Larvae were reared to adulthood to determine percent parasitism.

Results/Conclusions

Parasitoid wasp B. curculionis occurred in all sampled fields, with parasitism rates of alfalfa weevil ranging from 7% to 34% across fields. This high variability from field to field is consistent with previous work on B. curculionis in the region.  Similar parasitism rates were grouped spatially, with like rates occurring closely together. We found a negative relationship between parasitism and weevil abundance. These results confirm that B. curculionis have persisted in the area, but at levels too low and variable to provide biological control of alfalfa weevil. Future research will expand the number of field sites sampled and characterize the landscape around field sites to determine effects of landscape composition and configuration.