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Abstract
Lygus hesperus Knight is native to the western United States and is a perennial pest of numerous crops in California. It is responsible for triggering the early season application of insecticides on cotton, Gossypium hirsutum L., and strawberries, Fragaria L. Despite several surveys conducted in alfalfa (Medicago sativa L.) grown in central California, nymphal parasitoids associated with L. hesperus and L. elisus have not been found. Two exotic parasitoids were released into California beginning in 1998. Peristenus relictus (Ruhte), formerly P. stygicus Loan, and P. digoneutis Loan were collected from several locations in southern Europe and released at up to six locations over a 6-year period. At the original release site in Sacramento, a 0.25-ha plot of alfalfa, parasitism by P. digoneutis and P. relictus combined increased from zero to 90%, 3 years after the last releases were made. Parasitoids have been recovered from vacant fields of weedy annuals within 2 km of this site. Recoveries at more southerly release sites in central California have been poor.
Acknowledgments
We thank the following technicians that have contributed to this project: Claudia Erwin, Lea Ragaini, and Michelle Lawson. Dr Jay Bancroft (USDA ARS, Shafter, California) and Mr Mark Van Horn (UC Davis, Davis, California) helped in release of parasitoids and maintenance of sites. We are especially grateful to Jay Whistlecraft, of Agriculture and Agri-Food Canada for guidance on the rearing of Peristenus spp. Dr William Day provided useful suggestions by reviewing an earlier version of the manuscript. We are grateful to two anonymous reviewers for numerous constructive suggestions and corrections.