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item Hoelmer, Kim

Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings
Publication Acceptance Date: 4/29/2005
Publication Date: 9/12/2005
Citation: Pickett, C.H., Coutinot, D., Hoelmer, K.A., Kuhlmann, U. 2005. Establishment of Peristenus spp. in northern California for the control of Lygus spp. 2nd International Symposium on Biological Control of Arthropods, p. 116-125.

Interpretive Summary: Lygus bugs (tarnished plant bugs, TPB) are important insect pests of numerous crops in North America. They also occur in Europe and Asia where they are not generally regarded as significant pests, in part due to effective natural enemies. In the western U.S., native natural enemies of lygus are not effective in limiting pest populations. Previous attempts several decades ago to introduce new, more effective, natural enemies from Europe were unsuccessful. However, the establishment of a European parasitic wasp species against TPB in the northeastern U.S. a few years ago resulted in new interest in biocontrol of TPB in other regions of North America. To reduce populations of western TPB, parasitic wasps attacking TPB in select areas of southern Europe with climates very similar to California were collected and introduced into California, where they have now become established.

Technical Abstract: Lygus hesperus is native to the western United States and is a pest of numerous field and seed crops. In California, it is a key pest of cotton and strawberries, both highly valued crops. Extensive surveys for natural enemies in the western United States documented only low levels of parasitism of Lygus species (primarily L. hesperus) in alfalfa, especially by nymphal parasitoids. Beginning in the early 1970's the USDA ARS initiated importation of parasitoids associated with Lygus rugulipennis infesting alfalfa in central Europe and Turkey. These previous attempts failed to establish Peristenus stygicus during the mid 70's in the southwestern U.S., including the San Joaquin Valley in central California. Importation of nymphal parasitoids into the eastern United States during the 1980's, however, successfully established a European Peristenus species that has since reduced numbers of Lygus lineolaris, a close relative of L. hesperus, infesting alfalfa. Recently, additional populations of parasitoids were collected from southern France, central Italy and Spain by CABI Bioscience and the European Biological Control Laboratory, USDA ARS. These populations of Peristenus stygicus and Peristenus digoneutis were released in Sacramento in alfalfa managed by CDFA beginning in 1999. Parasitoids were also released at several other sites in inland valley and coastal central California. Parasitism has increased each year at the original release site in alfalfa in Sacramento. Three years following the last releases there, we continue to find abundant numbers of both P. stygicus and P. digoneutis. Maximum summer parasitism has increased each year since releases were made, reaching 90% in summer 2004. Parasitized nymphs of L. hesperus have been collected from nearby vacant lots infested with black mustard and wild radish. These results indicate that these parasitoids are permanently established in the Sacramento region. Over the same period of time, maximum Lygus counts varied from 3 to 14 per sweep, and appear to be declining. In contrast to results at the first release site in Sacramento, parasitism at other inland valley release sites has yet to increase, despite additional releases in 2002 and 2003. However, at one of the central coast sites we recovered parasitoids, as larvae, at a control site 300 m from where they were first released 6 weeks earlier. Only the introduced parasitoids Peristenus stygicus and P. digoneutis were recovered, i.e. no native braconids. Native parasitoids, Peristenus 'near' howardi, have been recovered from another mirid, Closterotomus norvegicus, at the same locations.