Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2005
Publication Date: 12/10/2005
Citation: Seymour, L.M., Mowrey, T.M., Day, W.H., Barbour, J.D. 2005. Parasitism of Lygus spp. nymphs by the Parasitoid wasp Peristenus howardi in the alfalfa seed-growing region of the Pacific Northwest. Journal of Insect Science. 5(44):1-8. Interpretive Summary: A new species of wasp, apparently native, was previously discovered parasitizing the western tarnished plant bug (WTPB) in Idaho by USDA and University of Idaho scientists. The WTPB is a very important pest insect that damages cotton, seed crops, fruits, vegetables, and seedlings. This research extended our knowledge by measuring the effectiveness of the parasite, P. howardi, on crops and weeds on farms in SW Idaho and adjacent Oregon. Parasitism of WTPB in seed alfalfa at Parma, Idaho research station was 66% (2002) and 81% (2003), which should provide a practical reduction in this pest. However, parasitism was considerably lower in other crops, at other locations, and in most weeds, indicating that further research will be required to determine why parasitism varies, and whether a commercially–practical biological control system (that would reduce insecticide costs to farmers) can be devised. DNA tests indicated that about 20% of parasites were not P. howardi, so a second new species may be present.
Technical Abstract: Peristenus howardi Shaw (Hymenoptera: Braconidae) has been found to parasitize a large proportion of Lygus species in some Washington and Idaho alfalfa seed fields. During 20022003 we conducted a survey to estimate the proportion parasitism of Lygus spp. and the amount of that parasitism attributable to P. howardi in crop and non-crop plants attacked by Lygus spp. in the alfalfa seed growing region of southwestern Idaho and eastern Oregon. Percentage parasitism was estimated from dissection of field-collected Lygus spp. nymphs. We used polymerase chain reaction (PCR) of DNA extracted from parasitoid larvae followed by restriction endonuclease digestion of PCR products to distinguish P. howardi from other potentially co-occurring Peristenus species. Peak parasitism of Lygus nymphs occurred between the first and third weeks of July for both years for all host plants sampled. Of the parasitoid larvae recovered from Lygus spp. nymphs in our study, 75% to 80% tested positive as Peristenus spp. and 76% of these matched the endonuclease digestion banding pattern of P. howardi. The identity of the remaining 20% to 25% of the parasitoids is not known.