Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2005
Publication Date: 6/5/2005
Citation: Day, W.H. 2005. Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa. Biological Control 33:368-374 Interpretive Summary: The tarnished plant bug (TPB) damages a variety of important crops in the eastern 3/4 of North America. The author established Peristenus digoneutis, a parasite from Europe, to provide biological control of the TPB. It has reduced TPB numbers by 65% in alfalfa for 10 years, in NW New Jersey. Damage by the TPB to apples has been reduced by 63% in New Hampshire, during the same period. The parasite is causing moderate to high mortalities of TPB in red clover, strawberries, vetch, and is likely reducing damage by the TPB to many crops. However, there have been some theoretical concerns that native parasites of the TPB might be eliminated, or native parasites of other mirids might be reduced, by the more efficient European parasite. Field observations over nearly 2 decades have shown that neither of these concerns actually occurred, confirming the safety of classical biological control using braconid wasp parasites.
Technical Abstract: High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the European parasite P. digoneutis Loan became well-established, average parasitism of the first and second generations increased to 61%, and tarnished plant bug numbers dropped by 65%. This reduced host density caused a decline in parasitism to 23%, with P. pallipes persisting at low levels. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest, increase its parasitism rate, or eliminate the native P. pallipes. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs was increased to 22% by the introduced (univoltine) parasite, P. conradi Marsh, and some reduction may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the tachinid parasite of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.