Tarnished Plant Bug Current Status of Biological Control of the Tarnished Plant Bug in Northeast Alfalfa and Research on Extension of This Method to Other Crops William H. Day Research Entomologist USDA Beneficial Insects Research Laboratory Newark, Delaware The tarnished plant bug (TPB), Lygus lineolaris (Palisot), is a native North American insect that causes moderate to severe damage to a large num- ber and wide variety of important crops. Yield and quality losses have been recorded on numerous fruit, vegetable, and seed crops, and also on for- estry seedlings and cotton. Tarnished plant bug Although the TPB is a native species, nearly all of the damaged crops are not native, and this is thought Peristenus digoneutis Loan, which attacks the TPB, to be the reason why native parasites do not ad- is a small wasp that lays eggs in the young nymphs equately control this pest. However, there are two and kills them before they are old enough to re- closely related Lygus species in Europe, and they produce. It has spread from our original establish- are significantly parasitized on several crops there ment point in northwestern New Jersey into six — so there is some potential for introducing Euro- additional northeastern states (Pennsylvania, New pean parasites into the United States to reduce crop York, Connecticut, Massachusetts, Vermont, New damage by our TPB. Hampshire) and is likely also in Quebec, Maine, and Rhode Island. It has two generations per year Alfalfa was selected for the initial research for sev- and is well-synchronized with the two major TPB eral reasons: we had an extensive knowledge of its generations. In New Jersey, parasitism rates reached pests and their natural enemies, both in the north- 60%, which reduced TPB numbers in alfalfa by 75%. eastern United States and in Europe; it is a widely Unfortunately, P. digoneutis has not become estab- grown crop here, so it could serve as a parasite lished south of New York City, probably due to “reservoir”; it is infrequently sprayed with insecti- climatic differences, so another species will have cides in the Northeast; and Lygus spp. are an im- to be found for warmer locations. portant pest of seed alfalfa in the northwestern United States. Cooperating scientists in three states have assisted with following the dispersal of this parasite into Research on Lygus is complicated by the large num- new areas. I also have cooperators in New York ber of crops attacked and several difficulties with (K. Tilmon, Cornell University) and in New Hamp- the parasites (none of the previous attempts at six shire (Allen Eaton, University of New Hampshire) different locations were able to establish any para- who have recently begun to research the ability of sites). However, we have made encouraging P. digoneutis to control the TPB in strawberries. In progress on alfalfa pests, having established Euro- New Hampshire in 1998, parasitism ranged up to pean parasites of the alfalfa plant bug (Adelphocoris) 55% on six farms, with an average of 15%. All para- as well as of the tarnished plant bug. 52 • Alternatives to Insecticides for Managing Vegetable Insects sites reared so far were P. digoneutis. Several years’ Crop damage from TPB feeding can take many work will be necessary to determine if this per- forms, depending on the crop, and includes blos- centage will improve over time, and whether a re- som abortion (peppers, eggplant), deformation of duction in TPB numbers and damage to strawberry growing tips (celery, spinach), and cosmetic dam- yield and quality is occurring. age to marketable parts of crop plants (broccoli, lettuce). Damage to individual crops may be light No research on vegetables has yet been started, to severe, but because so many crops are likely to but hopefully some will in the near future. be involved, economic impact on Vermont’s typi- cal mixed vegetable and berry farms can be sub- We have recovered a few P. digoneutis from seed stantial, especially for those farms relying on alfalfa fields in Idaho, but it is too soon to tell if this nonchemical pest control. parasite is permanently established there. While doing this work, we discovered a “new” (previ- A recent informal survey of several Vermont veg- ously unknown) and effective parasite of the re- etable and berry growers revealed that economic lated “western TPB.” Further research will be nec- loss from TPB may be much more extensive than essary to learn if either or both of these parasites previously assumed: can control Lygus in seed alfalfa. I have also re- leased the Idaho parasite in Delaware, in hopes of 1. Many growers are apparently unaware that obtaining biological control of the TPB in the mid- losses they have observed were the result of Atlantic region. TPB feeding. Blossom drop in peppers and eggplant, for example, is often attributed to tem- The results to date have been encouraging. My hope perature extremes rather than TPB. Likewise, is that sufficient research will be done during the deformation of growing tips, as in celery and next decade in the northeastern United States to spinach, is often blamed on boron or calcium develop permanent biological controls for the tar- deficiency. nished plant bug on many fruit and vegetable crops. This will require increased research efforts, and 2. Some growers have simply stopped growing some of you may be able to assist with this impor- certain crops because they have been unable tant task. to control TPB damage. Summer lettuce is an example. Other growers have either stopped growing organic strawberries or have never started, solely because of likely severe cat-fac- Tarnished Plant Bug ing of berries from TPB feeding. Growers often state that fear of TPB feeding damage was the Jake Guest only reason for not growing an otherwise prof- Norwich, Vermont itable crop. Tarnished plant bug (TPB) is by far Vermont’s most 3. Most nonchemical growers have been unable important vegetable and berry pest. All organic to find adequate methods for controlling TPB, growers as well as those conventional growers try- even with organically approved sprays labeled ing to reduce pesticide use suffer moderate to se- for TPB. Equally discouraging results have been vere losses caused by the feeding activity of this achieved with row covers, parasitic wasps, and ubiquitous native bug. repellent sprays. Generally, a lot of money has been spent with few positive results. One TPB is a highly adaptable, cosmopolitan feeder able grower spent $8,000 on a large, tractor-mounted to feed and breed on a remarkably large number bug vacuum, only to find that TPB was able to of crop and noncrop plant species. Moreover, it fly ahead of the machine and escape. overwinters successfully; has few significant natu- ral enemies or diseases; and is able, as an adult, to move freely from host to host. TPB can produce several generations in a season and is moderately active even in the cool of spring and fall. Session 4: Small Group Sessions by Crop or Insect Pest • 53 Discussion: Tarnished Plant effective and are used most frequently in biologi- cal control. Predators, like lady beetles, also kill Bug pests. The difference is that one parasite will kill one pest, while one predator will kill many pests. Bill Day: The USDA (U.S. Department of Agricul- However, the mother of a parasite will lay many ture) lab has been in Newark, Delaware the past eggs, and parasites are usually more specific so they 25 years and was in Moorestown, New Jersey for will reduce a single species of pest insect on the 50 years before that, so it is relatively old. The labo- crop, which a general predator won’t necessarily ratory has five scientists along with support staff do. and has a mission to develop classical (that is, per- manent) biological controls for agricultural pests, About 40% of agricultural insect pest problems in primarily those that have been imported through the United States are imported. They are the result commerce; the bugs are here and their enemies of insects coming here without their natural en- are not. The USDA has a similar lab in Europe that emies. The Europeans do not put a large emphasis identifies the natural enemies of our problem in- on insects that are under control there, so the USDA sects and ships them to Newark. The Newark lab started a lab in France early this century to research tries to establish biological controls, to reduce the their natural enemies of our immigrant pests. Our levels of pests and eliminate chemical use. They lab works with the lab in Europe to develop classi- are often successful, but sometimes can only lower cal biological control. In classical biological con- populations somewhat. trol, you release the parasite or predator, then you follow up to make sure it is established and to see Audience: How do you identify which insects to what effect it has on pest populations. Once it is study and bring in natural enemies for? established, it is permanent. You never have to re- lease it again. In “augmentative” biological control, Bill Day: We talk to farmers and agricultural agents. you put out natural enemies that don’t last long so If they have a problem, we will try to fit it into our you have to keep putting them out. You must keep schedule, though we usually must finish other buying them, and it becomes another input cost. projects before we can start new research. The ini- tial research focuses on feasibility: Is the pest of Biological control did not have a good reputation foreign origin? Are there effective natural enemies in the past.