52 • Alternatives to Insecticides for Managing Vegetable Insects

Tarnished Plant Bug

Current Status of BiologicalControl of the Tarnished PlantBug in Northeast Alfalfa andResearch on Extension of ThisMethod to Other Crops

William H. DayResearch EntomologistUSDA Beneficial Insects Research LaboratoryNewark, Delaware

The tarnished plant bug (TPB), Lygus lineolaris(Palisot), is a native North American insect thatcauses moderate to severe damage to a large num-ber and wide variety of important crops. Yield andquality losses have been recorded on numerousfruit, vegetable, and seed crops, and also on for-estry seedlings and cotton.

Although the TPB is a native species, nearly all ofthe damaged crops are not native, and this is thoughtto be the reason why native parasites do not ad-equately control this pest. However, there are twoclosely related Lygus species in Europe, and theyare significantly parasitized on several crops there— so there is some potential for introducing Euro-pean parasites into the United States to reduce cropdamage by our TPB.

Alfalfa was selected for the initial research for sev-eral reasons: we had an extensive knowledge of itspests and their natural enemies, both in the north-eastern United States and in Europe; it is a widelygrown crop here, so it could serve as a parasite“reservoir”; it is infrequently sprayed with insecti-cides in the Northeast; and Lygus spp. are an im-portant pest of seed alfalfa in the northwesternUnited States.

Research on Lygus is complicated by the large num-ber of crops attacked and several difficulties withthe parasites (none of the previous attempts at sixdifferent locations were able to establish any para-sites). However, we have made encouragingprogress on alfalfa pests, having established Euro-pean parasites of the alfalfa plant bug (Adelphocoris)as well as of the tarnished plant bug.

Peristenus digoneutis Loan, which attacks the TPB,is a small wasp that lays eggs in the young nymphsand kills them before they are old enough to re-produce. It has spread from our original establish-ment point in northwestern New Jersey into sixadditional northeastern states (Pennsylvania, NewYork, Connecticut, Massachusetts, Vermont, NewHampshire) and is likely also in Quebec, Maine,and Rhode Island. It has two generations per yearand is well-synchronized with the two major TPBgenerations. In New Jersey, parasitism rates reached60%, which reduced TPB numbers in alfalfa by 75%.Unfortunately, P. digoneutis has not become estab-lished south of New York City, probably due toclimatic differences, so another species will haveto be found for warmer locations.

Cooperating scientists in three states have assistedwith following the dispersal of this parasite intonew areas. I also have cooperators in New York(K. Tilmon, Cornell University) and in New Hamp-shire (Allen Eaton, University of New Hampshire)who have recently begun to research the ability ofP. digoneutis to control the TPB in strawberries. InNew Hampshire in 1998, parasitism ranged up to55% on six farms, with an average of 15%. All para-

Tarnished plant bug

Session 4: Small Group Sessions by Crop or Insect Pest • 53

sites reared so far were P. digoneutis. Several years’work will be necessary to determine if this per-centage will improve over time, and whether a re-duction in TPB numbers and damage to strawberryyield and quality is occurring.

No research on vegetables has yet been started,but hopefully some will in the near future.

We have recovered a few P. digoneutis from seedalfalfa fields in Idaho, but it is too soon to tell if thisparasite is permanently established there. Whiledoing this work, we discovered a “new” (previ-ously unknown) and effective parasite of the re-lated “western TPB.” Further research will be nec-essary to learn if either or both of these parasitescan control Lygus in seed alfalfa. I have also re-leased the Idaho parasite in Delaware, in hopes ofobtaining biological control of the TPB in the mid-Atlantic region.

The results to date have been encouraging. My hopeis that sufficient research will be done during thenext decade in the northeastern United States todevelop permanent biological controls for the tar-nished plant bug on many fruit and vegetable crops.This will require increased research efforts, andsome of you may be able to assist with this impor-tant task.

Tarnished Plant Bug

Jake GuestNorwich, Vermont

Tarnished plant bug (TPB) is by far Vermont’s mostimportant vegetable and berry pest. All organicgrowers as well as those conventional growers try-ing to reduce pesticide use suffer moderate to se-vere losses caused by the feeding activity of thisubiquitous native bug.

TPB is a highly adaptable, cosmopolitan feeder ableto feed and breed on a remarkably large numberof crop and noncrop plant species. Moreover, itoverwinters successfully; has few significant natu-ral enemies or diseases; and is able, as an adult, tomove freely from host to host. TPB can produceseveral generations in a season and is moderatelyactive even in the cool of spring and fall.

Crop damage from TPB feeding can take manyforms, depending on the crop, and includes blos-som abortion (peppers, eggplant), deformation ofgrowing tips (celery, spinach), and cosmetic dam-age to marketable parts of crop plants (broccoli,lettuce). Damage to individual crops may be lightto severe, but because so many crops are likely tobe involved, economic impact on Vermont’s typi-cal mixed vegetable and berry farms can be sub-stantial, especially for those farms relying onnonchemical pest control.

A recent informal survey of several Vermont veg-etable and berry growers revealed that economicloss from TPB may be much more extensive thanpreviously assumed:

1. Many growers are apparently unaware thatlosses they have observed were the result ofTPB feeding. Blossom drop in peppers andeggplant, for example, is often attributed to tem-perature extremes rather than TPB. Likewise,deformation of growing tips, as in celery andspinach, is often blamed on boron or calciumdeficiency.

2. Some growers have simply stopped growingcertain crops because they have been unableto control TPB damage. Summer lettuce is anexample. Other growers have either stoppedgrowing organic strawberries or have neverstarted, solely because of likely severe cat-fac-ing of berries from TPB feeding. Growers oftenstate that fear of TPB feeding damage was theonly reason for not growing an otherwise prof-itable crop.

3. Most nonchemical growers have been unableto find adequate methods for controlling TPB,even with organically approved sprays labeledfor TPB. Equally discouraging results have beenachieved with row covers, parasitic wasps, andrepellent sprays. Generally, a lot of money hasbeen spent with few positive results. Onegrower spent $8,000 on a large, tractor-mountedbug vacuum, only to find that TPB was able tofly ahead of the machine and escape.

54 • Alternatives to Insecticides for Managing Vegetable Insects

Discussion: Tarnished PlantBug

Bill Day: The USDA (U.S. Department of Agricul-ture) lab has been in Newark, Delaware the past25 years and was in Moorestown, New Jersey for50 years before that, so it is relatively old. The labo-ratory has five scientists along with support staffand has a mission to develop classical (that is, per-manent) biological controls for agricultural pests,primarily those that have been imported throughcommerce; the bugs are here and their enemiesare not. The USDA has a similar lab in Europe thatidentifies the natural enemies of our problem in-sects and ships them to Newark. The Newark labtries to establish biological controls, to reduce thelevels of pests and eliminate chemical use. Theyare often successful, but sometimes can only lowerpopulations somewhat.

Audience: How do you identify which insects tostudy and bring in natural enemies for?

Bill Day: We talk to farmers and agricultural agents.If they have a problem, we will try to fit it into ourschedule, though we usually must finish otherprojects before we can start new research. The ini-tial research focuses on feasibility: Is the pest offoreign origin? Are there effective natural enemiesthere? Are they safe?

Audience: What about flea beetles? They seem tobe controlled in Europe but not in the United States.

Bill Day: If someone could get the name of thatflea beetle to me, I would work to put it forward. Ittakes us a number of years to start a project, but Iwill start the process.

Audience: Phyllotreta cruciferae.

Bill Day: Thank you. This is a pest that was intro-duced accidentally from Europe. I am told it hasbecome an important pest and warrants some bio-logical control research, but I am not aware of anybeing done. (See session on flea beetles, page 32,for more information.)

There are three kinds of natural enemies of insectsthat are used in classical biological control: para-sites, predators, and pathogens. Parasites, like para-sitic wasps that lay eggs in insect eggs, are very

effective and are used most frequently in biologi-cal control. Predators, like lady beetles, also killpests. The difference is that one parasite will killone pest, while one predator will kill many pests.However, the mother of a parasite will lay manyeggs, and parasites are usually more specific so theywill reduce a single species of pest insect on thecrop, which a general predator won’t necessarilydo.

About 40% of agricultural insect pest problems inthe United States are imported. They are the resultof insects coming here without their natural en-emies. The Europeans do not put a large emphasison insects that are under control there, so the USDAstarted a lab in France early this century to researchtheir natural enemies of our immigrant pests. Ourlab works with the lab in Europe to develop classi-cal biological control. In classical biological con-trol, you release the parasite or predator, then youfollow up to make sure it is established and to seewhat effect it has on pest populations. Once it isestablished, it is permanent. You never have to re-lease it again. In “augmentative” biological control,you put out natural enemies that don’t last long soyou have to keep putting them out. You must keepbuying them, and it becomes another input cost.

Biological control did not have a good reputationin the past. The lab’s work with the alfalfa weevilreversed that. The larva of the alfalfa weevil doesmost of the crop damage; the adult lays 3,000–4,000eggs. Our lab worked over a ten-year span withour European lab to introduce 13 parasites. Sevenestablished in northeastern states, four did a bang-up job reducing weevil populations. All seven areparasitic wasps. In the late 1960s and early 1970s,the sales of insecticides used to control of alfalfaweevil plummeted in the Northeast due to biologi-cal control. I estimate savings of $100 million a yeardue to this one project. In addition, the farmer hasto do nothing to keep this going; the natural en-emies are out there and are doing it all by them-selves.

By 1984, I had determined that the small parasiteof the TPB, Peristenus digoneutis, was establishedin northwest New Jersey. It had been released in anumber of different places since it is not possibleto be certain in advance where a natural enemywill establish. By 1996, it had spread to parts ofNew York, Vermont, New Hampshire, Connecticut,

Session 4: Small Group Sessions by Crop or Insect Pest • 55

Massachusetts, and Pennsylvania. Some additionalestablishment was attempted, but the parasite seemsto move very well by itself in the direction of pre-vailing winds (northeast). By 1996, it was estab-lished in 37 counties in seven states. It had spreadhundreds of miles northeast but only a few milessouth. The parasite does not seem to like a warmclimate. The parasite came from northern France ata latitude about that of Montreal and was not foundin Mediterranean regions to the south. You can’talways take a parasite from another country andexpect it to establish here. We will need to findanother species to replace it south of New YorkCity, and our lab is working on this.

Audience: Is it found in Scandinavian countries?

Bill Day: No one knows. The Lygus bugs it attacksare generally not a problem there so they haven’tresearched it. I am assuming that the parasite willspread west, north, and east. It is probably in Mainealready.

Audience: Is there any impetus to spread it by he-licopters over larger areas?

Bill Day: We should probably let nature take itscourse. We tried to spread it early on, and it didn’twork. The parasite is very delicate and difficult toraise. This parasite will probably take care of ourproblems in the Northeast, but it is not yet certainhow many crops will benefit.

The female lays her eggs inside the nymph of theTPB. They hatch, eating and killing the nymph. Theypupate underground and overwinter there, too.There are two full generations of the parasite inNew Jersey every year, coinciding with two full gen-erations of the TPB; there is sometimes anotherpartial third generation of both. The parasite is do-ing a good job controlling the TPB. Since parasit-ism started to become common in 1984–1985, theTPB/alfalfa ratio has taken a nose-drive. Subse-quently, parasitism has also fallen as the TPB hasbecome scarcer.

The parasite has a good effect on TPB in alfalfa,but will it have the same effect on other crops?

In New York, Kelley Tilmon is looking at parasitesin strawberries. In her research, she found that threeof four fields had parasites. The parasite is there-fore going into strawberry fields by itself. Alan Eaton

in 1997 looked at strawberry fields in New Hamp-shire and found an average damage due to TPB of$300/acre. In 1998, he sent samples to our lab foranalysis; we found the parasite in four of six fields,with parasitism ranging from 5 to 55% in the fourfields. Two of the three fields that had low levels ofparasitism had been treated earlier with insecticidefor a different pest.

Audience: The numbers are a little deceptive. Whenyou discuss parasitism rate, you’re not looking ateffect on overall population. Perhaps the overallTPB population is declining as well.

Bill Day: The first step is to find the parasite instrawberries. Once this has been done, multi-yearstudies are needed to look at its impact, and wealso need to examine its effect on yield and qual-ity. In general, if you can kill a third of bugs with anew parasite, you have a good shot at biologicalcontrol, because this adds to the existing mortality.

I am also interested in alfalfa seed and carrot seed.Carrot seed used to have a low germination rate of20–30%. In the 1930s, researchers showed that wasnot an inherent quality of the carrots; instead, itwas due to the TPB. When TPB was controlled, thegermination rate went up to 70–80–90%, compa-rable to other crops.

We haven’t quite reached the rainbow in this project,but we have made some progress. Eight peoplehave tried to establish parasites for the TPB inAmerica, and I was the first one to succeed, prob-ably due to my persistence. The parasite is nowdoing very well in alfalfa and is now flying intostrawberries. We want to find some cooperators tolook at lima beans and other crops.

Audience: And lettuce?

Bill Day: Including lettuce.

We need some research collaborators in the NewEngland area to look at the effects of the TPB. Ifthey’re in an area where the parasite is, we shouldlook at the effect it is having. It will be another tenyears of work before we fully understand the ef-fects on many of the crops that the TPB damages.

Audience: Are you researching how vulnerablethese parasites are to standard insecticides in thefield?

56 • Alternatives to Insecticides for Managing Vegetable Insects

Bill Day: No. They may be vulnerable, but I amtold that growers don’t put too many insecticidesin strawberries. There are probably times of theyear that you can release the parasites without hav-ing them killed. TPB in New Jersey have two maingenerations (20 June and 20 July). The parasitepopulations peak at just around the same times, sothey come out of their cocoons as adult wasps alittle earlier. If you spray at the beginning of Juneor the beginning of July, when the cocoons are stillin the ground, there is no danger of killing them.

Audience: I was wondering whether the distribu-tion on the map shown just shows where your col-laborators are.

Bill Day: We found most of these new parasiterecords ourselves with help from Pennsylvania,Massachusetts, New Hampshire, and New Jersey.The distribution follows river valleys and roads andwhere the crops are, not collaborators.

Audience: Overwintering?

Bill Day: In the ground, in a cocoon.

Audience: I was wondering if there’s a potentialbeneficial habitat we can provide on the farm forthis parasite.

Bill Day: Well, we haven’t really researched this. Itmight help to plant some alfalfa to provide a year-round reservoir for them. TPB are supposed to haveover 300 host plants, most of which are weeds, butwhether the parasite is in all these plants, we don’tknow.

Jake Guest: My wife and I have a certifiable organicfarm in Vermont. We have 50 acres including covercrops and green manures, and about 25 acres incultivation including sweet corn. When Kim hadinitially invited me to come to talk, she assumed Iknew about research on fungi to control TPB thatis going on at the University of Vermont, but theyhaven’t found anything. In the last week, I calledup several farmers and talked to them about TPB.It is still a major problem, just like in the previoussurvey.

The economic impact of TPB is probably muchgreater than people have been saying. For most ofthe growers, the figure they gave doesn’t includethe full estimate. It’s expensive to be resigned to

TPB and some amount of loss. Then there’s theother big problem with TPB — what you do withit? Several people have tried sprays of various kinds.Sabadilla is difficult to use and not necessarily ef-fective. I’ve tried copper rotenone dust almost ev-ery day but they would just walk over the dust.People have tried other forms of rotenone and pyre-thrins, but it’s difficult for a grower to assess howwell the treatments are working. You don’t see thetarnished plant bugs dead. The only way to assessresults is to notice less damage. Pyrenone® is some-what effective but only allowed in Maine and Ver-mont. Conventional growers don’t have a problemwith strawberries, since they can spray them withmalathion, but they don’t want to spray lettuce andbroccoli, because malathion smells bad, and thedamage is done right around the time you have toharvest. No one has tried neem products, so I can’treport on that.

Some people have tried row covers, excluding thebugs out of the crop. This works fairly well in straw-berries, but row covers are labor-intensive. TPBdoesn’t seem to overwinter in strawberries, sincethey aren’t found feeding on strawberries in latesummer.

Anaphes iole (another parasite of TPB which is com-mercially available) is not doing so well. One farmerwho had released them for three years, ten daysapart is going to do it again but is discouraged. It’sexpensive, about $70 per release per acre.

Audience: Did this parasite (Anaphes iole) comefrom California?

Jake Guest: Yes, originally.

Audience: I think The Green Spot in New Hamp-shire sells it. [Editor’s note: It is listed in the cata-logue from The Green Spot. The addresses of sev-eral suppliers are in listed under “Sources of Com-mercially Available Biological Control Agents” inappendix B, page 66.]

Jake Guest: The growers using it might also get itfrom California. The new day-neutral strawberriesproduce continuously, and in California they can’teven spray enough. The rumor is that they are us-ing Anaphes on a regular basis and getting goodresults.

I think that’s still up in the air. It’s expensive to buy

Session 4: Small Group Sessions by Crop or Insect Pest • 57

ably you could also clean the sticky trap off andreuse it, adding new “Tanglefoot” or another simi-lar product.

Jake Guest: The traps also collect everything, in-cluding beneficials. One company a few years agocame up with a tractor-driven vacuum machine thatdrives down a row and sucks them up. It’s designedto smash them in the blades. But Randall McGerrysays it doesn’t work, because they outflew the ma-chine; it didn’t draw them in. He had bought amachine for $8,000 ten years ago; it was a proto-type. Now that I’m growing strawberries myself, Irealize there might be some mechanical things todo. If you can get rid of adults, then you couldreduce the whole population. The conventionalwisdom is that you don’t want to mow alfalfa whenstrawberries are in bud. One grower in Maine, whowas surrounded by dairy farmers, puts plantings ofclover around his field, and he thinks that they preferthe clover and they go there instead of strawberryfields. He controls when the clover is cut, after thestrawberries are done. But then you are feedingthem and increasing their populations. There’s noreason for euphoric optimism, but there are a fewthings that people have tried that seem to work.Most of them are cultural practices. I’m convincedthat keeping weeds down, especially red-root pig-weed, will help. If I can keep the weeds down,then I can control much of what goes on in myfield.

On my own farm, I do not use clovers very muchin any of my rotations, because the majority of mynutrition source is hen manure, so I don’t needmore nitrogen. I use hen manure to grow grass(rye or sudan) instead to increase organic matter. Idon’t have legumes in my crop rotation. Some ofthe speakers here this weekend have been talkingabout the benefit to the biological balance of hav-ing legumes, but I don’t know what to say aboutthat. Some of the larger growers plant TPB-suscep-tible crops in the center of fields away fromhedgerows, and there’s something to be said forthat. Timing of mowing is crucial. Changes in cul-tural practices seem to hold the most hope.

In desperation, the Vermont vegetable and berrygrowers association heard that the University ofVermont entomology labs had done successful con-trol of thrips for the maple industry using fungi. Weapproached them to work with TPB. We provided

them and put them out in the right amounts. Maybethey could afford more than we could, since yieldsare higher in California. There is research lookingat nymphal parasites, too. It’s still small-scale.They’re not going to make any recommendationsto growers yet.

There doesn’t seem to be anything else promisingout there for growers to use now. When we heardabout Peristenus, the growers in Vermont soonfound out that no one is producing them commer-cially, but Bill’s responses are promising.

Audience: Are there any specific procedures thatmust be followed to release Peristenus? How oftenwould you need to make releases?

Bill Day: The wasps must be sent by overnight mailand in special containers so they don’t die enroute.

To release them at the right time, when there are avariety of sizes of nymphs, you should be able torelease two times in June and twice in July. It takesten months to find out if they have successfullyoverwintered, because they diapause (spend tenmonths in the ground), so you won’t be able to seeif they have survived until the next March.

Audience: If they have to spend ten months in theground, that could really disrupt tillage.

Bill Day: It might, especially in an annual crop likelettuce. You might want to plant some alfalfa, orthe wasps might be able to overwinter in strawber-ries, since they are a perennial.

Audience: Organic growers tend to keep strawber-ries around for two years, conventional growersfive to seven. Organic growers tend to have weedsaround, too. Maybe the wasps could overwinter inthem.

Bill Day: Maybe. There’s not much known at thispoint.

Audience: Some growers have used white stickycards to use track flight of TPB and then expandedso that they have one every ten paces along row.But using white sticky traps as a control at $2 pertrap is too expensive. Could you make the traps? Isthere a pheromone used on them?

Bill Day: No, I think you could make the traps. Itneeds to be a similar color to attract the TPB. Prob-

58 • Alternatives to Insecticides for Managing Vegetable Insects

them with a modest grant from our organization,and it was neat to see growers getting together withresearchers. They got a program going and a Hatchgrant for $20,000 to research fungi on TPB. Firstthey had to figure out how to rear TPB. They havea pretty good technique for raising them. They hada lot of isolates for fungi and collected more, fromall over the place. They came up with about thirtygood isolates and narrowed it down to about five.These are fungi that will attack TPB and will intime infect the bug and kill it. They had to developa bioassay technique. They started feeding the TPBbeans, but the beans were killing the bugs becauseof insecticide residues in beans. Now they’re grow-ing their own organic beans and broccoli. Theyhad to decide on temperatures, the size of cups,whether to cover them. They came up with a wayto collect the eggs; there’s a system where you takethe beans and wrap them in a certain kind of toiletpaper, and stick them in holes in PVC pipes in whichthe animals are inside. The TPB lay eggs in thetoilet paper around the bean, then the researcherstake the toilet paper and put it in a beaker anddissolve it, filter it out, and collect eggs. They putthe eggs in individual petri dishes and hatch themout. After they hatch, they take second-instarnymphs. They take ten out of each dish and put

them in amber containers, put the concentrates offungi in with them, shake them up, strain them,and put them in plastic cups. This bioassay begs alot of questions. It’s not the way we’d do it in thefield — we would never shake them up in solu-tion. After fungi grow, the TPB turn white and fuzzyand die.

This is going in the right direction and might be atool we can use. They have 95% mortality (in bio-assays) and are now figuring out concentration. Thenext question is the time frame before death. It’spretty basic research, and I’m not sure it’s ever go-ing to work, but you have to do it with such animportant pest.

Audience: Does this fungus live in the field? Doesit have a life of its own?

Jake Guest: I don’t know.

Audience: How do they make it grow? Do theyneed to let it grow on TPB?

Jake Guest: No, keeping it alive isn’t a problem.They can culture it. They are getting a high mortal-ity rate of TPB with the fungus, but it still may notwork in the field.