SOYBEAN APHID

Research Update

Your soybean checkoff. Delivering results. A multi-pronged attack on soybean aphids Biological control, aphid-resistant varieties and aphid tracking systems

Every initiative at the North Central resistant sources there are, the tougher it Soybean Research Program has the same will be for aphids to overcome them. goal: helping producers improve their Checkoff dollars helped build the profitability. suction trap network that tracks aphid That’s why checkoff-funded researchers migrations and populations, as well as the spent years tracking down and studying Sentinel Plot Program, an early-warning The North Central Soybean Binodoxys communis, an exotic natural system for rust and aphids. Research Program (NCSRP) parasitoid from Asia that was released NCSRP also funded research on soybean is comprised of state soybean throughout the North Central region in aphids’ native natural predators and checkoff boards in Illinois, 2007. This tiny, stingless wasp effectively treatment thresholds so growers know Indiana, Iowa, Kansas, controls soybean aphids in China, and when to spray and when to hold off calling Michigan, Minnesota, Missouri, we’re hoping it’ll do the same for U.S. the custom applicator. Nebraska, North Dakota, Ohio, soybean growers. From biocontrol and genetic resistance South Dakota and Wisconsin. If Binodoxys establishes itself here and to early warning systems and treatment Established in 1992 to coordinate helps keep aphid numbers low, it also may recommendations, your checkoff dollars soybean production research lower the number of insecticide applications cover a lot of ground when it comes to efforts on a regional level, NCSRP needed. This is a classic case of natural helping you manage aphids. That’s your invests soybean checkoff funds biocontrol, and if it works, it’ll be one of soybean checkoff. Delivering results. in research programs to better the most successful in history. understand and manage soybean In another area, thanks to checkoff pests and diseases. support for germplasm screening at public institutions, aphid-resistant soybean varieties are on the way. Several universities are Jerry Wyse developing resistant lines, using different NCSRP President genetic sources of resistance. The more Haven, KS

www.planthealth.info For more information or to order copies of this soybean aphid research update, contact David Wright at 800-383-1423. Table of Contents

Aphid enemies from Asia...... 3 Special thank you to our insert print publication sponsor: When soybean plants are good aphid hosts ...... 5 Warrior with Zeon Technology® insecticide. Are You Ready to Increase in native parasitoids ...... 6 Fight Soybean Aphids? New guide identifies beneficial insects...... 7

Cover photo courtesy of Roy Scott, SDSU. Monitoring aphids via the suction trap network...... 8

Growers can track aphids online through the IPM PIPE. . . . 9

Aphid-resistant varieties coming soon...... 10 © 2008 North Central Soybean Research Program Revisiting the 250 treatment threshold...... 11

2 3

Reuniting old enemies

Releasing aphid enemies from Asia into Midwest soybean fields SDSU Scott, Roy of Courtesy

After three years of safety testing in O’Neil points to biological control quarantine laboratories – and another one examples in other crops. “Parasitoids from and a half years getting the government the Mediterranean have been successfully permits – checkoff-funded researchers got introduced to control alfalfa weevil,” he the go-ahead to release an “exotic biological explains. “Thanks to biological control, control agent” that attacks soybean aphids. alfalfa weevils went from being a significant This tiny, stingless wasp, calledBinodoxys pest problem that farmers were spraying communis, hails from China and Japan, most years, to no problem at all.” where it has been a long-time natural enemy of soybean aphids. It won’t eat Toledo During the summer of 2007, wasps were Researchers also spent years testing the host released in 30-plus locations throughout range of Binodoxys to make sure it won’t Minnesota, Michigan, Iowa, Illinois, disrupt non-target aphid species. According Indiana, South Dakota and Wisconsin. to O’Neil, “When you release a natural Release sites were a mixture of ag enemy, one of the big questions is, ‘Is it experiment stations and farmers’ fields, going to eat Toledo?’ We’ve done a lot of host near buckthorn whenever possible because specificity testing because we didn’t want to that’s where soybean aphids overwinter. release something that attacks everything. “The first step was to see if Binodoxys Binodoxys has a narrow host range, and would attack soybean aphids in U.S. soybean aphid is by far its No. 1 target.” soybean fields,” says Bob O’Neil, Purdue Scientists also have 15 to 20 other University entomologist. “We can’t prove parasitoid species still in quarantine. it at every location, but for the most part “It looks like a couple of those also have they did.” high host specificity to soybean aphids,” The next step will be forBinodoxys to says O’Neil. “We’re looking at those, too.” make it through the Midwestern winter. “They have to find something to live on How the wasp works during the winter,” says O’Neil, who Binodoxys lays an egg inside the soybean visited Asia several times looking for aphid. “As the egg hatches, the larva eats parasitoids (insects that use other insects the aphid from the inside out, starting with as hosts) that attack soybean aphids. the blood and ending with vital organs,” Fortunately, Binodoxys is from a region says Minnesota’s Heimpel. (The larva also that has the same climate, so weather spreads glue to keep the aphid stuck on the shouldn’t be a problem. soybean plant.)

It’s not a yellow jacket What could have been a problem – public Researchers hope this Binodoxys discomfort with the idea of scientists communis parasitoid – an enemy introducing a wasp into the Midwest – of soybean aphids – establishes has been minimal. “I’ve received a few itself throughout the North e-mails,” says George Heimpel, University Central region. of Minnesota entomologist leading the Binodoxys release. “When you say ‘wasp’ people think yellow jackets. But Binodoxys is completely different,” he adds. “That’s why we call them tiny, stingless wasps.” Courtesy of David Hansen, U of Minn.

2 3 Courtesy of Chris DiFonzo, MSU

Once the larva is done feeding, it goes low. So I think Binodoxys is probably better through the pupal stage, which involves adapted to low levels of aphids. spinning silk on the inside of the dead “I don’t think they’ll be very good at aphid skin. The aphid skin hardens, partly knocking down high aphid levels. But due to the silk, to form a puffy shell called once levels are low, they’ll keep them low,” a mummy. he continues. “If aphid levels spike, then Mummies look like puffy brown versions Asian lady beetles have a better chance of Releasing Binodoxys of the aphid, or sesame seeds. The adult knocking them back.” communis wasp cuts a “poptop” hole in the mummy The problem with that tag team – Asian and emerges. The mummy stays attached lady beetles and Binodoxys – is that they’re University of Minnesota to the plant, thanks to the glue. “What’s competitors, not partners. “The beetles Entomologist George Heimpel nice about the mummies is they’re easy to don’t mind munching on Binodoxys eggs says researchers tried several detect in the field, so you’ll know whether within mummies,” Heimpel adds. “My different methods of releasing you have Binodoxys,” Heimpel explains. hope is that eventually, Binodoxys can Binodoxyis communis last summer. keep aphid numbers so low that lady “Early in the season when Binodoxys emerging from beetles aren’t interested in visiting aphid levels were low, we used a mummified aphid body soybean fields. mesh-covered insect cage over a “Asian lady beetles tend not to lay eggs square meter of soybean plants. in fields with low aphid numbers,” he We removed the soybean aphid explains. “I’m hopeful that Binodoxys will predators (i.e., Asian lady beetles) also suppress them, because I think Asian from the cage, so aphid numbers lady beetle numbers are out of whack from built up enough for the feasting on aphids. And other than farmers, Binodoxys wasps to parasitize. most people hate Asian lady beetles.” Then we added potted soybean plants from a greenhouse that What’s next for Binodoxys had lots of Binodoxys about to O’Neil says checkoff-funded researchers hatch from aphid mummies. will continue releasing Binodoxys in “The idea was to get aphid overwintering habitats, to continue Binodoxys to establish within Courtesy of Matt O’Neal, IA State establishing the population. “It’s up to the the cages and reproduce, so we Keeping aphid levels low bugs, but we’ve given them every chance. tried waiting 10 days for one Heimpel says if we do eventually get aphid “If Binodoxys takes off,” O’Neil adds, generation of wasp, and three control from Binodoxys, it’ll take a few “farmers won’t be paying attention to weeks for two generations years. “Aphid densities in China are very aphids anymore.” before removing the cages,” Heimpel explains. “What worked best was waiting three weeks, when we had 100 to 500 mummies per plant – and 40 to 50 plants – inside the Read more about it cage. Adult wasps were taking Dan Mahr, entomologist at the off from second-generation University of Wisconsin, developed mummies and dispersing a Web site specifically about the through the field.” Binodoxys communis release, as well as other biological control efforts. Visit www.entomology.wisc.edu/sabc to read more about these projects, and to view photographs of Binodoxys, mummies and other beneficial natural enemies to look for in your soybean fields.

4 5 Courtesy of David Hansen, U of Minn. Aphid feeding is a double-edged sword When they feed, aphids’ piercing mouthparts (called stylets) are inserted between the soybean plant’s cells, where they tap into the nutritious phloem sap. “Aphids suck the nutrition out,” says John Reese, Kansas State University entomologist. “They also pump salivary secretions into the plant, and we think what they’re injecting is very damaging. The combination of what they’re taking out and pumping in reduces the plant’s rate of photosynthesis, and causes all sorts of plant responses.” Researchers are studying these responses, and how different varieties vary in their Host plant response and a new predictive model sensitivity to aphids. “The goal While some scientists are tracking when it was in the vegetative growth is to find varieties that are more whether Binodoxys communis survives phase,” he explains. tolerant to aphids,” Reese adds, and thrives in the Midwest, others are “so the plant can continue to researching the soybean plant itself New online aphid produce in spite of an aphid – and when it serves as the best host for population predictor attack, and without placing soybean aphids. Ragsdale’s team is developing a new selection pressure on the “Picture a graph that resembles the mathematical model that will predict aphid population.” mouth on a smiley face,” says David aphid population growth and include Ragsdale, University of Minnesota the smiley face phenomenon.

entomologist. “You’ve got high points “The current model is solely driven Courtesy of Greg Zolnerowich, KSU at both ends, and a low point in the by temperature,” he says. “It tells you middle. That’s what we get when we what the maximum possible growth rate look at the quality of the soybean plant could be, given those temperatures. It as an aphid host over the course of the gives you the worst-case scenarios, but growing season. Early in the season doesn’t take into account plant quality, (vegetative growth stages) and again natural predators, plant variety or late in the season when seeds are filling, bad weather. soybeans are great aphid hosts. “The new model will incorporate “The poorest plant quality is when the concept that the soybean plant pods are forming (R3), elongating (R4) is not a great host during part of its This aphid is hooked up to an and seeds begin to develop (R5). The growth phase,” Ragsdale adds. “It EPG (an electrical penetration vegetative growth has stopped, and also takes rainfall into account. For graph, which is the aphid the plant is putting all its emphasis on example, if a one-inch rainfall occurs equivalent of an EKG). By reproduction, on the pods. That’s the in one hour in association with high passing an electrical current low point.” winds accompanying a thunderstorm, through the plant and the aphid, Ragsdale says that’s when farmers aphid mortality can exceed 60 percent researchers can tell what cell the see white dwarves. “Aphids get smaller – especially in the vegetative growth aphid is feeding in, how long it’s and don’t reproduce very well because stage, when aphids are at the top of the feeding, and how the cell responds. the plant isn’t a very good host. Their plant and exposed. They get knocked lifetime reproduction is reduced by down and thrown into the mud, and 70 percent.” they can’t get out.” Then the plant starts to mobilize You can find the University of all the stored photosynthate and seeds Minnesota’s newly revised aphid begin to fill (R6). “At R6, the soybean population predictor at www.soybeans. plant is again as good a host as it was umn.edu.

4 5 An increase in natural parasites Researchers report seeing more native parasitoids in 2007

Besides the exotic Binodoxys communis parasitoid that researchers imported from Asia and released in the Midwest last summer, native parasites also have been popping up in North American soybean fields. “Scientists in several states report seeing more parasitoids in 2007,” says Chris DiFonzo, entomologist from Michigan State University. “It was very striking, even in Michigan. U of Courtesy of Bob Ellingson, Wis. We had this little black parasitoid that I’d never seen before,” DiFonzo says. “In Ontario, they were seeing the same thing.” Tracey Baute, entomologist with the Aphelinus albipodus Ontario Ministry of Agriculture, Food and Rural Affairs, identified two types of parasitoids in 2007. “We believe the dominant one was Aphelinus spp., though taxonomists are still determining which species it is. It wasn’t released here, so we’re How important are natural wondering if it came along with soybean predators for suppressing aphids from their origin country. Initially

aphid populations? “Pretty we thought it was Aphelinus albipodus, Courtesy U of Cal. of JK Clark, important,” says Matt O’Neal, which was originally released in the United Iowa State University States to control Russian wheat aphid.” entomologist. Several In Minnesota, researchers discovered researchers just completed something else entirely. “They’re called a study on the impact of Lysiphlebus testaceipes, and we first found predators and whether their them at relatively high levels back in Lysiphlebus testaceipes impact varies with the 2003,” says University of Minnesota landscape. In 22 locations, Entomologist George Heimpel. “It’s interesting,” she adds. “Our cropping more than 50 percent of fields “I thought they’d move into soybean system here is very similar to Michigan were kept below threshold by fields, but then we didn’t see them again and Ohio, yet they’re not seeing the same predators. “In fields where the until 2007,” he adds. Although there were levels of parasitoids. We’re investigating predators’ impact was not as more of them than in 2003, “Even at why.” great, the area was surrounded higher numbers the total percentage was As for aphid infestations in Ontario, “In by corn and soybeans. When still very low. In one-third to one-half of 2007, we experienced an outbreak early, you have more diverse land- fields, we saw 2 percent native parasitism.” in late May/early June, on early emerged scapes, predators can find food beans,” Baute says. “We had good weather and a place to spend the win- Good guys winning in Canada here and planted early, and we think they ter, so there are more of them In Ontario, parasitism levels are may have blown in from the United States. and their impact is greater.” significantly higher. “We did a survey “We found unifoliate stage soybeans in 2007, and preliminary results show that already had mummies on the plant. between 10-25 percent parasitism rates by The parasitoids reacted immediately to the Aphelinus spp. alone at several locations the early aphid infestation. The good guys

Courtesy of Craig Grau, U of Grau, Courtesy of Craig Wis. across the province,” Baute says. knew where to go, and I’m referring to

6 7 Guides to the good guys A new publication that helps farmers identify beneficial insects in soybeans is available. Funded by the NCSRP and the parasitioids, not the aggressive Winged soybean aphid written by University of lady beetles.” Wisconsin Entomologist Dan Baute says growers hesitated to spray Mahr, it’s publication #NCR481 and gave beneficials time to work because – Biological Control of Insects & they were seeing such a difference in the Mites. Contact your Extension levels of natural enemies. “Growers are soybean entomologist for a copy, taking the time to identify natural enemies or download a PDF from the in the field, observing their impact and, UW Extension Web site at http:// in many cases, watching them take aphid learningstore.uwex.edu. populations down below threshold.” You also can order a small pocket flip guide to carry in The immigration problem the field, called Identifying According to David Ragsdale, University of Natural Enemies in Crops and Minnesota entomologist, “Natural enemies Landscapes. It’s Michigan State can do a great job of controlling aphids Courtesy of Roy Scott, SDSU University Extension Bulletin as long as there isn’t an influx of winged E-2949, by Mary Gardiner, aphids. I’ve had consultants call and tell me, events, but they can identify fields that are C. DiFonzo, M. Brewer and ‘I’ve checked a field seven times, and the at greater risk for explosive aphid growth. T. Noma. It was developed as aphid population is staying the same.’ That’s Later planted beans are at higher risk, for a result of grower requests for because the natural enemies are keeping the example, because aphids are attracted to more biocontrol information aphid population in check. plants in vegetative phases as opposed to after soybean aphids arrived. “You can tolerate a moderate number reproductive phases. Early (April) planted Order a copy or download a of aphids for many weeks and not have a beans in Michigan and Ontario have gone PDF at www.emdc.msue.msu. yield response,” Ragsdale says. “It’s those over threshold in the vegetative stage after edu/inventorysearch.cfm. immigration events – where aphid populations infestation by large numbers of winged

build and produce winged aphids, which fly migrants from buckthorn. Courtesy of Eileen Cullen, U Wis.of off to colonize other fields – that we can’t get a “Unfortunately, the only way to detect handle on. At that point, no natural predator an immigration event is to be in your in the world can keep up.” fields counting aphids and checking them Ragsdale doesn’t think researchers will regularly,” Ragsdale says. ever be able to predict mass migration

Speed scouting a speed scouting worksheet, visit www. Entomologists at the University of soybeans.umn.edu/crop/insects/aphid/ Minnesota have developed a soybean aphid_sampling.htm. What’s with white dwarves? aphid “speed scouting” method to help you “Typically, a baby aphid is green save time sampling and making treatment or yellow and grows fast,” says decisions. The new method is used to George Heimpel, University of estimate when fields are at the 250 aphid Minnesota entomologist. “White threshold. The sampling cut-off point is 40 dwarves are a lighter color, aphids per plant. If a plant has less than smaller and grow more slowly.” 40 aphids, consider it non-infested. If Why are they produced? “One you’ve counted 40 aphids (counting above theory is that the host plant 40 isn’t necessary), consider the plant quality is low,” he explains. infested. Gathering several speed scouting “You tend to get white dwarves counts – scattered randomly throughout on old, yellow leaves.” Another a field – will lead you to one of three theory is natural enemies. “If you decisions: treat, don’t treat, or resample expose a colony of aphids to Asian in 3-4 days. For more information and Courtesy of Chris DiFonzo, MSU lady beetles, they produce more white dwarves. Predators don’t recognize them as well.”

6 7 Monitoring aphids via the suction trap network Measuring fall migration helps predict what you’ll face next summer

“We have 42 suction traps collecting because a lot of biology happens between soybean aphids in 10 states,” says Dave fall and spring,” Voegtlin explains. “Weather, Voegtlin, the Illinois Natural History planting time and natural predators are all Survey entomologist in charge of the factors that can influence what happens.” checkoff-funded suction trap network. The traps are basically big tubes roughly Other factors affecting aphids 25 feet tall, high enough to catch winged, During the fall of 2006, for instance, “We migrating aphids. At the base of each tube saw an unprecedented fall flight of aphids is a jar filled with preserving fluid. Fans making it back to buckthorn and laying suck aphids into the tube, and aphids are eggs. In Indiana, Illinois and southern preserved in the jar. Michigan, we found places where 100 “Every week, we monitor the traps and percent of randomly selected buckthorn count the aphids, beginning the end of twigs were infested. May and running through mid-October,” “So all these aphid eggs hatched the last Voegtlin says. Results are reported on a week of March 2007, and then we had a Web site – www.ncipmc.org/traps – where hard freeze the first week of April. That growers, entomologists and crop consul- killed all the leaves and the aphids as well,” tants can track soybean aphid populations. Voegtlin says. “Quite frankly, I don’t know how bad the summer of 2007 would have Fall counts forecast future outbreaks been without that hard freeze.” The number of winged aphids caught in In Michigan, summer heat attacked the September and October during their fall aphids. “They appeared early and in high flight back to buckthorn is used to forecast numbers in 2007,” says Chris DiFonzo, aphid outbreaks the following year. Michigan State University entomologist. Generally, high fall flight counts mean “Then the first week in July, we had aphid problems in the coming year. Low unseasonably high temperatures before rows fall flight numbers mean aphids will be closed, and the aphids literally baked on more scarce next year. the soybean plants. They never recovered.” “Of course, it isn’t always so clear-cut Western Wisconsin had high aphid when there are high aphid numbers, numbers in 2007, while the eastern part of

Aphids a problem in other crops “Aphids don’t just affect soybeans,” says Chris DiFonzo, Michigan State University entomologist. “They’re affecting the whole farming community, spreading viruses like cucumber mosaic, zucchini yellow, and watermelon mosaic in vegetable crops. Infected pumpkins look lumpy, and rot from the inside out. Potato viruses are a concern, too.” And at the University of Wisconsin, researchers are looking into whether soybean aphids are a vector for viral diseases in snap beans and green beans. Courtesy of Chris DiFonzo, MSU Courtesy of Chris DiFonzo, Courtesy of Chris DiFonzo, MSU

8 9 Put that in your PIPE… The Pest Information Platform for Extension and Education (PIPE), www.sbrusa.net, now includes soybean aphids. Land- that aphid numbers would keep building Grant University Extension and every year, and we don’t see that. So I Integrated Pest Management think it has to be the predators.” (IPM) specialists monitor soybeans for soybean aphids Not so great for hot spots from late vegetative through full In Minnesota, where buckthorn thrives, pod stages. The IPM PIPE aphid farmers in some areas face aphid outbreaks map provides a real-time picture every year. “We were hoping the suction traps of soybean aphid densities in could help us predict summer hotspots and sentinel soybean fields. “PIPE immigration events,” says David Ragsdale, takes the pulse of soybean aphid University of Minnesota entomologist. trends in the North Central “Unfortunately, that hasn’t been the case. region, but you still need to The traps can tell us what just happened, but scout fields on your farm to they don’t help us predict much about aphid make a treatment decision,” populations in a specific location. They do says Eileen Cullen, University work very well telling us what’s moving in of Wisconsin entomologist. Aphid eggs the fall and spring.” on buckthorn Extension entomologist Much like Wisconsin, Minnesota’s Courtesy of Dave Voegtlin commentary shared via the PIPE fall 2007 trap capture was the lowest helps farmers become informed the state generally had very low densities, researchers had ever seen. “Based on that, quickly about soybean aphid well below economic threshold. we expect low aphid populations in 2008. IPM practices. Explore the “I view this as a regional pest in scope,” But be careful – this does not mean aphids soybean aphid page at www. says Eileen Cullen, University of Wisconsin will be absent in 2008,” Ragsdale says. sbrusa.net/cgi-bin/sbr/public. entomologist. “Even in an aphid year, It also doesn’t mean scouting won’t be cgi?pest=soybean_aphid. there are fields that don’t reach economic necessary. “If you count 200 aphids one threshold. And in a low aphid year, there week, and 275 the next, predators are are fields that do. Region-wide, there is a doing a good job,” Ragsdale adds. “If lot of variability. That’s what makes field you jump from 200 to more than 600

aphids in a few days, then the predatorsIdentification of Soybean Aphid & Look-alike Similar-looking Species Whitefly Species scouting so important.” Species Several other aphid species feed on soybean, but they are Various whitefly species are known to feed on soybean but The soybean aphid, migratory and rarely colonize soybean. One that is have never been known to cause economic damage. Bigeyed Bug, Geocoris Species Aphis glycines Matsumura, commonly encountered on soybean and can be confused Whiteflies are most commonly seen on velvetleaf or button Geocoris are predatory is a small, pear-shaped with the soybean aphid is the cotton aphid, Aphis gossypii weed, and soybean fields with heavy weed populations aren’t keeping up with theinsects. aphids.”Nymphs are bright green to yellow (Fig. 1A). The cotton aphid, alsoAND called the melon aphid, may have higher whitefly numbers. First instars (crawlers) Cullen reports very low fall trap captures predominately silver-gray aphid with dark tips on has a broader cauda compared with the soybean aphid (A) are legged and oval shaped, about 0.3 by 0.15 mm. The with black markings and the cornicles (two (Fig. 1B), has two pairs of strongly curved setae (soybean second, third and fourth instars are also oval, do not have have a wide head and tube-like structures or aphid has 4-5) and fived segmented antennae. Cotton legs, and are slightly larger than the first instar. The late prominent bulging, “tailpipes” on the tip of aphids are usually yellow or yellow-green when on cotton fourth instar (pupa) (B) is about 0.7 by 0.4 mm and Martin Spellman widely-spaced eyes. They Jack Kelly Clark, University of California the abdomen); the cauda and soybean, but they can be light green mottled with dark appears waxy and is tightly attached to the leaf with in 2007. “We have seven suction traps are fast moving and can be or tail end of the abdomen is pale and narrow with four or green, and even dark green, especially when on melons. marginal filaments (tiny hair-like structures around the seen feeding on thrips, moth five pairs of setae, or hair-like structures. This aphid can Cornicles are all pale (cotton) or all dark (melons). entire outer edge). Coloration may vary. eggs, and small caterpillars. be found on growing points and young leavesversity of early or A B vegative soybean plants. As soybean plants mature from Fig. 1 - Caudal segment and lateFor vegatative more information, through reproductive contact your stages, county aphids extension are cornicles of the cotton aphid Lygus lineolaris office or state/provincial land-grant uni (A), and soybean aphid (B). in Wisconsin, and we captured only 11 found on all plantgovernment parts. Althoughentomology most specialist: common on Tarnished Plant Bug, undersides of leaves, theyEileen also Cullenoccur on stems, petioles Drawing by Angelika P. Schmid-Riley, 2008 looks like a light year for aphids courtesy of the University of Georgia, College and upper leaf surfaces. Soybean aphid damages plants Nymphs are about 1-5 mm University of Wisconsin of Agricultural & Environmental Sciences. by sucking phloem (plant sap) resulting in plant stunting, long, are wingless and Entomology Department reduced pod set, and smaller seed size. If populations are Marlin E. Rice, Iowa State University Jim Kalisch, University of Nebraska yellow-green, darkening and 1630 Linden Drive There are several other soft-bodied insects that can occur on large, feeding may cause shiny, sticky leaves coated with winged soybean aphids in September and developing wing pads as they Madison, WI 53706 soybean that may resemble the soybean aphid. CAUTION aphid exudate (”honey dew”)Tel: (608) and 261-1507black “sooty” mold should be taken not to misidentify these, as false positives mature. The third through Mealybug According to the suction trap network, fungal growth on soybeanFax: leaves. (608) 262-3322 may result in costly unnecessary insecticide applications. fifth instars have black dorsal Mealybugs are closely spots and are fast moving. [email protected] Thrips Species Ho Jung Yoo, Purdue University related and look similar Thrips are rarely a significant pest of soybean but often occur Scott Bauer, USDA-ARS Refer to the picture for A to whiteflies. They are October,” she says. at the same time in the field with the soybean aphid. Adult distinctive features of a C oval shaped and are and larval thrips have slender, cigar-shaped bodies. Both record low numbers of soybean aphids headedsoybean aphid. (A) covered with waxy, stages are active crawlers. Adults (A) have feathery wings, can black tipped cornicles, white, mealy secretions. be yellow, dark colored or strongly banded. Larvae (B) are (B) six legs, and (C) six Like whiteflies, they Tetranychus urticae versity of Wisconsin), wingless and usually pale to yellowish in color. Their feeding segmented antennae. B also have an active Authors: Ames Herbert (Virginia Tech), Sean Malone causes a faint striping and silvery appearance to soybean Lyle Buss, University of Florida Make certain that your crawler stage and an Twospotted Spider Mite, (Virginia Tech), Eileen Cullen (Uni leaves. pest identification is Robert Venette, USDA Forest Service Illinois) inactive stage. Although not common, they can occur back to buckthorn (where aphidsLarvae have six legs; lay eggs and Susan Ratcliffe (University of Illinois). correct before making any insecticide application. on soybean leaves and stems, but are not known to nymphs and adults have cause significant damage. eight. Adults are about A B Graphic Designer: Scott D. Martin (University of The every other year pattern 0.3-0.4 mm long. Color is This image Potato Leafhopper, Empoasca fabae greenish-yellow to dull C orange with a large dark Marlin E. Rice, Iowa State Universityshows severalThis guide was produced and distributed in cooperationricultural Don Steinkraus, University of Arkansas Michele Roy and overwinter) in the fall of 2007. Quebec Ministry of Agriculture Nymphs are 2-3 mm forms of soybean Orius Species spot on each side of the with USDA Cooperative State Research, Education, and long, wedge-shaped, aphid - the body. They are especially Extension Service (CSREES), Risk ManagementersityD Agency,System,Orius are predatory insects. Nymphs (immatures) are pale in color, and common during periods of normal green AnimalA and Plant Health Inspection Service, Ag B shiny yellow to amber colored with a pear-shaped body wingless. Older For the most part, researchers report an hot, dry weather and are form (A), a darkerResearch Service, Regional IPM Centers, National Plant Martin Spellman, University of Delaware with red eyes and no wings, and are active crawlers often nymphs are bright usually first seen along field form (B), shedDia gnostic Network, the Land-Grant Univ oductionMartin systems. Spellman (S-1010)seen feeding on aphids. green, with prominent exoskeletons (C), edges. Initial damage SDC329: Biology, impact, and management of soybean eyes and have wing appears as stippling on the and “mummies” of parasitized aphids (D) (aphids can insect pests in soybean pr pads. Unlike aphids, Marlin E. Rice, Iowa State University underside of leaves. be parasitized by small wasps that develop inside the State Sept.-Oct. Sept.-Oct. nymphs move sideways rapidly when disturbed. aphid body and exit leaving a hollow outer shell called a “every other year” situation with aphid Extreme webbing and Whitney Cranshaw, Colorado State University defoilation can occur if mummy). outbreaks. “I think what happens is when (# sites) 2006 populations are large. 2007 John Obermeyer, Purdue University Jonathan Lundgren, USDA-ARS aphids numbers are high, the predators WI (7) 213 11 A new publication helps notice, just like we do,” says Bob O’Neil, MN (5) 376 104 farmers identify soybean aphids Purdue University entomologist. “The and similar-looking insects. IL (9) 1762 9 Asian lady beetles come into soybean fields Identification of Soybean Aphids and hammer aphids. So the high numbers IA (4) 532 5 and Look-Alike Species was become low numbers for the fall flight. And IN (6) 8322 59 written by Ames Herbert, Sean next year, there aren’t as many aphids, so MI (5) 209 156 Malone, Eileen Cullen and Susan the predators don’t notice and don’t attack, Ratcliffe. Contact your Extension allowing aphid numbers to build up again. Numbers in the table show total soybean soybean entomologist for a free “That’s the hypothesis, that the pattern aphids captured from all sites per state. The copy, or download from the is associated with predation late in the data summarized are from the suction trap NCIPM Web site: www.ncipm. season,” O’Neil adds. “The alternative is network Web site: www.ncipm.org/traps. org/alerts/soybeanaphidid.cfm.

8 9 Aphid-resistant varieties are on the way Not a silver bullet – a good management tool

Checkoff-funded researchers throughout Aphid biotypes the North Central region have been testing “In general, there’s definitely a big difference new genetic sources of aphid resistance, between lines bred for resistance and the and the results look promising. susceptible control varieties,” Tilmon says. “We’re screening different lines from Unfortunately, there’s a catch: aphid biotypes several university breeding programs,” that can break host plant resistance. says Kelley Tilmon, South Dakota State Scientists already have identified one new University entomologist. aphid biotype – called biotype 1 – with “We test them on small plots in some ability to overcome the source of multiple states, with varying growing resistance known as Rag1. “We captured conditions and varying levels of aphids, biotype 1 in 2006, but there weren’t a lot and monitor aphid population growth of reports in 2007,” says Glen Hartman, and yield on the different lines. That’s the University of Illinois/USDA-ARS what we call Tier 1 screening,” she researcher who co-discovered the Rag1 says. If a line looks good in Tier 1, and other sources of resistance with it moves to Tier 2 testing, which involves another UI researcher, Curt Hill. “What larger plots and insecticides – basically we don’t know is how predominant biotype mimicking how growers raise soybeans. 1 is, or how widely dispersed it is.”

Resistance: antibiosis, antixenosis and tolerance “There are three forms of resistance,” The third type of resistance is says Matt O’Neal, Iowa State University tolerance. “In this situation, the plant entomologist. “Antixenosis is a fancy Latin can have a lot of aphids feeding on it, term that means the insect doesn’t attach but you won’t see a yield decrease,” itself to the plant. The aphid may not O’Neal adds. recognize the plant, or sometimes it might be that the plant has very hairy leaves.” According to Dechun Wang, plant breeder at Michigan State University, “If you give aphids a no-choice test, where they must feed on a soybean plant This photo shows susceptible vs. with antixenosis resistance or starve, resistant plant lines. Plants and they can still survive. For unknown plots are under a severe aphid reasons, they don’t like to feed on those infestation. plants. If there’s another plant available, aphids will move on.” Antibiosis is the second form of resistance. “Aphids may feed, but somehow feeding interferes with aphid reproduction,” says Wang. “We don’t know the mechanism causing it.”

Courtesy of Roy Scott, SDSU Courtesy of Roy Courtesy of Curt Hill, U of Ill.

10 11 Courtesy of Dechun Wang, MSU These pictures show the difference between Tweaking the E06902 (top photo), an aphid-resistant variety and Skylla (aphid susceptible) in a 250 treatment no-choice test. Each variety was individually threshold? caged, and photos were taken four weeks Now that North Central after inoculating 5-10 aphids on each plant. Soybean Research Program E06902 was released as an aphid-resistant scientists have confirmed the germplasm in 2007. 250 aphid treatment threshold and published their findings, they’re considering some fine-tuning. Tilmon says, “In most of our trials, those “Will we need to adjust lines with the Rag1 gene performed well. thresholds to incorporate the The wild card will be the aphid biotypes new aphid-resistant varieties?” that can overcome the resistance and how asks Matt O’Neal, Iowa State quickly they can evolve or spread. So now University entomologist. we have to consider how that will affect “What about the release of management in various states.” Binodoxys communis? According to Dechun Wang, a plant “If there’s one field at R1 breeder at Michigan State University, “We background will be more difficult for and one at R6 when aphids don’t know how many biotypes there are aphids to find a way around. reach threshold, would they in the United States, but we know there are “This was the first year we looked both experience the same yield differences in aphids in different locations.” at Dechun’s lines,” says Matt O’Neal, loss?” he wonders. “Later in the He doubts that aphids have already managed entomologist at Iowa State University who season, the aphids’ impact is to overcome resistance, “since we haven’t had is leading the host plant resistance project. reduced.” O’Neal experienced a resistant variety available commercially yet.” “Central Iowa was hit hard with aphids this firsthand in 2007. in 2007, and his lines looked remarkable. “We sprayed an insecticide Many sources of resistance There was one case in Wisconsin where one at the 250 threshold in July. Nature’s ability to overcome resistance of his lines didn’t do very well – and that Then aphid populations reached eventually, however, is one reason researchers may be due to aphid biotypes.” threshold again in mid-August. have so many different sources in the pipeline. So we sprayed some acreage “The Rag1 source may be available in One more tool in your toolbox again, and left some with one commercial seed in 2008, and there’s a lot O’Neal adds that, even with aphid biotypes application. In terms of yield, more material to look at,” says Hartman. that can overcome some sources of resistance, we couldn’t see a difference. “We have material transfer agreements it’s not a total loss. What this means is that We need to explore that further, with several companies for the Rag1 and resistance is going to be a good tool for but it does suggest that later- another resistance source,” Hartman adds. soybean aphid management, but not the stage beans are more tolerant, “We have about 50 different PIs (plant only tool. and it may take more aphids to introductions) that look very different from “Scout and consider an insecticide reduce yield. the Rag1 and other known sources. We if aphid populations go above the 250 “Another thing we need need to do genetic tests on them, and that threshold, even on resistant plants,” O’Neal to look at is 15-inch and 7-inch will take a couple years.” continues. “The frequency of spraying will row spacing,” O’Neal adds. Breeder Bill Schapaugh from Kansas State drop, and growers will be able to use less “That’s not to say the threshold University also has lines in testing, including insecticide. But you can’t just plant aphid- isn’t valid. We’re just checking one – K1639 – that is resistant to aphids and resistant soybeans and walk away. on fine-tuning it.” soybean cyst nematode. “That will be a good “You don’t want only one hammer for germplasm line,” Schapaugh says, “because it aphids, you want a lot of hammers,” he also has decent agronomic traits.” says. “That’s why we’re working on different Michigan State’s Wang has new resistance sources, and why we released sources of resistance in the trials as well. Binodoxys communis. Maybe if we have One source, E06902, is already being several aphid-resistant soybean varieties crossed with commercial germplasm by available, we can lower the number of aphid Syngenta. “Our studies show that E06902 migration events. If fewer aphids are flying has two two recessive genes controlling in, maybe Asian lady beetles and other aphid resistance,” says Wang. Sources of predators can catch up, and the resistance resistance with more complicated genetic can hang in there.”

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