Soybean Aphid Found In North Carolina John Van Duyn, NCSU Department of Entomology V. G. James Research and Extension Center Plymouth, NC
Soybean Aphid in NC • In September 2005 colonies of soybean aphid, Aphis glycines (SA) were found in NC soybeans by crop consultant Stan Winslow. • He first found the pest on beans in a Chesapeake, VA field in early September; this field was sprayed. • Later in September, fields with low levels of SA were found in Gates, Currituck, and Camden counties; populations never reached the treatment threshold. • However, in 2005 many Virginia fields were treated for SA in the Northern Neck and Eastern Shore regions.
Distribution of Soybean Aphid in US • SA was first discovered in MN in 2000; however, a local crop consultant claims to have seen infestations in 1999. • That same year it was also found in Wisconsin, Michigan, Indiana, and Iowa. • Since that time it has spread very rapidly and is now found in all major soybean growing states, as far south as Mississippi and Georgia. Figure 1 shows 2005 distribution of soybean aphid.
Distribution of Soybean Aphid in Asia • SA is widely distributed in eastern Asia (China, Japan, and Southeast Asia to Malaysia and Indonesia). • It has been introduced into Australia. • This wide distribution, from temperate to tropical environments, indicates that it can adapt to most regions of the US. • However, the SA introduced into the US appears to have come from northern latitudes since it uses an alternate host on which to over winter as eggs -- a behavior common to aphids adapted to cold climates.
Identification of Soybean Aphid • SA is a close relative of the cotton aphid, which is commonly found in NC and is familiar to many farmers. • SA is the only aphid found in the US that will develop large colonies on soybean plants. • Adult soybean aphids are generally yellow, have black cornicles (cornicles are tail pipe looking structures at the back of the body), and are approximately 1/16 of an inch long when fully grown. • Young aphids look like adults without wings but are smaller. • Adult aphids may be wingless, or, during periods when they move, develop wings.
Soybean Aphid Biology • Eggs hatch in spring to produce winged females. • Early season SA don/t mate and move on winds. • They move to soybean fields and begin laying living young (not eggs). • New aphids are sexually mature in 3-7 days and new progeny will begin reproducing in 5 days. • SA may infest “V” stage soybeans and remain in the crop into the late reproductive period. • Later in the season males appear, due to plant chemical and photoperiod changes, develop wings, mate with females and move. • Adults females lay eggs on several species of buckthorn bushes for over-wintering; southern adapted populations in Asia may be active all year.
Damage & Virus Transmission • SA sucks sap (phloem) from soybean plants and cause plant stress. • Excess sap sugars are excreted by the SA as a liquid aphid called “honeydew”. • On “V” stage plants aphids are only a threat under very high populations. • “R” stage soybeans are more sensitive to aphid damage, particularly in early reproductive stages (e.g. R1 – R3); very high numbers of SA are capable of causing significant growth reduction, distorted foliage, and lower seed yields. • Wang et al. (1996) in China found that soybean yields were reduced by 27.8% and plant height decreased by ca. 8 inches-6.
Damage & Virus Transmission • Insecticide spray tests in the US have shown yield increases ranging from 10% to 20%, depending on aphid population density, product used, and other plant stresses. • SA is a known vector of a number of plant virus diseases. • E.G., some domestic viruses spread by SA include alfalfa mosaic virus, soybean mosaic virus, and bean yellow mosaic virus.
Scouting and Thresholds • In the mid-west, scouting is achieved by examining plants for signs of aphids (e.g. disfigured leaves, ants on plants, cast aphid skins, honeydew on leaves) and aphids in plant terminals. • Scouting begins in mid-vegetative stages and continues to R5 (seeds forming in pods); it is done weekly. • Aphids are estimated on the leaves and an average of five samplings is compared to a threshold of 250 aphids per terminal leaf.
47 aphids/leaf 11 aphids/leaf 82 aphids/leaf Soybean aphids on soybean leaves at 3 below threshold levels.
Biological Control • NC entomologists recommend biological control for cotton aphid management. • The same approach will reduce populations of SA. • Parasitic wasps, insect predators, and a parasitic fungal pathogen of aphids can exert a powerful influence to keep aphids in check. • Basically, all the farmer has to do is to avoid disrupting the field, by spraying insecticides at the wrong time. • Most spraying for corn earworm and other insects occurs after plants pass the aphid sensitive stages and will likely not conflict with aphid management.
Upper – lady beetle adults and larva. Lower – dead aphids (brown puffed-up aphids) killed by a wasp parasite.
Soybean Aphid Insecticides • Soybean aphid is sensitive to a number of insecticides labeled for soybean in NC. • Several pyrethroid insecticides that are popular with farmers, for corn earworm control, will work on aphids and are labeled for aphids. • Several phosphate insecticides are also available. • Products labeled on soybean for soybean aphid control include: Asana XL, Baythroid 2, Lorsban 4E, Mustang Max, Penncap-M, and Warrior.
Will Soybean Aphid Become An Important Pest In NC Soybeans? • SA is northern-adapted and relies upon an alternate over-wintering host, the buckthorn bush. • In NC, the soybean aphid will have trouble surviving winter in substantial numbers due to the relative low number of buckthorn plants. • This suggests that SA will have to travel into NC, in high numbers, to infest vegetative stage soybeans to damage “R” beans. • This possible but unlikely, if fields are not disrupted. • Until SA adapts develops an over-wintering behavior that doesn’t require buckthorn bushes, SA will likely remain as a minor pest. • When this happens, soybean aphid on soybeans may be much like cotton aphid on cotton --- that is, a somewhat frequent pest.
Acknowledgement • Information and pictures for this presentation were gathered from the following sources: • Soybean Aphid in Iowa – 2005. by M. E. Rice and P. Pedersen, Iowa State University; (http://www.extension.iastate.edu/Publications/SP247.pdf); • Soybean Aphid in Nebraska. by Tom Hunt, University of Nebraska. (http://entomology.unl.edu/fldcrops/soybean_aphid04.htm); • Soybean Aphid. Plant Health Initiative, NCSRP (http://www.planthealth.info/diag_photo_dp.htm); • Minnesota Soybean Production, Soybean Aphid. by Ken Ostlie, University of Minnesota. (http://www.soybeans.umn.edu/crop/insects/aphid/aphid.htm) • Soybean Aphid. Center for Regulatory and Environmental Information Systems. (http://ceris.purdue.edu/napis/pests/saphid/index.html)