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Angie Peltier


Angie Peltier
Former Extension Educator, Commercial Agriculture



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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Soybean aphid eggs are shiny and black and can be found near leaf buds on buckthorn plants (arrows) (Image: Michael Crossley).
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The soybean aphid: Many mysteries still remain

Posted by Angie Peltier - Insects

University of Wisconsin Entomology Professor Dr. Dave Hogg and an undergraduate student (Tom Olson) traveled to the Blackhawk Nature Preserve in Rock Island, Illinois to collect winged aphids for identification and genetic analysis (Figure).

 

What Researchers have Learned about the Soybean Aphid Life Cycle. The soybean aphid (Aphis glycines) has a very unique life cycle. In the spring, aphids hatch as nymphs (small versions of adult aphids) from eggs and go through several molts until they reach adulthood (Figure). With each molt, the nymphs grow larger and leave behind small, white shells of their former body covering on a leaf surface (Figure). Throughout their life cycle, soybean aphids use small piercing, sucking mouthparts to extract sap from soybean tissue. In large populations the soybean aphid can cause severe stunting and deformed soybean leaves resulting in significant yield loss.

Aphid adults are initially all female and reproduce asexually through a process called parthenogenesis by which females can give live birth to female nymph 'daughters' that are clones of the mother. Sometimes daughter aphids are born pregnant. Aphid growth and development is temperature-dependent and under optimal conditions aphids can go to birth to reproduction in 5 days.

Soybean aphids feed and reproduce asexually on soybean plants throughout the growing season until day-length cues stimulate the birth of winged, pre-sexual females called gynoparae or reproductive males. These winged females then fly to buckthorn plants.

Buckthorn plants are woody, deciduous, perennial shrubs that were historically planted as windbreaks or ornamental shrubs. Some buckthorn species (Rhamnus alnifolia and carolinia) are native to North America, however the soybean aphid tends to travel to the more abundant buckthorn species native to Europe. Common buckthorn (Rhamnus cathartica) plants are very prolific and can often be found near forest edge communities.

Aphid gynoparae travel to buckthorn in late summer and early fall where they live and feed for 7 to 10 days and then give birth to nymphs of reproductive wing-less females called oviparae. After sexual reproduction, oviparae lay microscopic, shiny, jet-black egg masses near buckthorn leaf buds.

The following spring, aphid egg hatch coincides with the emergence of buckthorn leaves from leaf buds. Newly hatched aphid nymphs feed and develop into adult females which asexually reproduce on new buckthorn leaves (Figure). At some point during the spring, winged female aphids leave buckthorn and move to soybean fields. Soybean aphids can complete multiple generations while living and feeding on soybean plants.

 

Unknown Aspects of the Soybean Aphid. There was a reason that the Wisconsin team traveled 2 ½ hours from the University of Wisconsin in Madison to the Quad Cities. Although the soybean aphid is a pest of soybean throughout the entire Midwestern region of the U.S., aphids do not overwinter in Wisconsin. They tend to congregate along the Interstate 80 corridor from the Quad Cities in the West to Cleveland, Ohio in the East. Dr. Hogg's team and other university entomologists throughout the Midwest are working hard to determine just why they do this.

To better understand both the life cycle and the genetic diversity of the soybean aphid in the Midwest, Dr. Hogg's team collects winged aphids from buckthorn leaves to bring back to Wisconsin. The team then identifies the aphids as either soybean aphids or some other aphid in one of three ways:

1) A bioassay in which they move a winged aphid onto a soybean plant in a cage and determine whether it can live and reproduce

2) Preserve the winged aphids in alcohol and use specific identifying body parts to later identify them under a microscope

3) Extract genetic material from the winged aphid and run a genetic analysis

During the growing season, many field research sites throughout the Midwest use suction traps to capture winged soybean aphids in flight. This trap count data can be used to determine whether large numbers of soybean aphids are in flight during the fall (during mating) and there is the potential for a large overwintering egg population or whether aphids are in flight during the spring and summer and pose a risk to soybean fields.

Soybean aphids have not reached economic threshold levels (250 aphids/plant) in recent years due to a combination of unfavorable weather conditions and natural predator populations. However soybean entomologists and producers remain vigilant to the potential threat of this destructive pest.

 

More Information. More information about the soybean aphid, scouting practices and economic thresholds can be found online. Here are different online resources that have been developed from multiple funding sources: grain sales check-offs (Iowa Soybean Association and the North Central Soybean Research Program) and federal funds (North Central IPM Center).

Soybean Aphid Field Guide

Speed Scouting Card for Soybean Aphids

Soybean Aphid Research Update

Aphid Basics

 

 



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