Plant Health Initiative

NCSRP, along with state checkoff boards and the USDA, has invested in a huge biological control effort to keep aphid populations low. The goal is to identify how pests are controlled in their land of origin and bring those controls to our country. It’s a complicated process that takes years. A multi-state experimental release of the first natural enemy, an aphid parasitoid called Binodoxys communis, took place during the 2007 and 2008 field seasons, and more is planned for 2009 and 2010. Read more»

Soybean aphid natural enemies

Aphids are slow-moving, succulent, and generally poorly protected from predators. Therefore, they have many natural enemies. The soybean aphid is only a sporadic pest in most of it's native range in China, Japan, and Korea because of the presence of parasites and predators that keep them in check.

Even though the soybean aphid is a recently-introduced species in North America, generalist predators and aphid parasites are already present in soybean fields and have the ability to delay or prevent severe outbreaks of the soybean aphid. In a recent study in 22 locations in the North Central region, more than 50% of aphid-infested fields were kept below threshold level by predators.

Researchers are studying these natural enemies and ways to enhance their effectiveness. Growers are encouraged to recognize the contribution of natural enemies in keeping aphid populations in check.

Aphid predators are common in soybean fields

Predators are abundant and the most easily observed natural enemy of aphids in soybean fields. Common predators include

• many species of lady beetles and their larvae (especially the multicolored Asian lady beetle, Harmonia axyridis)
• the incidious flower bug, Orius insidiosus
• larvae of the syrphid fly (hover fly or flower fly)
• lacewing larvae

These common predators are good ones to know.  A new publication to help you identify beneficial insects is Biological control of insects and mites: An introduction to beneficial natural enemies and their use in pest management. University of Wisconsin Cooperative Extension Publication A3842 by UW entomologist Dan Mahr and his colleagues. It can be downloaded or ordered from the UW Extension Learning Store website. A pocket flip guide called Identifying Natural Enemies in Crops and Landscapes E-2949, is available to order or download from the Michigan State University.

Larva of the hover fly, also called flower fly or syrphid fly. Photo credit: Oregon State University	Orius insidiosus with aphid. Photo credit: Matt O'Neil	Brown lacewing larva. Photo credit: Dan Mahr

Application of broad-spectrum foliar insecticides will kill beneficial insects unnecessarily, allowing soybean aphid populations to rebound in a "natural enemy-free space" if applied too early. This is because aphids are all female during the summer and don't need to mate. The reproduction of natural enemies is much slower and requires time for mating, egg-laying, and hatch.

Aphid parasitoids are specialized and highly effective

A lesser known, but highly effective group of aphid natural enemies are the parasitic wasps. Parasitic wasps are tiny, free-living insects in the adult stage, but in the larval stage are parasitic. They are highly specialized and effective natural enemies of aphids, and their numbers are reported to be increasing in the North Central region.

The adult parasitoid lays eggs in the host, which hatch and eat their hosts from within, ultimately killing the host. Under favorable conditions, parasitoid numbers can increase rapidly and reduce aphid populations dramatically. Soybean aphid parasitoids in Asia play a large role in keeping aphid populations at non-pest status.

A parasitic wasp, Aphelinus albipodus., lays eggs in a soybean aphid.. Photo credit: University of Wisconsin	The parasitized dead aphid is called a "mummy". It looks like a puffy brown, black or tan version of the aphid. Photo credit: Dan Mahr	The larval and pupal stages occur inside the mummy, from which the new adult wasp emerges. Photo credit: Camila Botero

Entomologists in the North Central region have identified soybean aphid parasitoids as possible agents for classical biological control.The idea behind classical biological control is to explore the native range of an introduced pest and identify natural enemies for importation into the United States. Successful examples of classical biocontrol the U.S. include the introduction of parasitoids to control the cereal leaf beetle and the alfalfa weevil.

As part of an NCSRP checkoff-funded aphid biological control project, aA number of aphid parasitoids have been identified and brought back to the U.S. where they have been in quarantine. Several years of research have been conducted on the biology, safety, and non-target impacts of potential candidates. So far, Binodoxys communis, a parasitic wasp, is the most promising. It was approved for release by the US Department of Agriculture in 2007, and releases were made in summer 2007 and 2008.

Aphid pathogens can devastate aphid populations in humid weather

Insects, like plants and animals, are attacked by microorganisms that cause disease. In particular, fungal diseases can infect a high percentage of an aphid population very rapidly, resulting in significant levels of control.

Entomologists in Minnesota and in Wisconsin have found high levels of diseased aphids on soybean, especially later in the growing season. Aphids infected by fungi will have varying degrees of "fuzzy" fungal mycelial growth emerging from the dead bodies. This mycelium produces spores which are released into the environment and infect additional insects.

Foliar fungicides applied to soybean are detrimental to this group of natural enemies and unnecessary fungicide applications should be avoided to preserve these beneficial fungi.

Aphids being colonized by the entomopathogenic fungus, Paecilomyces lilacinus Photo credit: Bill Stoneman

 

Adult and larva of a ladybeetle. Photo credit: Marlin E. Rice

Resources

• Soybean Aphid Biological Control (SABC) website
• Illinois Natural History Survey : The Good Guys - Natural Enemies of Insects
• Biological Control of Insect Pests on Field Crops in Kansas (pdf)
• The publication Soybean Aphids in Iowa (pdf format) has a section and photos on aphid natural enemies.
• Identifying Natural Enemies in Field Crops. Field manual available from Michigan State University Extension
• Biological control of insects and mites: An introduction to beneficial natural enemies and their use in pest management. University of Wisconsin Cooperative Extension Publication A3842 . Mahr, D.L., Whitaker, P., Ridgway, N.M. 2008 (print copies available from the UW Learning Store).