Connie’s Comments by Connie Strunk, Turner County Extension Educator/Agronomy 

May 21, 2009

As farmers are busy with spring planting, tillage, fertilizing, and weed control; extension educators, specialists, and researchers are making preparations for their upcoming field research.  I will be continuing my work with evaluating the soybean aphid resistance gene in soybeans.  Instead of being on-farm, this study has been moved to the Southeast Research Farm in Beresford, S.D. so this study can be incorporated into field schools and crop tours. 

An opportunity that is available to soybean growers in the state of South Dakota is to be part of the soybean aphid parasitoid release project.  Last year there were about 62 releases in six Midwestern states during the 2008 summer.  Turner County was one of 10 release sites in South Dakota.

Based on the Environmental Assessment Study, Binodoxys communis, soybean aphid parasitoid wasps were permitted by the USDA to be released starting in 2007.  In order to be released the parasitoids must not go off target (the target in this case are soybean aphids).  The only insects that it attacks are soybean aphids.

How big are parasitoids and do they sting?  Parasitoids are very small insects, about the size of this comma, and are biologically incapable of stinging or biting people.  Furthermore, parasitoids seldom stray far from the habitats of their host insects.  The soybean aphid parasitoid (Binodoxys communis) is about the size of a gnat and is biologically incapable of stinging or biting people.

A parasitoid reproduces by laying her egg into the aphid body. The egg hatches into a larva which feeds inside the aphid.  Eventually the larva enters a developmental stage called a pupa, as it undergoes the transformation to an adult. The aphid dies and forms a protective shell around the developing parasitoid pupa (a “mummy”). The adult exits the mummy, leaving the shell of the aphid mummy behind. 

So why is this parasitoid important?  The Binodoxys communis (soybean aphid parasitoid) is a natural enemy to the soybean aphid.  Natural enemies are predators, parasites, and diseases that prey on a pest (in this case, soybean aphids).  Predation reduces aphid numbers (slows their overall growth).  If predator numbers are high, they can help prevent aphid outbreaks (in good years).  Depending on your predator numbers and the year, you may be able to avoid treating for soybean aphids thus saving some production cost.  Insecticide use, when not needed, can knock out natural enemies, which are your first line of defense against aphid outbreaks.

So how does the Binodoxys communis work?  A parasitoid reproduces by laying her egg into the aphid body. The egg hatches into a larva which feeds inside the aphid.  Eventually the larva enters a developmental stage called a pupa, as it undergoes the transformation to an adult. The aphid dies and forms a protective shell around the developing parasitoid pupa (a “mummy”). The adult exits the mummy, leaving the shell of the aphid mummy behind.  This parasitoid is specialized to prey on soybean aphids (concentrates only on this pest) and is incapable of attacking other types of insects. 

What did we learn from the 2008 release in Turner County?  We introduced 337 parasitoid mummies the week of July 28, 2008 into cages with soybean aphids.  The numbers were allowed to build up and then the cages were removed to release the parasitoids.  We removed the cages during the week of the Turner County Fair and found between 0 and 14 mummies per plant in the cage upon removal.  We counted the 16 plants surrounding the cage borders between August 28 and September 8, 2008 and found a total of 23 mummies on the plants.

            We hope that they establish in the area and that the populations slowly grow and spread over time.  It may take several years to make these aphid-killers a permanent part of the soybean ecosystem.  If the soybean aphid parasitoids become established, they will work for free but this will not eliminate the need for soybean aphid monitoring and treatment, but may reduce the amount of treatments made.  We will do follow-up monitoring this summer to release sites made in 2008.

For additional information about this soybean aphid parasitoid release project contact Kelley Tilmon by email at Kelley.Tilmon@sdstate.edu or for more information about soybean aphid biological control visit www.entomology.wisc.edu/sabc/.  This biological opportunity is open to all soybean producers in the state of South Dakota.  

For more information please feel free to contact me at the Turner County Extension Office at (605) 297-3112.  Your help with on-farm research is greatly appreciated! 

For your information:  A Hands-on Sprayer Tune-up Clinic is scheduled for June 2, 2009 from 9:00 a.m. to noon at the Southeast Research Farm in Beresford, S. D.