SEE Mail Issue 010828 (August 28, 2001)

	Extension Entomology Mail Mike Catangui, Ph.D. Associate Professor & Extension Entomologist
August 28, 2001 (Issue 010828)

Soybean Aphid Found in Brookings ---
May Not Affect Soybean Yield This Year

Updated: Aug 31, Sept 5, Sept 28, 2001

(Click on thumbnail for a bigger picture)

This morning at around 10:30 (8-28-01), I inspected several fields of soybean near Brookings, SD
to look for soybean aphids. Within one minute, I found soybean aphids in the first field that
I surveyed. However, I did not see any more aphids in the nine other fields that I visited.

I was in each field for about 20 minutes. Infestation in Field-1 was less than one aphid per leaf.
However, some viviparous adults were already producing young aphids as in the picture above.

The leaves of soybean plants in most areas were already senescing so I am of the opinion
that soybean aphids will not cause any damage this season.

Well, looks like we have the soybean aphid now in our state. We will prepare to manage this
insect in 2002.

Remember that both the soybean plant and the soybean aphid originated from Asia. They
are now reunited as old foes but on a different arena. We will see whether the soybean plant
still knows how to defend itself from the aphid after many breeding modifications here in the
U.S.

The Asian lady beetle that started showing up in several SD counties last fall (2000), is a
natural predator of the soybean aphid. It too is of Asian origin.

Curt Reese, Research Associate with the SDSU Soybean Breeding Project, brought 2 soybean
leaves infested with adults and nymphs of the soybean aphid. The infested leaves were collected
from the SDSU Research Station near Aurora (Brookings County). Curt actually collected the
aphids on Friday (8-24-01), but did not show the aphids to me until today (8-31-01). So far,
only Brookings County has reported the presence of the soybean aphid. All soybean growing
counties are encouraged to inspect the fields before all the leaves senesce this season. That
way we could document the spread of the soybean aphid in our state.

Also today, I went back to the original site where I first found the soybean aphids and was
surprised that workers of a local ant species (Formica neogagates Emery) were already
tending the soybean aphids!

I knew it, these shameless ants will do anything for honeydew! This is the very first time
that these interspecific paramours have met and they looked like they were already
inseparable symbiotic animals. Yes indeed, anything for honeydew.

Formica neogagates is a well known honeydew drinker. It has been observed tending several
species of aphids on grass roots and bull thistles. It also feeds on sunflower exudates.
Several species of larger ants (Formica rubicunda and F. obtusopilosa) are known to
enslave F. neogagates workers. Very interesting how nature works.

For further reading:

Catangui, et al. 1996. Abundance, diversity, and spatial distribution of ants (Hymenoptera:
Formicidae) on mixed-grass rangelands treated with diflubenzuron. Environmental Entomology
25(4): 757-766.

Wheeler and Wheeler. 1963. The ants of North Dakota. University of North Dakota Press,
Grand Forks.

Wheeler and Wheeler. 1987. A checklist of the ants of South Dakota. Prairie Naturalist 19:
199-208.

I went to Moody County today to visit our bean leaf beetle insecticide trial plots. Less than
a mile east of our plots along 225th street is a soybean field in front of a church (Lutheran).
That was where I collected several leaves of soybean infested with the soybean aphid.
The aphid numbers were very low (less than 1 per leaf) like the infestation seen in Brookings
County on August 28.

Once again, before we forecast gloom and doom, be reminded that the soybean plant and the
soybean aphid may have coevolved in Asia. Coevolution is an interesting concept that may mean
that the soybean plant may have the innate capability to handle the soybean aphid. I hope that
we have not altered the soybean plant too much in our quest for desirable traits.

Pardon my Shakespeare but buckthorns, too, are a host of the soybean aphid in SD.

I was in Dell Rapids this morning at around 9:30 (9-28-01) on my daily commute from Sioux
Falls to Brookings. Dell Rapids has a lot of dells and hills so I thought I would look for some
buckthorns and perhaps, if I were lucky, some soybean aphids too. I was not disappointed.

Most of the soybeans were close to being harvested. Leaves were almost all dropped to the
ground but some plants on the very edges of some fields were still green. I saw a lot of bean
leaf beetles on these green soybean plants.

Across the road from the infested field was a shelterbelt with buckthorns (Rhamnus cathartica).
If buckthorns were indeed the overwintering host of soybean aphids, then there should already
be migration at this time here in SD because the cold weather is already setting in.

Well, sure enough, I did see some "alate" (fancy word for "winged") soybean aphids underneath
some of the buckthorn leaves. The alate aphids were also giving birth to some young aphids.
I think these young aphids will become the so-called "oviparae" or "egg-layers" that will lay
the eggs on buckthorn twigs and branches. These eggs will then be the overwintering stage.
The other aphid forms will die off as the temperature plummets below the freezing point.

Not all aphids on buckthorn at this time will be soybean aphids. The buckthorn aphid are
also present in some buckthorn plants. Aphis nasturtii is the scientific name of the buckthorn
aphid. It is an old pest of potato but is not known to infest legumes like soybeans.

Yesterday (9-27-01), I inspected some buckthorns close to the SDSU football field here in Brookings
and saw another species of winged aphid. I assume that these are the winged form of the buckthorn
aphid. I did not see any soybean aphids (Aphis glycines) in these SDSU buckthorns at this time.

I thank Dr. Gary Larson for teaching me how to identify the common buckthorn (Rhamnus cathartica).
Gary was also kind enough to show me where the buckthorns are located on the SDSU campus.

To summarize, today (9-28-01), soybean aphids were found in Dell Rapids (Minnehaha County) both
on the leaves of soybeans and buckthorns. Soybean aphids have now been confirmed to be present
in 3 eastern SD counties: Brookings County , Moody County, and Minnehaha County.

The plot thickens as winter approaches in the plains of eastern South Dakota . . .