Just a quick update on the field situation. In general, soybean aphid populations are behaving in the region as they have in normal years . . . currently low populations well below threshold. A few reports of increasing numbers, maybe even a few justifiable treatments in smaller fields where there is significant, wooded habitat nearby.

It is time to begin scouting more earnestly as we approach the time when populations in normal years begin to increase.

Field Cages: How they may
influence soybean aphid populations

Here is an excellent example of the importance of predation in delaying the development of soybean aphid populations.

About 4 weeks ago, a 3' x 8' cage was placed in a soybean field near Fergus Falls, MN (actually just to test the screening materials of the cage prototype, not to gather aphid population data).

When it was placed into the field, there were ~10 aphids in the entire caged area (far fewer than 1/plant). Since then, aphids in the surrounding field have become slightly more numerous . . . plants averaged ~1.8 aphids/plant. Inside the cage, however, plants averaged ~780 aphids/plant.

The cage excluded predators and parasitoids while those outside the cage were exposed to these mortality factors. Several different predators, including lacewings and ladybugs, were noted in the field when the cage was placed; populations of these predators were greater now. The difference was truly striking (a statistics professor of mine used to refer to these situations as inter-ocular hypotheses - the difference is so great it hits you between the eyes!)

In figure 1, the top picture is of a plant stem from inside the cage, where plants averaged ~780 aphids/plant. The bottom image is of a plant growing outside the cage (from a row immediately adjacent to the cage); plants outside the cage had ~1.8 aphids/plant (note no aphids are clearly visible on the stem or leaves). Inside the cage, cast skins and honeydew were quite common on the leaf surfaces; plants outside the cage had no such evidence of aphid presence.

At this site, it was the same colonizing population, but with very different population development. Bottom line, natural enemies are having a significant impact on the establishment and development of soybean aphid populations. Give them a chance to work at low populations; looks like they're doing a great job here....

Ian MacRae, Extension Entomologist
NWROC, Crookston