Soybean aphids or thrips? (U/K)
Agronomy | June 22, 2006

I have received a few calls and samples concerning the presence of soybean aphids in our soybean fields.

Several people have submitted small yellow insects thinking they might be soybean aphids. They were not. They are a bright yellow thrips. As of this writing, no sample submitted to the Insect ID lab contained soybean aphids, no samples from the 16 sentinel plots contained soybean aphid, nor have we captured any in the aphid suction trap in Princeton, KY.

It is very easy for the casual or first time observer to mistake a young soybean thrips for soybean aphid. However, once you have seen each of them they are actually very easy to tell apart.

There may be more than one type of thrips on soybeans. Thrips have two larval stages which range in size from 0.6 to 1.0 mm (0.023 to 0.039 inch) long. Larvae are white when newly hatched, then gradually turn yellow with age. The soybean thrips larvae eventually turn orange with some red pigmentation, though the body sometimes has a greenish tint due to ingested chlorophyll.

Adult thrips are 1.25 mm (0.049 inch) or less in length and have two pairs of long, narrow wings fringed with long hairs. Adult soybean thrips has a yellow body with a dark blotch on the back behind the head and two distinct cross-bands on the forewings.

Generally Note-

Aphids:

Rather teardrop shaped (skinny at the head and plump in the rear),
Have a pair of cornicals (“tail pipes”) sticking out the tail end,
If they have wings (most will not) they will be rounder, not feathery with a cellophane like appearance,
Generally do not move much or move very slowly,
Very pale to deep yellow (usually) in color.

Thrips:

Long and slim,
Do not have tail pipes, but may have some “hairs” sticking out,
If they do have wings they will be long and narrow with a feathery edge,
May scurry around on the plants,
Are yellow, orange, greenish, as young and brown or yellow with spots or bands as adults.

Go to the KY-IPM Soybean Aphid page to see a color photo of the aphid.

To see other color photos look at the national soybean aphid pest alert at:

Color photos of thrips: http://www.gaipm.org/top50/thrips.html

See soybean aphid and thrips on the same page:

By Doug Johnson, University of Kentucky