Thursday, June 13, 2013

Aphids in corn?!

I saw something new for the first time today - aphids on V4 corn. Actually, my summer crew found them while scouting for early-season pest activity in a small plot trial at the ISU Johnson Farm just south of Ames, Iowa. Nice job scouting today - way to go!

Meet part of the 2013 crew. I hope to post something just about our lab personnel soon. 

This find is exceptional for three reasons. First, Iowa corn doesn't always get infested with grain aphids. The overwintering potential in Iowa isn't fully understood, but most people think they have to migrate here from the southern U.S. every year (kinda like potato leafhopper and many other insects). So it can be hit or miss if they land here and establish at all. But grain aphids would rather live on small grains, like wheat sorghum, barely, oats, rye, etc. However, some of these aphids will feed on corn and have been known to build up to extremely high populations after tasseling. There was an corn aphid outbreak in much of northern Iowa in 2011. But finding them in mid-June is very interesting (to an entomologist!).

The second curious part of finding aphids in corn this early is that all conventional corn contains an insecticidal seed treatment. My general thinking is aphids shouldn't like to feed on that or stick around long enough to produce nymphs. But it wasn't hard to find alates (winged adults) and nymphs in this small plot trial.

While looking for cutworms and stalk borers, we found aphids instead!

Alates and first instars were easy to find on V4 corn today. 

 The alate was gone, but left behind at least four nymphs on this plant. 

The third thing that was surprising is I identified them as English grain aphids. Of the many species we can potentially find in Iowa, the two most common species are corn leaf aphid and bird cherry oat aphid. English grains aphids are a little larger than either of them, but not as big as a pea aphid. Adults have dark cornicles (tailpipes on the sides of the abdomen), "knees," and "feet" with a pale cauda (little appendage at the very tip of the abdomen). This species does not alternate between a primary, woody host and secondary perennial host (like with soybean aphid). It is capable of vectoring barley yellow dwarf virus in small grains. It can overwintering on true grasses within the Poaceae family. 

English grain aphid, note the dark knees and feet. Photo by Rothamsted Insect Survey.

I should note we didn't see large colonies on any plant. The alates are migrating to these plots and dropping off a few nymphs. We don't know if they will survive or succumb to the insecticidal seed treatment. Of course we are monitoring these plots weekly and I will post an update if they survive. But in general it means that aphids are around in central Iowa. If colonies persist and are allowed to develop over the growing season, it could be significant feeding that results in yield loss. 

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