The latest update from K-State Extension Entomology on insect activity across Kansas includes alfalfa weevils and pea/cowpea aphids. What effect, if any, has the recent cold temperatures had on these insects?
Alfalfa weevils have been, and are still, very active throughout south central and north central Kansas during the last few days, even during the cold weather. However, just as the alfalfa plants have been variously affected by the recent cold weather, so have the alfalfa weevil larvae. The plants shown towards the middle of this picture (Figure 1) had the upper part of the foliage killed by the recent cold temperatures, as were the larvae in that foliage (Figure 2). The adjacent plants were not as seriously affected and thus, neither were the larvae in those plants.
Figure 1. Alfalfa freeze damage (center portion of the photo). Photo by Cayden Wyckoff, K-State Research and Extension.
Figure 2. Dead alfalfa weevil larvae (top left) and live alfalfa weevil larvae. Photo by K-State Extension Entomology.
Therefore, each field needs to be monitored at least weekly, even those fields already treated. Please - always remember to follow all label directions for whatever product applied, especially as far as re-entry, PHI, etc.
Pea aphids/cowpea aphids
The recent cold weather also played havoc with these aphids (Figure 3). However, many aphids in untreated fields were just "knocked off" or left the plants and are still alive, but in the leaf litter or residue under the foliage. There are also lady beetle larvae feeding on these aphids, so hopefully these aphid populations won't come back as dense as they were previous to the cold weather.
Figure 3. Pea and Cowpea aphids. Photo by Cayden Wyckoff, K-State Research and Extension.
Jeff Whitworth, Extension Entomology Specialist