Alfalfa weevils have been active throughout Kansas for about 3-4 weeks. Alfalfa weevils are usually the first pest causing serious damage in the spring. However, every year is different as to when this damage starts based upon the temperatures in the fall and winter when the eggs are actually deposited and start developing. Eggs may be deposited and continue to develop anytime temperatures are over about 45°F. Thus, eggs may continue to hatch in the spring for 4-6 more weeks, depending upon when they were deposited in the stems. Larvae then feed anytime the temperature is between 40-80 °F, slowing down below or above those temperatures. But it takes temperatures in the lower 20°F range for a couple of hours to actually kill alfalfa weevil larvae.
Pictured here is a 10-day-old larva (about ¾ grown) plus a couple about 3 days old, and a very small one that just hatched, with the characteristic leaf feeding (Figure 1). Alfalfa weevil monitoring should continue until the first cutting.
Figure 1. 10-day-old alfalfa weevil larva (1); two 3-day-old larvae (2); and a larva that just hatched (3). Photo by Department of Entomology, K-State Research and Extension.
Jeff Whitworth, Extension Entomology Specialist
jwhitwor@ksu.edu