University of Illinois

No. 3/April 10, 1998

Hatch of Alfalfa Weevils Should Be Under Way
in Southern Third of Illinois

Information provided by Bob Scott, Illinois State Water Survey, indicates that the hatch of alfalfa weevils should be well under way in the southern one-third of the state. The egg hatch of weevils typically begins whenever 200 heat units accumulate from January 1 (base 48 degrees F). As of April 6, counties in the extreme southern tip of Illinois had accumulated about 280 heat units (Figure 1). This suggests that growers should begin in earnest toscout their fields for early signs of injury very soon. As Kevin Steffey indicated in his article last week, an early peak of third-stage larvae from overwintering eggs occurs after an accumulation of 325 heat units; a second major peak of third-stage larvae from spring-deposited eggs occurs after an accumulation of 575 heat units. Consider a quick read-through of the article published in last week's Bulletin for a review of scouting procedures for this insect pest of alfalfa. Also, please let us know when you begin to noticefeeding activity from weevils this spring.

Figure 1. Actual heat-unit accumulation (base 48 degrees F) January 1 to April 6, 1998.

Alfalfa weevil injury.

Alflafa weevil adult.
Mike Gray (, Extension Entomology, (217)333-6652