Questions are surfacing about the likely timing of the annual corn rootworm larval hatch, says Mike Gray, University of Illinois Extension entomologist.

Some believe this biological event coincides with the first sightings of lightning bugs in the spring. Gray suggests that while these events may happen at the same time, they are unrelated and not a good estimate of when this hatch will occur.

Data suggests hatch may be just around the corner for central Illinois. Entomologists have estimated that approximately 50% of the corn rootworm hatch occurs when 684 to 767 degree-days (52 F) have accumulated from January 1. Last week, a quick glance of degree-days across the North Central Region indicates that 600 degree days have accumulated across central Illinois. For much of northern Illinois, roughly 400 to 450 degree days have accumulated.

Purdue University entomologists, who annually dissect corn roots looking for the first instars and so far, have not reported any hatch.

"If the hatch occurs later than predicted over the next several years, we may begin to build a body of evidence that suggests we may be selecting for corn rootworm larvae that hatch later due to the extensive use of Bt corn hybrids," Gray adds.

For more information, check out the May 20th edition of The Bulletin, an online publication written by U of I Extension specialists in crop science, at ipm.illinois.edu/bulletin.