Wisconsin’s annual fall survey documented a decrease in the state average European corn borer population from 0.40 in 2005 to 0.29 borer per plant in 2006 (29 borers per 100 plants). This compares to a 10-year average of 0.30 and a 50-year average of 0.48 borer per plant. The northwest, west central, and central districts showed increases from 0.01 to 0.27, 0.24 to 0.42, and 0.44 to 0.51 borer per plant, respectively. The largest decreases in 2006 were documented in the south central and southwest districts, where averages declined from 0.67 to 0.38 and 0.49 to 0.20 borer per plant. Lower densities in the southern districts may be associated with increased planting of Bt corn hybrids, although no specific evidence for this hypothesis is available at this time. Testing of field corn for transgenic traits during the summer corn rootworm beetle survey showed the highest utilization of hybrids in the southern three tiers of Wisconsin counties (see map in Corn Rootworm section).