Annual white grub adults are flying throughout Illinois. Adult northern masked chafer has been picked up in central Illinois, and adult southern masked chafer has been found at The Morton Arboretum in northern Illinois. Effects of the early spring are still with us, because these insects usually appear about July 2 in central Illinois and July 8 in northern Illinois. This makes them one week early in central Illinois and two weeks early in northern Illinois.
These June beetles are about 1/2 inch long and tan with black heads. They hide in the thatch during the day, emerging in the evening to mate and lay eggs. These insects do not feed, so they run out of stored food and die after about two weeks. After mating, females tunnel into the soil to lay their eggs. The resulting larvae are some of the white grubs that cause severe turf damage in the fall. Getting a rough idea of adult numbers helps one decide whether an insecticide treatment to prevent damage will be needed.
The two species are out at different hours of the night. Southern masked chafer is more active between 9 and 11 p.m., whereas northern masked chafer is more active from midnight to 4 a.m. Between 10:30 and 11:00 p.m. is a good time to check on their numbers, because some of each species will be active at that time. Shining a light, such as car headlights, across the turf will reveal them flying over the turf. They are also strongly attracted to lights at night, and can be monitored by checking porch and street lights.