Japanese beetles are spotty throughout central and northern Illinois--high numbers in some areas, much lower in others. In northern Illinois there are some areas of low populations where there were heavy numbers last year. Possibly there are more beetles yet to come, but the combination of the calendar and the earliness of other occurrences makes it likely that most of the emergence is over. In central Illinois, Japanese beetles are quite numerous in some areas, but feeding is already starting to decline. Typically, these beetles are present for about six weeks.
Earwigs continue to be very numerous. They have been reported in Knox County, a new area for them. High numbers are reported in Lake County, LaSalle, Peoria, and Rockford. These insects appeared first in high numbers in Rockford three to four years ago. Usually, earwigs are very numerous for the first four years or so in a new area, then their numbers decrease. From these data, it appears that the earwigs are moving progressively west through the state. Most of the Chicago area first had heavy numbers in the 1980s.
Mimosa webworm will be entering the second generation throughout most of the state, so keep an eye on honey locust trees. Second-generation moths tend to lay their eggs into first-generation damage, so check for new, young larvae in areas with brown leaflets webbed together. This second generation will web together three to four compound leaves and feed on them, turning them brown. Scouting at this time and treating where needed will prevent heavy damage from occurring later.
White-marked tussock moth, yellow-necked caterpillar, walnut caterpillar, and other caterpillars are commonly numerous on deciduous trees at this time of the season. A whitish leaf may indicate a developing infestation. The moths of many caterpillars lay their eggs in clusters. The hatching caterpillars feed on the lower leaf surface and leaf interior, leaving the upper surface intact. This upper surface is whitish and is easily noticed. Close inspection is likely to reveal many small caterpillars. Ignored, these caterpillars are likely to eat all the leaves of two or more large branches. Although this damage is not life-threatening to a healthy tree, it does cause considerable aesthetic damage. Control at this stage is as easy as plucking the infested leaf and dropping it on the ground several feet away from the tree.