Insect I.D.: Jan. 2001, Pest Classification: Common White Grubs

LIFE CYCLES. The life cycles of grubs can be classified according to the time required for completion of the cycle from egg to adult, namely:

1. Less than one year
2. One year
3. Two years or more

Among those requiring two to five years to complete a cycle are some species of May beetles or “Junebugs,” often seen around lights on warm spring nights. These beetles generally are large, hard-bodied, and vary in color from tan to brown to black. Some species feed on the foliage of trees and shrubs at night, others do not feed at all. Feeding, flight, mating and egg laying occur at night.

Masked chafers, Oriental beetles, Asiatic garden beetle, European chafer and green June beetle are examples of grub species that generally complete their life cycle in one year. The common Japanese beetle is perhaps the best known example of this group.

The black turfgrass ataenius grub often has two generations per year, especially in the southern part of its range.

GRUB DIAGNOSIS. Evidence of annual white grub damage includes patches of wilted, dead or dying turf visible during spring (April and May) and fall (September to November). The black turfgrass ataenius may cause similar symptoms in late June, July or August. During these periods, the presence of the grubs is often made evident by the feeding activity of skunks and other mammals which tear up the turf in search of grubs. Large flocks of various black birds (e.g., crows, starlings, grackles) often feed on grubs in heavily infested areas.

Ground mole activity may also indicate white grub problems, though moles also feed on earthworms or other insects.

The sure way to detect white grubs is to cut into the turf in four for five locations and examine the root zone and first 3 inches of soil carefully. A standard golf course cup cutter can be used for this purpose. The sample can be examined and replaced in the hole without complete destruction. Pouring water on the replaced sample helps survival of the disturbed turf.

GRUB IDENTIFICATION. There are many species of white grubs, and identification is based primarily on the pattern of spines found on the underside of the tip of the abdomen. This area is called the raster. A 10- to 15-power hand lens is adequate for examining the rastral pattern of most white grubs. If the grubs are very small, a dissecting microscope with 20- to 40-power magnification may be needed.