Green June Beetle
11 July 2006
Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580 fax: 434.872.4578
Summer is the time when we are visited by a variety of scarab beetles. Scarabs come in a wide variety of colors and sizes. Most scarabs are beneficial but some are not so. It is those in the latter category that we are often most concerned about. Whether it is the infamous Japanese beetles or the brown or green June bugs, these beetles of the Family Scarabaeidae are now flying about looking for mates and feasting on our ornamentals and fruit trees.
One of the largest of these troublesome beetles is the green June beetle, Cotinis nitida. Despite the name, these beetles may be seen anytime from June until August. The adults are large, thick-bodied, somewhat flattened, green beetles that have a green metallic shine with bronze edges. They are almost 25 mm long (1 inch) and about half as wide. The green June beetles fly during the day and should not be confused with the brown June beetles that we see crashing into our porch lights at night during this same time of year.
Scarabs go through complete metamorphosis in their life cycle starting with eggs and on through larval, pupal and adult stages. Green June beetles overwinter as grubs commonly called white grubs, 20 to 60 cm (8 to 24 inches) deep in the soil. In the spring the grubs burrow close to the surface where they tunnel on their backs, despite the existence of six functional legs, and feed on decaying organic matter. By burrowing, tunneling, and some actual feeding, grubs injure the roots of grasses, vegetable and ornamental plants, and seedlings in plant beds. Following a heavy rain or at night, they may come out of the soil, piling soil around the burrowing opening. There are three instars or larval stages with body lengths of 1/4", 3/4", and 2" respectively and in mid-spring the grubs pupate in hollowed-out, earthen cells in the ground about 20 cm (8 inches) below the surface. Pupae more or less resemble the adult beetles in size and shape. Although white when first formed, the pupae gradually darken to green before the adults emerge. Adults begin to emerge in June and are most abundant in July and August. Adult beetles feed on foliage and fruit of trees, shrubs, and fruit crops such as peaches and grapes. Female adults will lay their small, white, spherical eggs about 7 or 8 cm (3 inches) deep in soils high in decaying organic matter. Eight to twenty days later, the eggs hatch and the young grubs burrow and feed on the decaying organic matter until cold weather arrives.
In small numbers these grubs can be beneficial. They help the decomposition process of organic material into more plant available forms, they aerate your soil, and they are food for your birds no charge except room and board.
If populations grow large enough there could be trouble for your turf. The damage in turf from white grubs may first appear to be drought stress. Heavily infested turf looks off color, gray-green, and wilts rapidly in the hot sun. Continued feeding will cause the turf to die in large irregular patches. The tunneling of the larvae cause the turf to feel spongy under foot and the turf can often be rolled back like a loose carpet. Grub populations may not cause observable turf injury but you may find you have a lot of skunks, raccoons, opossums, and moles digging in the turf in search of a meal.
As a rule white grubs need water for eggs to hatch. Most years in central Virginia we have a dry spell about mid-summer and the population is limited by the lack of moisture. If we stay wet in July and into August it is likely that populations of these beetles will reach troublesome levels this fall and into next year. If a dry spell occurs and you do not irrigate your lawn they will suffer. Fortunately, it is natural for lawn grass to be dormant in the heat of summer so there is little need to worry about that.
For more information about these and other landscape gardening topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.