Cotinus nitida (Linnaeus)
Home lawns in select areas of Pennsylvania often are subject to severe and extensive injury from green June beetle grubs (Fig. 1). Green June beetle is also called the fig-eater because of its fondness of ripe figs and other thin-skinned fruit. Researchers have stated that this insect is a native pest with a wide distribution from Connecticut and southeastern New York to Florida and westward into Texas, Oklahoma, and Kansas. Over the past 30 years, green June beetle has received minimal attention, except when the big adults were active fliers in July, especially since their buzzing sound during flight resembles that of bumble bees. However, this insect is now recognized as a turfgrass pest, especially in southeastern and southwestern Pennsylvania.
Figure 1. Larval stage of Green June Beetle
Adult beetles are ¾ to 1 inch long. The adult's upper body is velvety green to dull brown with lengthwise stripes of green with yellow-orange margins on the hardened front wing. The underside of the body is shiny metallic green or gold. Adults also have a distinct, small, flat horn on the head (Fig. 2). Green June beetle grubs are 3/8 (first instar) to 1½ inches long with a white stubby body and short legs. The grubs have an unusual habit of crawling on their backs rather than relying on their small legs, which are extended upward as they move across surfaces. Ridges located on the upper surface of the grub's body are covered with short, stiff hairs that assist them in moving on the surface of the grass.
Figure 2. Adult Green June Beetle - Image courtesy of Susan Ellis, www.insectimages.org
General Life History
This insect completes one generation annually. Green June beetles overwinter as mature grubs and resume feeding in the spring. Pupation occurs from May through June. Prior to pupation, the third-instar larva forms a protective case composed of soil particles bound together by a sticky secretion. Adult development usually requires 16 to 18 days. Then adults emerge from the soil to mate. Females fly over the turf's surface early in the morning, while males fly from mid- to late morning. Females produce a substance that attracts the males to them prior to mating. After females mate, they dig into the turf to lay a cluster of 10 to 30 eggs in a compacted ball of soil about the size of a walnut. Females prefer moist organic soil. The eggs are nearly round, about 1/16 inch in diameter, absorb soil moisture, and hatch in 10 to 15 days. The grubs are nocturnal feeders and consume decaying organic matter. Larvae molt three times until they reach the third instar. As cool fall temperatures arrive, the nearly mature, 1½-inch third-instar grubs dig deeper in the soil to overwinter.
Green June beetle grubs, especially third instars, burrow to the surface at night to feed and may at times graze on turf. Soil accumulating at the surface resembles earthworm castings. Early instar grubs frequently can be found tunneling in the top 4 inches of soil. They will loosen the soil and eat or thin out the thatch. Grubs seldom consume enough turf roots to cause significant damage. However, their disruptive burrowing and mound-building activities can disfigure turf. The latter mounds frequently are 2 to 3 inches in diameter; plus, grubs leave distinct open, vertical soil burrows averaging 6 to 12 inches in depth. The diameter of the burrow is about the size of your thumb. University of Maryland researchers have reported that drought-stressed grass that is maintained at a very short height succumbs easily to this type of damage. Likewise, mounds of soil can dull reel-type mowers. It is also interesting to note that after a rain, grubs may end up on sidewalks, in the garage, or in ground-level swimming pools. Adult beetles injure various types of ripening fruit.
Be sure that you have green June beetle grubs present before selecting a registered control measure. It is important to recognize that this grub species is not the only animal that makes mounds on grass. Earthworms also make mounds, the particles of which are distinct pellets. You can sample for green June beetle grubs by removing a few soil samples with a shovel. Turf samples should be about 1 square foot and about 2 to 4 inches deep. You will need to sift through the soil to determine if grubs are present. Also, maintain a record of where green June beetle adults are flying throughout the summer months.
Nonchemical - Cultural
Maintain a health lawn that can enhance turf vigor, which will assist in masking grub damage and encourage recovery. Some homeowners may want to consider overseeding thinned-out damaged areas in the fall to reduce weed encroachment the following spring.
Nonchemical Curative - Biological
Insect-parasitic nematodes are available to curatively suppress white grubs. Two major species are available for suppressing grubs: Steinernema spp. and Heterorhabditis spp. Insect-parasitic nematodes do not have a long shelf life. Likewise, be sure to follow all label directions regarding irrigating in this organism immediately following their application. If you rely on this nonchemical control method, then you need to remember that these nematodes are living, breathing organisms and should be handled with special care. Prior to applying this type of curative control measure, be sure to check the expiration data on each package of insect-parasitic nematodes. It is important to select the proper nematode species when trying to control a particular pest. Thus, read the label carefully prior to making your selection. Follow all specific label directions.
Green June beetle grubs are parasitized by a type of digger wasp, Scolia dubia (Say). These wasps are usually most abundant during August. Adult female wasps dig through the soil in search of grubs. Once located, the wasp paralyzes the grub and lays an egg on the grub. The egg hatches into an immature wasp larva, which uses the grub as a source of food to complete development. Adult wasps usually feed on nectar and pollen of flowers. This beneficial insect often is referred to as the blue-winged wasp. The adult is ½ inch long with black antennae, shiny black head, and two yellow spots (one on each side) midway along the last major body segment (abdomen). The tip of the adult wasp's abdomen is brownish, while the wings are dark blue. It is interesting to note that adult wasps are often noticed flying only a few inches above turfgrass infested with grubs. In some cases, these wasps have been observed in large numbers and are conspicuous as they fly their mating dances.
Chemical - Curative Home Lawn Green June Beetle Strategy
The most common method of controlling this insect is to rely on a late-summer through early fall curative application. Unfortunately, this treatment usually is completed after green June beetle grub damage is noticeable on home lawns, including the presence of tunnels and small mounds of soil located on the surface of the grass. These grubs are relatively easy to control at this time with an application of a contact insecticide; however, it is important to recognize that a late-summer/early fall application can result in dead grubs on the turf surface. Ideally, curative applications should be made late in the day since grubs move to the surface during the evening. These insects die at night on the surface rather than in soil burrows. Thus, you may end up with a large number of dead, smelly grubs on the surface of your grass. In some cases, you may need to remove the decaying dead grubs. Also, keep a history of the site infested with green June beetle grubs for a future reference guide. Thus, read the label carefully prior to making your selection.
Chemical - Preventive Home Lawn Green June Beetle Strategy
Insecticide formulations labeled for preventive grub control usually state that the product should be applied before grubs hatch, when they are newly hatched, or when they are young and actively feeding. Prior to purchasing a product, be sure to read the label regarding the optimum time to treat for grubs.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Paul Heller, Professor