Cotinis nitida Linnaeus Coleoptera Scarabaeidae

Natural History

Distribution. Green June beetle is found principally in the southeastern states. It occurs north to southern Connecticut and southern Illinois, and west to Kansas and Texas. This insect is native to North America.

Host Plants. This insect is well known for the feeding habits of the adult stage because the injury of this stage is very visible. The adults feed commonly on ripening fruits such as apricot, apple, blackberry, fig, grape, nectarine, pear, plum, prune, quince, raspberry, and strawberry, which explains an alternative common name of this species—"fig eater." The adults will occasionally feed on vegetables, particularly the ears of corn, and the fruits and vines of melon and tomato. They also are attracted to, and feed upon, the sap, pollen, nectar, and flowers of trees. The larval stage has a broader range of hosts, however, and undoubtedly does more damage, but it is a less visible form of injury. Larvae feed below-ground on the roots of such vegetables as bean, beet, cabbage, carrot, celery, collards, corn, eggplant, endive, lettuce, parsley, parsnip, pea, potato, turnip, and likely others. Larvae also feed on the roots of lawn grasses; such field crops as alfalfa, oat, sorghum, and tobacco; and such ornamentals as dahlia, geranium, hyacinth, rose, and violet. Larvae apparently are capable of developing on decaying organic matter, and soils which are rich in humus or manure are suitable for larval development and are attractive to ovipositing females.

Natural Enemies. Several natural enemies of this beetle are known. Vertebrate predators such as skunks, chipmunks, opossums, and moles, as well as many bird species, have been reported to feed upon green June beetle larvae. Also, Sarcophaga spp. (Diptera: Sarcophagidae) have been reared from pupae and adults of the beetle. The digger wasp Discolia dubia Say (Hymenoptera: Scoliidae) is particularly attracted to the tunnels of the beetle larvae, where it paralyzes and parasitizes the larvae. The diseases have been poorly studied, but bacterial and fungal diseases have been observed, particularly the fungus Metarhizium anisopliae.

Life Cycle and Description. There is a single generation per year. Larvae are present for about 10 months, from August through the winter and spring, with larval development completed in the spring and pupation occurring during May or June. In Virginia, adults are present in June-August, with egg deposition occurring during July-August. In Georgia, Beckham and Dupree (1952) and Morrill (1975) reported high levels of adult emergence anywhere from late June through August, depending on the year.

  1. The adults apparently are attracted to sandy soil containing manure or decomposing vegetation for oviposition. The eggs are deposited in soil cavities dug by females. Clusters of 10-25 eggs are deposited at a depth of about 7-8 cm in a single cavity at the end of a tunnel, though the individual eggs are often separated by soil packed around the eggs by the females. The eggs are about 1.5 mm in diameter when first deposited, but within a day of oviposition swell to a diameter of about 3 mm as they absorb water. The egg is nearly spherical in shape and gray or dull white. Duration of the eggs stage is about 10-15 days. Females normally deposit 60-75 eggs, but sometimes up to 100 eggs, over a period of about a month. Domek and Johnson (1991) reported an oviposition rate of 2.2 eggs per day for apple-fed adults, mean longevity of 23 days, and an average fecundity of 50.8 eggs per female.
  2. There are three instars. The young larva, or grub, at hatching measures about 6 mm long, and is creamy white. The yellowish head soon turns brown. As the larva matures, the body color remains mostly grayish white or yellowish white, but the tip of the abdomen acquires a bluish or greenish color. The legs are relatively short and yellowish in color. The body bears many short, thick bristles of yellowish color. The larva bears ridges on its dorsal surface, and uses these to move along the surface of the soil. The larva measures about 16 mm in the second instar and about

28 mm in the third. Head capsule widths are about 1.2, 2.2, and 4.1 mm in instars 1-3, respectively. Duration of the first two instars is about 15 and 25 days, respectively. The third instar is the overwintering form, thus requiring about 9-10 months for maturity. Larvae normally burrow at depths of about 15-30 cm, but move deeper during cold weather. They maintain contact with the surface, often pushing soil to the surface during the night, creating small mounds of soil ("push-ups") not unlike large ant hills. They also have the unusual habit of crawling about the soil surface at night, normally crawling on their back. Larvae of all instars can be found crawling on their back above-ground during the evening hours. Young (1995) studied seasonal movement of larvae in Mississippi and reported first instars principally in August, second in September, and third in October. During the spring and early summer larvae are at their maximum size and activity level, and cause the greatest amount of damage.

  1. For pupation, the larva prepares a substantial cell of soil particles fastened together with fluid excreted by the larva. The cell is oval, measures about 16 mm long and 12 mm wide, and is found at a depth of about 20 cm. The larva transforms to the pupal stage within the cell, and resembles the adult in form except that the elytra and hind wings are wrapped ventrally. Also, the pupa is yellowish in color, acquiring a darker shade just before emerging as an adult. The pupa measures about 25 mm long and 12 mm wide. Duration of the pupal stage is about 20-30 days.
  2. The adult is distinctive in form and color. It is fairly large, measuring about 20-30 mm long and 12-15 mm wide. The body width is notably greatest

Green June beetle larva.

Green June beetle larva.

Terminal abdominal segment (ventral view) of green June beetle larva.

at the base of the elytra. Dorsally, the color of the beetle is velvety green or brown, with a light band of brown or orangish yellow at the margins of the elytra. The orange color may extend to other portions of the elytra. The lower surface is metallic yellow or green. Adults are active from about dawn until noon, and males produce a buzzing sound while flying low to the ground in search of mates. Males use pheromones to locate females, and often several males can be observed competing for the opportunity to copulate with a single female. Mating is relatively brief, lasting only a few minutes, and then the females descend into the soil. The female's burrowing results in production of soil mounds similar to that produced by larvae; thus, adults can be troublesome on golf courses. (See color figure 120.)

Good summaries of green June beetle biology were given by Davis and Luginbill (1921) and Chittenden and Fink (1922). There is evidence of a female sex pheromone and an aggregation pheromone (Domek and Johnson, 1987; 1988), but they have not been characterized. For the aggregation pheromone, a beetle food source and yeasts are implicated in pheromone production (Domek and Johnson, 1990).

Damage

The adults cause injury by feeding on the leaves and fruit of various fruit and vegetable crops. Larval feeding is more important, but less apparent, because it occurs below-ground. Not only do larvae feed on the roots and succulent stems of various plants, but their tunneling habits can be quite destructive to root systems, resulting in uprooting of young plants. On lawns, and particularly on golf courses, the soil pushed upward as larvae tunnel to the surface creates small disfiguring mounds.

Management

Sampling. Organic matter, incuding rotting or composted animal manure and vegetation, is highly

Cotinis Nitida
Adult green June beetle.

attractive to ovipositing females. Fields containing high levels of such soil amendments should be carefully monitored for larvae. Soil sampling normally is required to get good estimates of grub abundance, but the mounds resulting from the adult and larval habit of pushing soil to the surface can be indicative of insect densities. Also, pitfall traps can be used to capture larvae as they move over the soil surface at night. Larvae can also be brought to the surface by flooding or heavy application of irrigation water.

The adults are attracted to many volatiles. Fermenting sugar and molasses, malt extract, and isopropyl alcohol can be used as a lure for beetles (Beckham and Dupree, 1952; Landolt, 1990).

Insecticides. Insecticides can be applied to the soil to prevent injury by grubs. Application to the furrow or over the top of the row at planting is preferred for annual crops, whereas in turf broadcast application is required. Adults also can be controlled by application of insecticides, though susceptibility varies considerably among products (Thurston et al., 1956).

Cultural Practices. Previously larvae were routinely captured with pitfall traps positioned at the soil surface. Such traps take advantage of the night-time movement of grubs. The simplest type of trap is a container such as a coffee can that is buried in the soil with the top level to the surface of the ground. Because larvae tend to accumulate in furrows, traps positioned in furrows tend to capture more larvae. Troughs or artificial furrows can be constructed by attaching two boards lengthwise to form a "V" and sinking the trough into the soil. The relatively steep, slippery sides prevent larvae from escaping once they fall into the trough. Such practices have little use in commercial crop production but may find favor with home gardeners.

Plowing is often suggested as a remedy for grub infestation. The physical disruption associated with plowing, and the potential for predation of grubs by birds, are cited as benefits. However, in the case of green June beetle, the grubs tend to be located too deep in the soil during the normal spring or autumn plowing periods to be much affected by tillage. When grubs are near the surface, plants typically are in the field and also susceptible to damage by tillage.

Biological Control. Entomopathogenic nematodes (Nematoda: Heterorhabditidae and Steinerne-matidae) have been evaluated for control of green June beetle larvae (Townsend et al., 1994). The beetle larvae were reported to be somewhat resistant to infection because though about half of the larvae perished under optimal conditions of infection, the nematodes failed to reproduce in the cadavers.

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