ROSE CHAFER, Macrodactylus subspinosus (Fabricius)
Description and Life Cycle
Rose chafer adults attack grapes at bloom as they emerge from the soil. Not only due they destroy the fruit at blossom, in addition, they frequently skeletonize the leaves, leaving only the large veins intact. This insect is especially abundant in areas of light, sandy soil where beetles may appear suddenly as grapes begin to bloom.
The ungainly beetles have a straw-colored body, reddish-brown head and thorax with black undersurface. The adult rose chafer is about 0.5 inches in length with long, spiny, reddish-brown legs that gradually become darker near the tip. As they age, hairs are worn off the head and thorax with normal activity revealing the black color below. Thus, they become mottled in color as they mate and move around in the flower clusters making it possible to distinguish newly emerged adults from older specimens. Females frequently loose more hairs, particularly on the thorax, in the mating process. Eggs of the rose chafer are oval, white, shiny in appearance, and about 0.05 inches long and 0.03 inches in width. Larvae are C-shaped white grubs about 0.8 inches long and 0.12 inches wide when fully grown. Mature larvae have three distinct pairs of legs, a brown head capsule, and a dark rectal sac visible through the integument. Larvae are found in sandy soil feeding on grass roots and can be identified by a distinctive rastral pattern. The pupae are light yellowish-brown in color and haveprominent legs. They measure about 0.63 inches in length.
Adult rose chafers become active in northeastern North America from late May to early June. The adults appear suddenly. It seems as though the entire population reaches maturity practically at the same time, and multitudes of beetles suddenly make their appearance. Beetles feed and mate soon after emerging from the soil. It is common to see mating pairs in the newly formed grape clusters. Females deposit eggs singly a few centimeters below the soil surface. Mating and egg laying occur continuously for about two weeks with each female depositing 24 to 36 eggs. The average lifespan of the adult is about three weeks.
Approximately two weeks after being deposited, eggs hatch into tiny, white, C-shaped grubs. The larvae feed on the roots of grasses, weeds, grains, and other plants throughout the summer, becoming fully developed by autumn. However, it is not easy to collect the larvae of rose chafer. They have been found occasionally on the roots of orchardgrass but never in proportion to the numbers of adults found in adjacent grapes. Larvae move downward in the soil as soil temperatures decline and form an earthen cell in which they overwinter. In the spring, larvae return to the soil surface, feed for a short time, and pupate in May. After two weeks in the pupal stage the adults emerge and crawl to the soil surface to begin their cycle again. There is but one generation per year.
Despite its common name, the rose chafer attacks the flowers, buds, foliage, and fruit of numerous plants including grape, rose, strawberry, peach, cherry, apple, raspberry, blackberry, clover, hollyhock, corn, bean, beet, pepper, cabbage, peony, and many more plants, trees, and shrubs. Adults emerge about the time of grape bloom and often cause extensive damage to foliage. Blossom buds are often completely destroyed, resulting in little or no grape production. Feeding activity on various plants may continue for four to six weeks. Damage can be especially heavy in sandy areas, the preferred habitat for egg-laying. A toxin present in the beetles may kill poultry.
Adult chafers begin emerging in late May and early June at the time of grape bloom. A spray application is recommended if more than 2 beetles per vine are present. If only a few beetles are present , they may be handpicked from the vine and destroyed. The pupal stage is extremely sensitive to disturbance therefore, cultivating between rows may be effective in destroying a good number of chafers, however it is our experience that growers with sufficient numbers of beetles to inflict economic damage will not be able to control this pest by this method of cultural control. An alternative method to chemical control has been developed by the department of Entomology at Ohio State University for this pest. This method utilizes a very powerful feeding attractant and a Japanese beetle trap. Intensive trapping over a 4 year period reduced the population to below the threshold level of two beetles per vine. An application of insecticide may required in combination with the trapping effort if the population is extremely high. It is our experience that it takes a couple years of intensive trapping to reduce the population within a heavily infested vineyard to the point that chemicals are no longer needed to control this pest.
Scouting for this pest within your vineyard should begin in late May and continue through late June. Newly emerged adults may be found feeding upon young grape buds and foliage. If numbers reach 2 beetles per vine control methods should be utilized. Monitoring may also be conducted by utilizing the attractant developed for rose chafer. Traps should be placed around the perimeter and dissecting the vineyard. For monitoring purposes these traps may be spaced every 100 ft. and should be checked daily for newly emerged chafers. If beetles are encountered, control methods should be considered if beetles average 2 or more per vine.
When only a few beetles are present one may handpick them from the plant and destroy them. Where populations are large and pose a threat to the grape crop, massive trapping may be a safe alternative to applying insecticide. Results utilizing this new powerful attractant have been very positive. The desired effect of mass trapping, which is to bring the beetle population to below threshold level, is usually achieved after a couple years of trapping. Chemical control methods should be utilized when beetle pressure exceeds an average of two beetles per vine. To determine the number of beetles per vine one should randomly survey 25 vines at all four corners of the vineyard and 25 in the center of the vineyard. This will give you the total number of beetles present on 125 vines surveyed. Divide the number of vines (125) by the number of beetles present to obtain the average number of beetles per 125 vines. If this average is above 2 beetles per vine, then treatment is recommended. It should be noted that, with this survey method, one can determine if the chafer infestation is present throughout the vineyard or just located in a specific area. If the area is localized, spot treatment of the infestation may be all that's required. Treatment with an insecticide should be after bloom when the first newly emerged beetles are detected in adequate numbers to pose concern. A second application may be required if pressure is severe and rainfall is frequent. Protection of the young grape cluster is critical and should be maintained throughout June.
Current pesticide recommendations may be found Here