Fig. 40. Eggs of grape-vine flea-beetle.
In the warm days of May and June when the buds of grapes are swelling, a shining steel-blue beetle may often be found in the vineyards of eastern America feeding on the tender buds of the grape. From its color the insect is often called the steely-beetle, and from its activity and habit of jumping it is known as the flea-beetle (Haltica chalybea). The vine is seldom seriously injured by this pest but many buds are destroyed, causing the loss of the fruit that should have developed from the buds. It is true that new buds often develop after the injury, but these, as a rule, produce only foliage.
The life history of the flea-beetle is such that the pest is not hard to control, the chief steps in its development being as follows: The beetles deposit small orange-colored eggs, cylindrical in form, illustrated in [Fig. 40], about the buds and in crevices of the bark of the canes in May or June. Most of these eggs are hatched by the middle of June. The larvæ feed upon the foliage until about July first and then crawl to the ground in which they form cells and pupate. The latter part of July the adults emerge and seek wild vines upon which they feed, entering hibernation rather early in the fall. The beetles hibernate under leaves, in rubbish and in the shelter of the bark of trees and vines, but emerge in the warm days the following spring to seek vineyards.
Two methods of control have been developed to keep this pest under. The vines should be sprayed with three pounds of arsenate of lead in fifty gallons of water when the larvæ are feeding on the foliage; or the beetles when feeding may be knocked into a pan containing a shallow layer of kerosene. The former is the cheaper and more effective method provided the grape-grower has the foresight to discover the larvæ, since the larvæ of this summer produce the beetles that will destroy the buds next spring. When the adults migrate from wild vines, or the larvæ were not destroyed in the vineyard, collecting the adults is the only practical method. The destruction of wild vines near a vineyard helps to give immunity from this pest.
The rose-chafer.
The rose-chafer (Macrodactylus subspinosus), a long-legged beetle of a yellowish-brown color, about a third of an inch in length, often appears in vineyards in vast swarms toward the middle of June in northern states and about two weeks earlier in southern states east of the Rocky Mountains. Often they overrun gardens, orchards, vineyards and nurseries, and usually, after having done a vast amount of damage in the month of their devastating presence, the beetles disappear as suddenly as they came. Vineyards on or near sandy soils are most often infested, the larvæ of the beetle seeming to live in considerable numbers only in these light soils. The chief damage to the grape is done to the blossom; in fact the insects, after feeding on the blossoms during the blossoming period, usually migrate to blossoms of any one of several shrubs. The larvæ feed on the roots of grasses, having particular liking for the roots of foxtail, timothy and blue-grass.
Some knowledge of the life history of these beetles is essential to effective control. The beetles emerge as adults in June and after feeding a short time begin to mate, although egg-laying does not take place until the insects have been out for a fortnight or more. The females burrow into the soil and deposit their eggs, seldom more than twenty-five in number, which begin to hatch in about ten days. The young larvæ feed during the remainder of the summer on roots of grasses. They are seldom found deeper than six inches while feeding, but as cold weather approaches they burrow deeper to avoid sudden changes of temperature. The following spring they again come near the surface to feed. The grubs form cells from which the pupæ emerge, as we have seen, about the middle of June, timing their appearance very closely to the blossoming of Concord grapes.
The methods of control are three, namely: destruction of the larvæ; cultivation to kill the pupæ; and spraying to kill the beetles. Since the larvæ feed on the roots of grasses in sandy soils, it is easy to locate the feeding ground of the pest and plant it to cultivated crops which destroy the grasses and therefore the larvæ. The second method of destruction is similar, consisting of cultivation to kill the pupæ. This is accomplished by thorough cultivation during the pupating stage to break the cells and crush the pupæ, thus preventing the emergence of the beetles. The third method, however, is the most effective and consists of spraying the vineyard with a sweetened arsenical spray. The spraying should be done as soon as the beetles appear, using arsenate of lead six pounds, molasses one gallon and water one hundred gallons. It is often necessary to make a second application a week later. If rain occurs within thirty-six hours after spraying, the application should be repeated as soon as the weather clears.