THE WOOLLY APPLE APHID, a pest widely distributed throughout all apple-growing areas in the United States, has been held in check by the parasite Aphelinus mall. This aphid is the insect that lives in the little cottonlike masses that are often seen around pruning wounds and other scars on the trees and in the axils of leaves on new growth, particularly on water sprouts. It may also occur on the roots of the trees. A particularly important pest in the Pacific Northwest because of its connection with spread of the perennial canker disease, it is only in that area that it has increased to serious proportions following the use of DDT. Presumably because of the effect of DDT on the Aphelinus parasite, the woolly apple aphid is once again a pest to be reckoned with in that area.

Formerly controlled with nicotine sulfate when the parasite did not take care of it, it can now be checked by including materials such as benzene hexachloride, parathion, or TEPP in an early cover spray, or controlled later with either of the latter two materials. Benzene hexachloride may impart an off-flavor to the fruit if used after the early part of the season.

THE PLUM CURCULIO, an important fruit pest east of the Rocky Mountains, is most commonly associated with stone fruits, particularly peaches and plums. On apples it seldom caused serious injury when the regular spray program included lead arsenate to control the codling moth. Ordinary dosages of DDT do not control it effectively. Its jump in importance to apple growers dates from the time they changed their spray programs from lead arsenate to DDT. The best answer has been to include lead arsenate in the early-season part of the spray program, especially in the calyx and first-cover spray. For heavy infestations a special application between the calyx and first-cover spray is often desirable. Other materials show promise, but none seems to be superior to lead arsenate for use against plum curculio on apples.

APPLE GROWERS have known the San Jose scale for many years, but few were familiar with Forbes scale, which is like it in appearance and habits. Many growers in the Midwest now are concerned with both species. Long held under control by the use of dormant- and summer-oil emulsions, the scales are growing in importance as the use of oil in the regular spray program steadily declines.

Dormant-oil emulsions at ordinary strengths, usually 3 percent oil in the dilute spray, are highly effective against the San Jose scale but do not seem to be so effective against Forbes scale. It appears that former wide use of oil in summer cover sprays may have had more effect in scale control than was generally recognized.

Our experimental work has shown that dormant sprays may not be necessary to control either one of the scales if a material such as parathion is included in the regular spray schedule. The minimum effective dosage of parathion has not been determined, but one-fourth pound or more of 25 percent parathion per 100 gallons in six applications or one-half pound in three applications have given complete protection in tests in Indiana. A single summer application of one-half pound of 25 percent parathion per 100 gallons has given partial control of Forbes scale on apples.

Pacific mite.

I HAVE DISCUSSED only the pests that have created serious problems for years and in important producing areas following the use of DDT. Others, such as the yellow-necked caterpillar in West Virginia, Virginia, and Maryland and mealybugs elsewhere, have appeared for a season or two in limited sections, presumably (but not necessarily) because of a direct or indirect effect of the use of DDT. In general, effective treatments have been developed promptly or adjustments made in the spray program to control such outbreaks, and they have not proved too serious. Other ordinarily minor pests no doubt will appear in outbreak proportions from time to time and require temporary or continuing adjustments to take care of them. But the apple grower must be ever on the alert and his spray program must be a flexible one.

The reader should not conclude that increases in importance of previously minor pests following the use of DDT have been confined to apples or that DDT is the only one of the newer insecticides whose use has led to such developments. For example, the use of DDT has been associated with increases of mites on peaches, grapes, pecans, shade trees, and cotton; mealy-bugs on grapes; aphids on cotton; the red-banded leaf roller on peaches and grapes; and cottony-cushion scale on citrus. On the other hand, the use of materials such as methoxychlor has been followed by more mites on apples and peaches and aphids on cotton. The use of parathion has been followed by increases of the soft scale on citrus. But all in all DDT on apple trees has been more to blame than the others for outbreaks of pests that used to be of little importance. Despite the problems its use has created, DDT has been a great benefit to apple growers; advantages resulting from its use far outweigh its disadvantages.

HOWARD BAKER is assistant division leader of the division of fruit insect investigations, Bureau of Entomology and Plant Quarantine. He was graduated from the University of Massachusetts in 1923 and joined the Department immediately thereafter. After various field assignments having to do with the apple and pecan insects in the East, Middle West, and South, he was transferred to Washington in 1944.

Japanese beetle.