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UNITED STATES DEPARTMENT OF AGRICULTURE 

 BUREAU OF ENTOMOLOGY 

 WASHINGTON, D. C. 



FCftEST ENTOMOLOGY BRIEF 8. April 3, 1916. 



Revised September 24, 1919. 



SCALE INSECTS ON SHADE TREES and SHRUBS 

 and REMEDIES FOR THEM. 



Appearance and Habits.- Scale insects are so called because of the scale that covers or 

 constitutes the baclc of roost of them. This scale may he horny, leathery, waxy, 

 cottony, or mealy and just as various in size, shape, and color. There are many 

 species of scale insects and, according to the consistency of the scale, they 

 are roughly divided into armored (horny) scales, soft (leathery) scales, cottony 

 scales, mealybugs, etc. Except for a few days after hatching, when they are 

 nak;?d, these insects are nearly always covered by the scale characteristic of 

 the species to which they belong. The nurabor of generations annually, date of 

 hatching, and other life history habits vary with the species, season, and lo- 

 cation. They are all plant feeders, some confining themselves to a single 

 species of plant while others occur on a great variety of plants. They occur on 

 roots, main stems, branches, and twigs; some of them occur also on the leaves and 

 fruit in summer. They feed on sap which, by means of their slender, flexible, 

 needle-like beaks, they suck up from within the plant tissues. They are, there- 

 fore, classified as sucking insects. Some of them produce more or less honeydew 

 which attracts ants, bees, v/asps, etc., which eat it but do not harm the plants. 

 Old honeydew frequently gives the affected plants a sooty appearance. 



Natural control.- Like other insects, most scale insects are usually kept in check by a 



variety of natural agencies, especially parasitic and predacious insects. Under 

 such conditions they do no permanent serious harm and require no remedial treat- 

 ment. Quite often, hov/ever, some species become so numerous as to be very in- 

 jurious and make early treatment imperative if the value or life of the affected 

 plant is to be saved. 



Remedies.- (See accompanying brief on Scale Insect Remedies.) 



Being sucking insects, scale insects can not be killed by means of stomach poisons. 

 They are controlled mostly by being covered at the proper season with a 

 liquid substance which, without injuring the plant, kills the insect by 

 either clogging its breathing pores or penetrating to its vitals, or both. 

 The aim must be, therefore, to cover every individual insect that needs to 

 be killed. The covering is effected by means of a spraying device which may 

 be a tin atomizer, a bucket, knapsack, or barrel sprayer, or a power spraying 

 machine, depending on the extent of spraying contemplated. 



Winter spraying, done when the buds are dormant, is preferable for scale insects 

 because (1) there is then no delicate foliage to injure and none to conceal 

 insects or to use up spray; (2) dead and superfluous portions of the plant 

 may and should then be removed, still further reducing the area to be sprayed 

 and exposing the insects; (3) plants are then dormant and can withstand strong- 

 er sprays without injury. 



Summer spraying, when imperative, is most effectively done when the young are at 

 the height of hatching, i.e., crawling about in numbers. 



A. D. HOPKINS, 



Forest Entomologist, 



