ARBORICULTURE 



ARBORICULTURE 



367 



341. Woolly aphis on alnus, 



ity of the tree. In addition, the leaves may be dis- 

 figured by a sticky substance, known as honey-dew, 

 secreted by the insects. In the fall, both females and 

 winged males are produced and the female laj's a single 

 winter egg. On account of their method of reproduc- 

 tion, plant-lice multiply very rapidly, especially in 

 damp seasons. Some species have a more complicated 

 life-cycle, producing winged individuals in the summer 

 which migrate to another food-plant, later to return 

 in the fall to the original one. 



A few plant-lice living in colonies produce galls, 

 curled leaves, or otiier malformations on the leaves or 

 twigs of infested trees. 



Scale insects exhibit a greater variety in their sea- 

 sonal history; some pass through a single generation 

 each year, while others multiply more rajjidly, passing 

 through a number of generations annually. The win- 

 ter is .sometimes passed in the egg state, but more 

 commonly as a partly grown insect. 



One of the commonest and most destructive scales is 

 the oyster-shell scale, Lepidosaphes ulmi. This occurs 

 on the thin bark of a great variety of trees, appearing 

 as a very small, elongate, flattened body, pointed at one 

 end and rounded at the other, with the upper surface 

 more or less distinctly ridged in a transverse direction. 



There is a single 

 generat ion an- 

 nually, the fe- 

 males maturing 

 in late summer 

 and depositing 

 a mass of eggs 

 which remains 

 beneath the 

 scale through 

 thewinter,hatch- 

 ing in the spring and producing full-grown insects by 

 midsummer. Sometimes this species is so abundant 

 that the smaller branches appear as if covered by a 

 gray incrustation. 



The San Jose scale, Aspidiotus perniciosus, is another 

 important scale, which has been introduced into many 

 parts of the United States. It is very destructive, 

 primarily to certain orchard trees, but injures many 

 thin-barked shade trees as well. The scale is very small, 

 round in the female and oval in the male, with a minute 

 nipple-shaped projection near its center. The females 

 do not lay their eggs till the yoimg insects are ready to 

 hatch, so that they practically produce living young. 

 These develop rapidly, five or six broods maturing each 

 season, of which the last hibernates in the half-grown 

 condition. In mass, the scales form a gray, granular 

 crust, covering the branches and twigs. 



In some parts of the country, maples grown for shade 

 trees suffer great injury by the cottony maple scale, 

 Puliiinarin innumerabilis. This scale is most conspicu- 

 ous on the twigs in early summer, at which time the 

 females are depositing their eggs. It then bears a tuft 

 of fluffy waxen substance resembling a bit of white 

 cotton. The young scales appear soon after, when they 

 migrate to the leaves and feed till early fall before 

 returning to the twigs, where they finally pass the 

 winter in a half-grown condition. 



Practically all sorts of trees suffer at times from scale 

 insects, of which there are many kinds. The common 

 forms are divisible into two groups, the soft scales and 

 armored scales. The former arc soft and convex like 

 the cottony maple scale, in which the "scale" is the back 

 of the insect itself; the latter are usually smaller, like 

 the San Jos6 scale, in which the "scale" is a separate 

 waxen cover secreted by the in,sect. 



c. Bark-beelles. 



These insects are small black or brown beetles that 

 hvc in the larval stages beneath the bark, feeding on 

 the inner bark and cambium, and all have very similar 



342. Flat-headed borer. 

 (Natural size.) 



habits. The parent beetle enters the bark through a 

 small hole about the size of a pencil-lead, and excavates 

 a single primary or egg-gallery through the cambium, 

 usually grooving the sapwood. This tunnel varies from 

 one to several inches in 

 length, and along its 

 sides the female cuts out 

 little pockets, in each of 

 which an egg is laid. On 

 hatching from the eggs, 

 the larvaj excavate in- 

 dividual mines usually more or less perpendicular to 

 the egg-gallery. When full grown, the white leglesa 

 grub-like larviB pupate in cells excavated in the bark, 

 from which the beetles emerge by chewing out a circu- 

 lar tunnel to the surface. Trees from which beetles 

 have emerged appear as though the bark had received a 

 charge of buck-shot, from the presence of the small cir- 

 cular emergence holes. Some forms, like the genus Den- 

 roctonus, attack fine healthy coniferous trees and kill 

 much valuable timber, but shade trees are more com- 

 monly attacked by the species that live in the bark of 

 deciduous trees, more particularly those that are in 

 a sickly condition. 



A common form is the hickory bark-beetle, Eccop- 

 togaster quadrispinosa, that attacks hickories. The 

 beetles appear in June and July, to excavate the pri- 

 mary galleries which extend vertically for an inch or two. 

 Fort.y or fifty eggs are placed in notches on the sides and 

 the larvEe bore out at right angles, thus girdhng the 

 cambium and weakening or killing the branch. This 

 species undergoes only one generation annually, although 

 some others pass through two or more each season. 

 There are many other kinds, all scarring the bark or 

 surface of the wood in a similar way. 



D. Wood-borers. 



The larvEe of many beetles and moths, and of a few 

 wasp-like insects, injure trees by excavating their food- 

 burrows through the solid wood. 



Birches, grown for shade or ornamental trees, often 

 suffer great injury from the presence of a flat-headed 

 borer, the bronze birch -borer, Agrilus anxius. The 

 small elongate bronze-green beetles appear in May or 

 June and deposit their eggs on the branches, at first 

 near the crown of the tree. The larviE penetrate the 

 bark, beneath which they cut irregular flattened gal- 

 leries till grown, when they cut out cells in the wood in 

 which to pass the winter before emerging in the spring. 

 The upper parts of the tree suffer first and begin to die, 

 and the following year the larvae appear nearer to the 

 ground. Chestnut is attacked by Agrilus bilineaius, the 

 two-lined chestnut-borer. 



Most other kinds of trees suffer similar injury from 

 related beetles, many of which multiply also in dead 

 trees and stumps. 



Another flat-headed borer, the larger flat-headed 

 pine-borer, Chalcophora virginiensis (Figs. 342, 343), 

 extends its flattened burrows deep into the wood of the 

 tree, a method of feeding exhibited by many borers of 

 this group attacking deciduous trees also. The larvae 

 grow to a length of 2 inches before 

 cutting out their transformation cells 

 in the bark. 



Round-headed borers are similar in 

 habits, but belong to another family 

 of beetles in which the larva; are less 

 distinctly flattened near the head 

 and excavate more nearly cyUndrical 

 burrows. 



One of our commonest species is the 

 locust-borer, Cyllene robinis', which 

 attacks yellow lot^ust trees. The 

 elongate medium-sized black beet- 343. Chalcophora 

 les, with brilliant yellow markings, ^Sf'teaded Wer"' 

 appear in the early fall to deposit (Naiural size.) 



