404 ECONOMIC INSECTS 



with which the insects multiply. If a few are left in the orchard 

 in the spring they may multiply and spread so rapidly as to kill 

 some trees and infest the whole block of trees by fall. They are 

 very small and may easily escape detection. The young are carried 

 from tree to tree by other insects and on the feet of birds. 



Several spray materials are successfully used in controlling 

 the scale. The most successful are: (1) Soluble oils, or miscible 

 oils, and (2) lime-sulfur preparations. Lime-sulfur has the great 

 advantage of being a good fungicide, as well as a good insecticide, 

 for this class of insects. It is clained for the soluble oils that they 

 will last longer and will destroy insects that may be brought to 

 the tree after it is sprayed. 



Both materials are used when the trees are in the dormant 

 stage. The very dilute self-boiled lime-sulfur is also used on trees 

 when the foliage is well developed. 



Canker worms, sometimes called measuring worms, attack 

 apple trees and sometimes pears and others, defoliating them. 

 These larvae are very difficult to poison. Strong solutions of arse- 

 nate of lead are most successful. Spraying should be done while 

 the larvae are very small when their work is first seen. 



Another method of control is learned from the knowledge of 

 their life history. The female moths are wingless and must crawl 

 up the trunk of the trees to lay their eggs on the leaves, where the 

 larvae may feed. Bands may be placed around the trees to pre- 

 vent the ascent of the female moths or the larvae. The band may 

 be made of a soft tar-like preparation, or may consist of wool or 

 cotton tied on with cord. There are commercial preparations 

 used for this purpose, and sticky fly paper is sometimes used. 



Two Apple Tree Borers. The more common apple tree borer 

 is called the flat-headed borer. The eggs are laid on the bark of 

 tree trunks and the larvae dig and feed chiefly in the sap wood. 

 They live from one to three years before emerging as adults. They 

 are then beautiful bronze or black beetles, which live for only a 

 short period. 



The work of the borers should be observed closely and the larvae 

 may be killed by use of a wire or a knife. 



The round-headed apple tree borer is usually less common 

 than the other, but its work extends deeper after the first year and 

 it is more difficult to remove from the deep channels. The larvae live 

 for about three years, after a short pupal stage, appearing in early 

 summer as brown-and-white striped beetles. (Figs. 276 and 277). 



