110 INSECTS AFFECTING VEGETATION 



which mat down and form the beginning of the scale covering. This 

 waxy secretion continues during the life of the insect, the covering 

 scale being enlarged as the insect increases in size. The females un- 

 dergo two molts, and the skins thrown off in these molts form a defin- 

 ite part of the scale, being cemented to it closely with the wax. 

 The female insect, after the second molt, soon reaches full size, and 

 when fertilized by the male begins to develop her numerous progeny. 



The preliminary stages of the male scale exactly correspond 

 with those of the female. After the first molt, however, the male as- 

 sumes a slightly different appearance, being more elongate than the 

 female at this stage. With the second molt the male diverges entirely 

 from the female ; the old skin is thrust out from beneath the covering 

 scale, and does not become a part of it, as w r ith the female, so that in 

 the case of the male insect the first-shed skin only is associated w.ith 

 the scale, which never becomes more than one-half the size of that of 

 the female. With this second molt the male insect transforms to a 

 preliminary pupal stage, in which the antennae, legs, and wings are 

 partially developed. A third molt occurs with the male insect, result- 

 ing in the final pupal stage, which exhibits more fully formed legs 

 and wings than the preceding stage and also the so-called terminal 

 style. A fourth and last molt of the male produces the perfect insect, 

 which escapes from beneath the covering scale and can fly about. 



The periods between the moltings vary with different species 

 and with w r eather conditions. Most of the species, however, reach full 

 growth in from four to six weeks in summer; development is slower 

 in winter. 



The female insect, having once thrust her beak into the tissues 

 of the plant as a larva and begun the secretion of a covering scale, 

 never moves from her position ; and, in fact, if she be removed by 

 force is never again able to penetrate the bark with her sucking beak, 

 and soon perishes. The opportunity for the local spread of these in- 

 sects is, therefore, limited absolutely to the larval stage, as in this 

 respect they differ from the Lecaniums and mealy bugs, whih have 

 the power to move about until nearly the end of their growing period. 



The number of eggs from a single female varies somewhat with 

 the species, but may be from 100 to 500, the number being less in un- 

 favorable seasons. The progeny from a single female in a year, if 

 they should all survive, would represent almost inconceivable num- 

 bers, running into the billions. It is not to be wondered at, there- 

 fore, that plants become thoroughly infested with these insects in a 

 very short time, especially in climates where the breeding is but little 

 checked by the winter season. 



The waxy covering makes it necessary to use rather strong 

 washes to penetrate the scale. The difficulty increases when the old 

 scale protects a mass of eggs, as is usually the case with the species of 

 Mytilaspis, represented by the long and purple scales; and it is not 

 always possible with the best washes to kill all the eggs of these 

 species, hence the necessity of spraying repeatedly to destroy the 

 young as they emerge. Remedial operations should be instituted as 



