Insects hijarious to the Apple. 



169 



antenna?. These grey, larval scale insects crawl from beneath 

 the dried scale, and wander about freely over the tree. Sooner 

 or later they fix upon some definite spot, plunge their long beaks 

 into the plant, and then commences a most remarkable series of 

 changes. 



Soon after hatching the larva becomes covered with a greyish- 

 white substance. At tliis time, the young scale insects may readily 

 be seen on the trees as small whitish specks. If the larva is destined 

 to become a female it never moves again. At first the larva is quite 

 unprotected, but by degrees a waxy excretion exudes from its skin, 

 and the rudiments of a scale form over it. Tlien it casts its skin 

 and this cast skin also fuses with the waxy covering, and forms that 

 smaller area mentioned before, seen on the front of an old scale. 

 The cast skins entering into the forma- 

 tion of the coccid scale are the so-called 

 exuvite. When the little active larva 

 moults it loses its legs, its feelers, its 

 bristles, and so becomes converted 

 into a footless, almost structureless 

 body, the adult female. We see no 

 pupal stage as noticed in tlie aphis. 



Let us now see what happens if 

 the larva is to become a male. It 

 first settles down and, just as in the 

 female, it forms a protecting covering 

 composed of excretions and cast skins, 

 but of very different form from that of 

 the female. Xow this larva, instead 

 of degenerating as did the female, 

 casts its skin and enters a kind of 

 pupal stage, called the propupa, in 

 which we find limbs and rudiments of wings forming. When 

 matured, this pupa casts its skin, and from beneath the scale 

 there issues forth a winged insect. The male scale insect has tu-o 

 wings, very different from the four-winged aphis, the single pair 

 of wings having but one ibrked vein to support them. The end 

 of the body is prolonged into a long tube. This tube is inserted by 

 the male under the female scale, and so the female is fertilised. The 

 male then dies. The male mussel scale may now and then be found ; 

 but not a hundredth part of the females which lay eggs are ever 

 fertilised by a male. They, like the aphis, can produce asexually, 

 that is, without the agency of a male. 



Scale, fti and a ; normal bark 

 glands, h, t ; u, c, cankered scars ; n- ova. 



