212 



LEPIDOPTERA (MOTHS). 



fll-\ 



Diamond-hack Moth (Plutella waculipemm). 



In 1891 the east coast of Groat Britain was ravaged by 

 countless numbers of this moth, whose larvae feed on turnip, 

 cabbage, and most other cruciferous plants, devouring the 

 leaves down to the midrib. It was estimated that in a single 

 year this little pest, which is well known over most parts of 

 England, caused £20,000 worth of damage to root-crops alone. 

 Before that year and since it has done harm in many districts. 

 The moth, ^Yhich is a native, has long narrow wings, the fore 

 pair being reddish- or slaty-brown, with a pale yellowish-white 



border posteriorly ; the 

 hind -wings are grey, 

 with long fringes of 

 hair, a feature seen in 

 all Tineinse. When 

 the wings are folded 

 the pale edges of the 

 front ones come close 

 together, and form dia- 

 mond - shaped areas, 

 hence its popular 

 name. The moths (fig. 

 109) appear in June 

 and July, and lay 

 their eggs on the under-side of the leaves. The larvfe are at first 

 grey, then green in colour, about half an inch long when full- 

 grown : they feed ravenously on the under-side of the leaf. 

 When frightened by any shock they drop off, hanging by a 

 silken cord, which they use to regain the leaf when the 

 supposed danger has passed. In from four to five weeks the 

 larvfe are mature, and then spin a network-like tube of loose 

 yellowish silk on the leaf, blocking up one end with their cast 

 skin and covering the other with a few threads. Inside a 

 black and greyish-white pupa will be found. As pupre they 



Fig. 109. — Diamond-back Moth {PhUella 

 maciUipeiinis). 



Jlotli, larva, aud cocoon (nat. size, and magnified). 



