THE DIAMOND-BACK MOTH. 259 



is blunt, and shaped like a cavalry sword with a curve upwards. 

 All this, however, is only the sheath ; this sheath is composed of 

 two halves, which open at the base, like the arms of the letter V- 

 Between these arms is the real ovipositor, brown, polished, and 

 pointed. I was able to examine the real ovipositor only by 

 drying the insects ; the muscles controlling the sheath were then 

 contracted, the sheath opened and the ovipositor was exposed.* 



(2). Much less abundant than No. 1. Same size. Head, 

 thorax, and body black ; under side of body yellowish green. 

 Legs russet-brown. Long black antennse the length of the body 

 and curving upwards, not smooth, but knotted. Wings trans- 

 parent, nervures black, not so rounded as in No. 1. The wings 

 reflect the same beautiful tints, chiefly pale green. The ovi- 

 positor is shaped like a small y, the right arm of the letter being 

 at least twice the length of the other ; it is attached under the 

 abdomen, as in No. 1, but by each of the arms. 



The moth emerges at one end of the cocoon, leaving hardly a 

 trace of exit ; the ichneumon saws an ugly round hole through it 

 near the end. 



Such is a description of some of Nature's agents, and in their 

 operations lies apparently an exhibition of Nature's plan. The 

 ichneumons, the birds, the climatic helps, only clear off a portion 

 of these pests. Man is evidently expected to investigate, to help 

 himself, and to look upon these natural aids as allies. Looking 

 through tbe letters of my correspondents, I find that, where the 

 birds were properly looked after, P. cruciferarum has been least 

 hurtful. On the other hand, where the birds have been deci- 

 mated, there the scourge has apparently been most conspicuous. 

 As an illustration, a correspondent from " an anti-rook uud bird 

 district" speaks of "whole fields having been stripped " by the 

 caterpillar, and of such spectacles as *' nearly a dozen crows and 

 a sparrowhawk nailed to a tree through the head." 



Sometimes the diamond-back is eccentric in its ravages. A 

 twenty-four acre field in Lincolnshire, where, by the way, the Act 

 for the Preservation of Birds is strictly enforced, had eleven acres 

 white turnips and the remainder swedes. " The whites," says 

 my correspondent, " were entirely ruined, but the swedes were 

 untouched. As soon as the pest was discovered the crop was 

 ploughed in," rape or late globes, I suppose, being afterwards 

 sown. 



Passing by compensation from the State for reasonable loss 

 as a matter more for the agziculturist and the politician, the 

 following remedies from my own correspondents may be offered 

 as matters of greater interest to the entomologist : — 



(1). Fields should be kept clear of cruciferous weeds, such as 

 the well-known yellow-flowering "kale"; fences, refuse-heaps, 

 headings, and vacant spaces sliould not be forgotten. (If I 

 • Doubtless Limneria gracilis, Grav. — E. A. F. 



