INSECTS INJURIOUS TO AGRICULTURE 359 



have elsewhere insisted upon the fact that one of the measures most 

 often recommended — the destruction of the stubble remaining in the 

 field after the harvest — may have unfortunate consequences, for doing 

 this in a tardy manner one risks intervening at a moment when all 

 of the flies have emerged and have abandoned the stubble, exposing 

 to destruction only the parasites whose part would have been to stop 

 the invasion the following year. 



Ivieffer has pointed out a remarkable analogous fact for a 

 Cecidomyiid, namely, Diplosis tritici, attacking not the stubble, but the 

 grains of wheat, and has shown that one of the measures which has 

 been advised — burning the debris after the threshing — has only an 

 injurious effect, for while it is true that this debris contains pupae of the 

 midges, it should be remembered that the healthy and nonparasitized 

 larvas of these flies transform in the ground, while those which remain 

 in the heads are, on the contrary, parasitized. 



In the cases which we have just mentioned, the protection to be 

 accorded to the parasites consists solely in abstaining from inoppor- 

 tune measures capable of bringing about their destruction without any 

 advantage whatever. In other cases it is an active protection which 

 has been advised, and which comprises operations destined to insure 

 the survival of the parasites. 



It is in this way, for example, that Decaux, struck by the multi- 

 tude of ichneumon flies, or Braconids, which came out of the buds of 

 apple attacked by Antliorwmus, advised, in place of immediately 

 burning these buds as was generally done, preserving them in boxes 

 covered with gauze, raising the latter from time to time during the 

 period of issuing of the parasties so as to permit them to escape. In 

 1880, he put this method into practise and collected in Picardy buds 

 reddened by the Antlwnomus from 800 apple trees, amounting to 

 5 hectoliters; and thus accomplished the destruction of more than 

 a million Anthonomi, and set at liberty about 250,000 parasites which 

 the following year were aids in the destruction of the weevils. The 

 orchards treated being isolated in the middle of cultivated fields, it 

 sufficed to repeat the same operation the following year in order to 

 stop all serious damage during ten years. 



This plan started by Decaux has been perfected by Berlese (1902) 

 in order to protect the parasites of the Cochylis. This author recom- 

 mends the use of boxes with the cover pierced by a window, being also 

 covered by a metal plate perforated with holes 2 mm. in width. In 

 the autumn there is placed in the box nearly full-grown larva? with 

 the leaves necessary for pupating. In the springtime the parasites 

 will issue through the openings, while the moths perish in the box. 6 



8 If it is desired to preserve the parasites for study, the perforated plate 

 is covered with a bell glass, in which the parasites accumulate without ever 

 reentering the dark box. 



