376 



AN ECONOMIC ENTOMOLOGY. 



Fig 



the wood dries, becomes unsuitable for food, and, as the insect is 

 incapable of travelling, it starves to death. 



In the case of Cephus pygrnceus, the insects boring in wheat, 

 they spend the winter either low down in the infested stalk — i.e., 



in the stubble — or in the soil just 

 below the surface, in either the 

 larval or pupal condition. The 

 ])roper remedy is to burn the 

 .stubble as soon after harvest as 

 possible, or to plough it under 

 deeply. This destroys the in- 

 sects and results in preventing 

 injury the year following. We 

 have no means of reaching the 

 larva while it is actually working 

 in the stem of the plant. The 

 remedy is radical, and were it 

 universally resorted to, would 

 need to be applied only at inter- 

 vals of several years. 



The "gall-flies," belonging to 

 the family Cynipidcs, are curi- 

 ous creatures. They resemble 

 minute wasps in form, and gen- 

 erally have a very short, chunky 

 body, which is often compressed 

 and joined to the abdomen by a very slender petiole or stalk, 

 in sharp contrast to the species heretofore written of These 

 gall-flies are mostly true parasites on plants. They derive their 

 common name from the fact that they produce swellings, protu- 

 berances, or "galls" of great variety on vegetable tissues ; some- 

 times on leaves, on twigs, on trunks, or even on roots ; and 

 perhaps, of all others, the oak is the favorite of the insects of 

 this family, bearing the greatest variety of galls on all its parts. 

 I say these insects are mostly plant parasites, and intend to ex- 

 press by this that they do not actually eat the infested vegetable 

 tissue. The irritation caused by the larva induces an abnormal 

 growth in the part of the plant infested, and in a cell in this 

 growth it has its home. Here the insect reaches maturity with- 



Cephus pys;m(sns, wheat-stem saw-fly. 

 — a, outline of larva, natural size ; b, 

 larva enlarged ; c, larva in wheat stalk, 

 natural size ; e, adult female ; f, female 

 parasite, enlarged. 



