386 



AN ECONOMIC ENTOMOLOGY. 



the little fellows everywhere, infesting almost all kinds of insects, 

 and undoubtedly they do much to prevent the increase of injuri- 

 ous species. Especially is this true of those ovipositing in eggs 

 of other forms, for they are then "nipped in the bud," so to 

 speak. Their work in the destruction of scale insects is also of 

 great importance, and frequently we find on a scale-infested tree 

 a large proportion with little round holes, showing where a para- 



FiG. 445. 



Fig. 444. 



Tricliogramma pretiosa, a parasite in insect eggs; a 

 dot may represent natural size. 



Female hosoma oviposit- 

 inK in stem of wheat. 



site has emerged. It is a pity that in a family so generally useful 

 we should find, exceptionally, some injurious species ; but there 

 is no doubt that members of the genus Isosojna lay their eggs in 

 the stems of grasses, including wheat, and the larvse, working as 

 they do in the joints, have received the name "joint- worms." 

 The stem hardens where the larva punctures it, and this inter- 

 feres with the nourishment of the plant above that point, les- 

 sening or entirely preventing the formation or maturing of the 

 grain. There is but a single annual brood of these insects, and 

 the winter is passed in the straw, from which the adults emerge 

 in spring. In localities where this insect is sufficiently abundant 

 to make it necessary to use remedial measures, the utilization of 



