AGRICULTURE. 



Kig. 39. Caterpillar covered with 

 parasites. 



In the case of house plants, garden plants and orchard trees 

 we can wash and spray with solutions that destroy the lice, but 

 with lice that injure the grain such means are not yet practi- 

 cable. Why then do not the lice multiply so as to eat up 

 everything in the fields? Simply because there are other insects 

 that keep them in check. There are some tiny flies that 

 attack the lice and lay their eggs 

 right in the bodies of the lice. 

 These parasites soon kill the lice. 

 Other insects are destroyed in 

 the same way, such as cater- 

 pillars and grasshoppers. If 

 we carefully examine the leaves of trees or other plants 

 infested with lice we may find some of the beautiful little 

 lady-beetles and their larvae feeding upon the lice. Another 

 enemy of lice is the aphis-lion, the larva of a lace-wing fly. 



FLIES If you examine a common house-fly or a mosquito, 

 you observe that it has only two wings. Here then we have 

 another order, that of the "two-winged" flies, known as diptera. 

 The Hessian fly, the wheat midge, the many flies of root plants, 

 mosquitoes, fleas, and many of the flies that annoy stock all 

 have two wings only and belong to this order. 



The Hessian fly appears in spring as 

 a small winged insect with long legs. 

 The female lays about twenty eggs in 

 the fold or crease of the leaf of the 

 young wheat plant. After a few days the 

 larvae hatch and get down between the 

 stem and leaf-sheath. Here they feed 

 on the plant and weaken it so that 

 the heavy head soon after topples over 

 and the grain is destroyed. The eggs 

 may be laid either in the spring or in 

 the early fall. When the latter is the 



Fig. 40 The Hessian fly 

 two-winged insect. 



