6 



SPRAYIXG CROPS 



seared, as if scorched by fire. These worms continue 

 feeding for several weeks before becoming full 

 grown ; they then descend to the ground, burrow into 

 the soil a short distance, and spin silken cocoons, 

 within which they change to the pupa or chrysalis 

 state and later emerge as moths. The two sexes of 

 the moths differ greatly: the male (a) has large, well- 

 developed wings, while the female (&) is wingless. 

 The latter is of an ash-gray color. On emerging from 

 the chrysalis, she crawls to the base of the tree, and 

 ascending the trunk, deposits eggs on the twigs or 

 branches of the tree. 



The Canker Worm, with nearly all other leaf-, 

 eating caterpillars, falls an easy victim to the spraying 

 machine. 



FEEDING HABITS OF INSECTS 



Insects take their food in two ways : some bite 

 and others suck. The three species mentioned under 

 the last heading are examples of those insects which 

 take their food by biting, piece by piece, the tissues 

 of leaf, stem, or fruit of their host-plant. Because of 

 this they may be destroyed by placing particles of 

 poison upon the surface of the plant. A large pro- 

 portion of the injurious insects have such biting 

 mouth-parts ; but there is also an important class 

 w^hich have instead of jaws a pointed beak that they 

 push into the cells of the plant, and suck out the sap. 

 Insects of this kind cannot be destroyed by coating 

 the food-plant with particles of poison, for such par- 

 ticles will not enter their alimentary system ; conse- 

 quently, one must use against them some insecticide 

 which kills by contact, either affecting the general 

 surface or reaching the interior through the breathing 

 tubes. The former are called Contact Poisons and 

 the latter Tracheal Poisons. Kerosene is the most 



