88 



CONTROLLING INSECTS AND DISEASES 



destroyed before the insects succumb. For the same reason, the 

 appHcation should be made at the beginning of the attack rather 

 than after considerable destruction has taken place. 



The spraying materials most commonly used at the present 

 time for the control of chewing insects are Paris green and arsenate 

 of lead. Both are compounds of arsenic. They can safely be 

 used on vegetables if they do not come in contact with the edible 

 part, or if considerable time is to elapse between the spraying and 

 the gathering of the crop for use. For crops that are to be used 

 soon after spraying, white hellebore is a safer material to employ, 

 since it is a vegetable product and loses its poisonous properties 



Fig. 48. 



-Squash bug, a sucking insect: 

 young bugs in different stages. 



, adult; b, egg cluster; c, d, 

 Twice natural size. 



after a few days' exposure to the air. It is especially useful for 

 spraying cabbage attacked by worms after heading has commenced. 

 Sucking insects do not have distinctly developed jaws like the 

 chewing insects, but are provided with tube-like, sucking mouth 

 parts (Fig. 48). They cannot bite off portions of the plant, but 

 must take their food in liquid form. Their method of obtaining 

 food is to insert the beak into the tissue of stem or leaf and suck 

 out the plant juices. When these insects attack a plant in large 

 numbers, so much juice is abstracted that the plant is seriously 

 weakened, and in extreme cases may be killed outright. It is 

 impossible to poison the food of sucking insects, since they draw 



