2 INSECTS INJURIOUS TU VEGETABLES 



The different stages of some insects are so diverse that they 

 can be identified only by specialists, and many entomologists 

 are unable to recognize them without reference to technical 

 descriptions and illustrations. Some knowledge of the distri- 

 bution and origin of a species is of value, as well as some 

 acquaintance with its history and literature. 



A knowledge of the life history of an insect consists in 

 knowing: when, where and how its eggs are deposited; how the 

 larva feeds, and how many stages there are in this period; the 

 habits of the larva, whether diurnal or nocturnal, whether 

 omnivorous or a dainty feeder ; how and where it transforms 

 to pupa; how and where and in what stage it passes the 

 winter; the number of generations produced each year; the 

 first appearance of the insect and its disappearance, and the 

 same of each generation; its food plants, natural and culti- 

 vated, and above all, its favorite foods, both as larva and adult. 

 If to this we add a knowledge of the effect of farm practice 

 and of insecticidal and mechanical methods on the insect we 

 have, in a general manner, the main facts desired. 



We must determine in what stage and at what time the 

 insect is most vulnerable, and by practice and experiment 

 learn the best remedy. A knowledge of the appearance and 

 place of deposition of the eggs will, in the case of some 

 species, furnish means for their control, for many insects can 

 be combatted successfully merely by destroying the eggs. 

 Others may be killed in their cocoons. 



The most valuable weapon that can be used in combatting 

 an insect consists in an intimate knowledge of the insect itself 

 and its life economy, its natural enemies, its susceptibility to 

 natural influences, heat and cold, dryness and moisture, and 

 their effect upon its increase or decrease directly, or indirectly 

 by destroying or favoring the growth of its enemies. A 

 knowledge of the weeds and wild plants that furnish food for 

 these insects, in addition to cultivated plants, and the soils in 



