400 ECONOMIC ENTOMOLOGY 



eggs, larvae, or adults of insects such as the tobacco and tomato worms 

 {SphingidcB), corn ear worm, potato beetle, celery caterpillar, white 

 grubs, cabbage butterflies, asparagus beetles, etc. 



Again, it is often wise to cut out, burn, or otherwise destroy certain 

 insects whenever they appear. For example, web-worms, tent-cater- 

 pillars, stalk-borers, etc., may be effectively dealt with at certain stages 

 in this way. 



Sometimes, too, under certain conditions, insects can be controlled 

 by jarring and beating the infested plants. When poisons are objec- 

 tionable, this method of dealing with potato beetles, currant worms, 

 plum curculio, etc., is recommended. 



lo. High and Low Temperatures 



In flour or meal mills it has been practicable to raise the temperature 

 to 120° or 125° for 6 to 8 hours, when it is found that all the insects — 

 eggs, larvae and adults — are killed. On the other hand insects are not 

 able to develop at cold-storage temperatures, hence products kept in 

 cold storage are kept free from injury. 



THE ACTION OF INSECTICIDES 



(Consult Tech. Bulls. 11 and 21, Mich. Agric. Coll.) 



Until recently the mode of action of insecticides was not well under- 

 stood. It was commonly stated that contact substances kill insects 

 by stopping the breathing pores or plugging the tracheae, producing 

 death by suffocation. Recent investigations, however, go to show that 

 insects are not readily suffocated. The death-producing action of 

 chemicals is mainly due to their absorption into their tissues. The 

 volatile portions of kerosene, carbon bisulphide, gasoline, creolin, pyr- 

 ethrum, etc., are effective long before the liquids have time to pene- 

 trate the chitin or the spiracles into the tissues. 



With the penetration of the volatile substances the nervous system 

 is seriously affected, and results resembling narcosis are produced, 

 where there is a disturbance of the respiratory activity. Insect 

 tissues soon become saturated when exposed to the vapors of the 

 substances mentioned, and death ensues through the inability of the 

 tissues to absorb oxygen in the presence of these vapors. 



