376 



COLLEGE ZOOLOGY 



d. The Economic Importance of Insects 



The economic importance of certain insects has been em- 

 phasized during our discussion of the orders of insects. A few 

 species of insects are of considerable value to man. For example, 

 the honey-bee produces enormous quantities of both honey and 

 wax; the silkworm supplies us with delicate silk threads; the 

 bees and many other insects cross-fertilize flowers; the bodies 

 of the scale insect, Coccus cacti, are known as cochineal ; pre- 

 daceous species usually prey upon injurious insects; and many 

 parasitic species attack destructive caterpillars. 



On the other hand, the injurious insects are numerous and im- 

 portant. Some of them are responsible for the transmission of 

 certain diseases. For example, the house-fly carries the germs 

 of typhoid, tuberculosis, cholera, and many other diseases on its 



TABLE XIII 



ANNUAL LOSSES DUE TO INSECT PESTS OF THE UNITED STATES 



