ECONOMIC ENTOMOLOGY 313 



mental if the insect feeds upon the plant or animal or inter- 

 feres with its successful existence. It is beneficial, if it 

 contributes to its success by warding off other dangers or 

 assisting pollination or contributing in any way to its better 

 growth and development. 



ECONOMIC ENTOMOLOGY. 



Economic entomology is based upon the relation of 

 insects to mankind and all species that interfere with his 

 welfare are considered injurious, and those that may serve 

 him in any way are considered beneficial. The relation, 

 however, may become very complex. An insect that feeds 

 upon a cultivated crop, or destroys the products of a crop, 

 or injures a domestic animal, or worries man himself, or 

 menaces his health by inoculating him with disease, is 

 injurious from the human stand-point. While if it produces 

 a valuable material such as silk or honey, wax, dyes, etc., 

 or serves to destroy injurious species as predaceous and 

 parasitic forms, or feeds upon noxious plants, weeds, or dis- 

 poses of noxious substances, as the scavengers, it is directly 

 useful, and we term it beneficial. Many cases are very clearly 

 in one class or the other; many have little apparent impor- 

 tance one way or the other, and in many cases the relation 

 may change with circumstances. For example, a parasitic 

 insect preying on an injurious species is useful to us, but if 

 it destroys a useful insect it becomes injurious. A parasite 

 on a parasite, that is, a secondary parasite is detrimental if 

 the primary parasite attacks an injurious insect, and a 

 parasite upon this secondary parasite, that is, a tertiary 

 parasite would be useful, since its effect would be to check 

 the secondary and favor the ])rimary parasite. Still further, 

 a quaternary parasite, and this is I believe as far as this 

 relation is known, would be injurious. The reverse in each 

 case would be true if the original host were useful. 



We should not forget that these three terms refer strictly 

 to mankind, for in the broader biological sense each kind of 



