THE COLEOPTERA 117 



On small areas, Paris green dry, mixed with 10 to 20 parts of some 

 inert material, dusted over the plants, preferably while the dew is on 

 them, is a fair treatment, and this poison as a spray can also be used. 

 Arsenate of lead is at present the preferred poison for this pest, however. 



Various birds, skunks, snakes and toads feed on the Colorado Potato 

 Beetle to some extent, and it also has numerous insect enemies. 



The history of the development of the Colorado Potato Beetle, from 

 an unimportant, even probably a rather uncommon insect, feeding upon 

 a plant of no value to man, into one of the most abundant and widely 

 distributed of our pests, attacking and seriously injuring an important 

 crop, is a suggestive one. In a division of the insects of the United 

 States into those which are injurious as regards man and his various 

 interests; those which are beneficial, and those which are of little or no 

 economic importance either way, we shall find that the last group is by 

 no means a small one. How many species in this group are there which 

 are potential pests? It is true that the making available of a new food 

 plant to which the Colorado Potato Beetle could turn, was probably the 

 chief factor in this particular case, but any insect which for some reason 

 changes from an unimportant food plant to a crop plant may at once 

 become a pest. Thus another Chrysomelid only a little smaller than the 

 Colorado Potato Beetle and closely related to it, the Three-spotted Do- 

 ryphora (Doryphora divicollis Kirby) , which feeds on milkweed) is now of 

 practically no importance. But if it should change its food to some 

 valuable crop plant it would at once become an important addition to 

 the list of insect foes man has to combat. Several such cases are al- 

 ready known. How many others may appear as the changing conditions 

 which always accompany an increasing population and the consequent 

 changes in plant population take place, no one can predict. Some species 

 of plants once common are rapidly disappearing. As they go, will the 

 insects feeding on them go too, or will they be able to find another food 

 plant, and will this one be of value to man? The appearance of new 

 pests in such ways may come at any time, and the fact that an insect is 

 not now a pest should not lead to its being ignored, for it may have great 

 potential importance. The Murky Ground Beetle (Harpalus caliginosus 

 Fab.) is now mainly a carnivorous beetle, but sometimes, though rarely, 

 attacks the strawberry. If it should turn to this latter plant entirely 

 for its food, another important pest would be added to our list and lost 

 from among our friends. 



Such facts call for as complete a knowledge as possible of the life 

 and habits of all insects whether now beneficial or only of no economic 

 importance, in order that we may have the knowledge of them and 

 their ways which is necessary in case they should become injurious. 



