290 Proceedings of Indiana Academy of Science 



pests are of foreign origin. These are not necessarily pests of prime 

 importance in their native home but brought here and finding favorable 

 breeding places with the absence of their natural enemies they are 

 capable of increasing with scarcely any restriction. Notable examples 

 include the Hessian fly, San Jose scale, Oriental peach moth, currant 

 worm, cabbage maggot, cabbage worm, wheat midge, European corn 

 borer, gypsy and browntail moths, Japanese beetle, cotton boll weevil, 

 pink bollworm and elm leaf beetle. Even within our own country trans- 

 portation has had a marked influence on the spread of insect pests. 

 Thus the San Jose scale, first introduced into America at San Jose, 

 California, from China, was carried on shipments of nursery stock, 

 across the entire continent to New Jersey, from which place it was soon 

 distributed on plants to many other sections of the country. 



4. The reduction of certain insectivorous birds and mammals is no 

 doubt a factor in the abundance of insects. Increase in population, re- 

 duction of forests and hunting have had their influence on the numbers 

 of useful birds and mammals. 



Insects are grouped from the .standpoint of control in several ways. 

 From the point of view of control by insecticides, they are usually 

 grouped according to the type of mouth parts, i. e., those with suctorial 

 and those with mandibulate mouth parts. From the agricultural stand- 

 point it is desirable to class insects as monophagous (restricted to a 

 single host), oligophagous (dependent on several, usually related species 

 of plants), and polyphagous (feeding on many species of plants). Mo- 

 nophagous insects are usually the most uniformly destructive but prob- 

 ably more readily controlled and ai'c usually more amenable to control by 

 good farm practices. These and other groupings are adopted occa- 

 sionally for specific uses and while arbitrarily arranged they serve a 

 useful purpose. 



Before proceeding with a discussion of insect control problems I 

 wish to call attention to the fact that all insects are not harmful. For- 

 tunately many are directly or indirectly beneficial. Of all described in- 

 sects approximately half or 225,000 are phytophagous, feeding directly 

 upon the tissues of various plants. Of course, only a small percentage of 

 phytophagous insects affect cultivated crops or plants useful to man but 

 even in recent years many which originally attacked only wild hosts have 

 gone over to cultivated crops and we may anticipate increasing numberr 

 of such transfers. Of the remaining 50 per cent, most of which are bene- 

 fiicial, about 30 to 35 per cent are parasitic or predaceous on other in- 

 sects, probably 17 per cent are scavengers, a comparatively small number 

 are beneficial as producers — honey-bee and silk worm — and a few, prin- 

 cipally bees and similar nectar-feeding species, as pollenizers. 



Practically all insect contiols are based on our knowledge of the 

 structure, life history and habits of the insect in question. For con- 

 venience we may divide methods of control into two main groups and 

 each of these into smaller groups. 



I. Natural Controls 



a. Climatic controls 



b. Natural enemies 



