380 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



forms upon which we depend for pollination of plants and other useful 

 functions. We are frequently told of the killing of colonies of bees 

 through the use of sprays for the control of fruit and crop pests, and 

 we are consequently urged to have more regard for the life of the useful 

 insects even though the injurious forms may in some instances do 

 more harm. These warnings and admonitions are, of course, well 

 meant and should be given every possible consideration. There are 

 as usual two sides to these arguments. A recent article in one of the 

 leading bee publications referred to the warning given by entomolo- 

 gists of the possible grasshopper outbreak the coming season and 

 indicated that grasshoppers were very abundant in most of the sweet- 

 clover regions the past season. It was pointed out that the sweet- 

 clover is one of the favorite honey plants for the honeybee and that 

 the invasion of grasshoppers might well prove serious to the beekeeper 

 since sweetclover is attractive to the grasshoppers as a food and is the 

 sole source of surplus honey in a large area. Of course, the obvious 

 answer is to heed this particular warning and poison the grasshoppers 

 to save the food for the bees, and since grasshoppers can be poisoned 

 with a material which is not attractive to the bees, there can be no 

 argument as to what should be done. 



It is necessary to treat of insects when controlling and eradicating 

 many of the plant diseases. The Dutch elm disease, introduced from 

 abroad and now constituting a serious threat to the elms of this 

 country, is spread by at least two insects and possibly by more. 

 Sugarcane mosaic is carried by insects. The most important disease 

 of sugar beets, curly top, is spread by leafhoppers. It is suspected 

 that phony disease of the peach may be spread by insects, although 

 definite information on this point is lacking. It has recently been 

 found that peach yellows is spread by an insect vector, and no doubt 

 insects enter into the general program of plant-disease spread and 

 control more than we know. Insects themselves are affected by 

 diseases, and attempts are being made to develop and culture the 

 diseases with a view to using them in the fight against injurious insects. 



Treating of insects through studies of plant resistance has its place 

 in the picture. Man is limited in his consumption of many members 

 of the plant kingdom because of their bad taste, poor quality as food, 

 fibrous composition, poisonous character, or possibly even because 

 they present an unattractive appearance. Investigations by ento- 

 mologists have revealed that insects such as the hessian fly also 

 have food preferences and limitations in selection of varieties of wheat 

 or even the individual wheat plants for food. Some plants are entirely 

 unsuited for the support of the flies, even when the variety is generally 

 suitable, and parent flies selecting such plants for egg laying doom 

 their offspring to an early death. Other plants may be quite un- 

 attractive for egg laying and thus escape infestation. Study of these 



