264 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 34 



The blueberry magjiot is an example of incipient species forma- 

 tion.^^ A strain attacking apples has developed and reached the 

 degree of separation so that each form can perhaps exist independ- 

 ently upon its respective host. It is reasonable to believe that man, 

 by creating genetically different strains of plants, must, in time, deal 

 with the attacks of increased numbers of physiological strains of 

 some of their insect feeders. This appears to be explained by 

 adapted strains of the insects being able to survive while unadapted 

 ones perish.^^ 



Codling moths sent from Colorado to Virginia did not behave with 

 respect to their ability to enter sprayed apples as did the codling 

 moths of Virginia. ^^ It was concluded that in this regard there were 

 different strains of codling moths in the two States. Some strains of 

 wheat lightly attacked by the Hessian fly in Kansas have been se- 

 verely attacked in Illinois.^* It is the soft wheats which furnish 

 many resistant strains in Kansas, while, according to the literature, 

 in Russia the hard wheats furnish more of these strains. The semi- 

 hard variety, Kawvale, is more heavily attacked by Hessian fly in 

 Indiana than in Kansas. 



BENEFICIAL INSECTS 



Some insects accomplish useful services to mankind and are, there- 

 fore, introduced, propagated, and encouraged by man. Here follows 

 a host of parasite introductions of the European corn borer, Japa- 

 nese beetle, gypsy moth, etc. More than 50 parasites, including 

 both native and introduced, now attack the oriental fruit moth and 

 they offer man the chief hope of control. The introductions to 

 control citrus pests have achieved notable results. Trichogramma 

 adults have been propagated and released for the control of the 

 codling moth, sugarcane moth borer, European corn borer, oriental 

 fruit moth, and the greenhouse leaf tier. The introduction of the 

 fig insect in 1901 ^^ made possible the fig industry of California. 

 While the caprification of figs is an essential part of that industry, 

 it has been discovered to be complicated by the dissemination of the 

 stem rot of these fruits. It has, hoAvever, been found possible to 

 produce these insects in the laboratory, uncontaminated by the spores 

 of this disease. 



" Lathrop, F. H., and C. B. Nickels. The biology and control of the blueberry maggot. 

 * * * U. S. Dep. Agr. Tech. Bull. 275, 76 pp., 1932. 



^ Thorpe, W. H. Biological races in insects and allied groups. Biol. Rev., vol. 5, 

 pp. 177-212, 1930. 



" Hough, Walter S. Studies of the relative resistance to arsenical poisoning of dif- 

 ferent strains of codling moth larvae. Journ. Agr. Res., vol. 38, pp. 245-256, 1929. 



" Painter, R. H., et al. Resistance of varieties of winter wheat to Hessian fly. 

 Kansas Agr. Exp. Sta. Tech. Bull. 27, 58 pp., 1931. 



" Condit, I. J. Capriflgs and caprification. California Agr. Exp. Sta. Bull. 319, 

 pp. 341-375, 1920. 



