February, '17] McCOLLOCH: HESSIAN FLY SPREAD 163 



in wheat fields where the possibility of fly infestation had seemed prac- 

 tically negligible. In some cases these were fields planted on corn land 

 and far removed from other wheat fields. In numerous cases they 

 were fields planted according to the best approved methods for con- 

 trolling the fly. In still other cases infestations occurred where one 

 farmer would lose most of his crop while his neighbor would suffer 

 only slight injury. Investigations of many of these infestations sug- 

 gested the possibility of some factor, such as migration, as entering 

 into the problem of control. 



Previous References to Migration 



The fact that the Hessian fly does migrate has long been recognized, 

 but has been given little consideration and apparently has not been 

 taken into account in devising methods of control. 



Osborn (1898, p. 11) says, ''The powers of flight possessed by the 

 Hessian fly are sufficient to provide for its ready dispersal over limited 

 areas, and where there are continuous or slightly separated plantings 

 of wheat, rye, or barley, no other means of dispersal need be sought." 

 Further on he says that there is little tendency for the adults to 

 leave the field. 



Marlett (1900, p. 2) writes, "The migrating and scattering brood of 

 adults is the one developed in the fall; the spring brood does not wan- 

 der much from the field in which it is developed." 



Roberts, Slingerland and Stone (1901, p. 256) state that the migrat- 

 ing brood is developed in the fall and that the spring brood is less apt 

 to scatter. They go on to say that the flies can doubtless readily fly 

 to nearby fields and, by the aid of strong winds, they may be carried 

 comparatively long distances. 



Garman (1903, p. 220) says that there appears to be something like 

 a spring migration of adults from the early sown wheat to the younger 

 more succulent wheat of late plantings. 



Headlee and Parker (1913, p. 135) cite a case of apparent wind diffu- 

 sion covering about one-half mile and go on to state that "while the 

 studies . . . have shown clearly that the fly sometimes does 

 migrate this way as far as half a mile, investigations at this station 

 and elsewhere show that spring migration in sufficient numbers to do- 

 serious damage is rare and that wheat sown on clean land late enough 

 to escape the fall brood is practically never seriously injured." 



Headlee (1915, p. 5) writes, "It is frequently said by a grower that 

 there is no use to undertake fly control because some of his neighbors 

 will fail to do their part and the fly which they fail to destroy will 

 render his efforts useless. In some instances studies have shown that 

 this is partly true, but the great mass of experience does not only fail 



