26 



TRANSITION ZONE. 



The species occurs well up in the Transition zone, if not indeed 

 overlapping on the southern limits of the Boreal zone, though in this 

 northern latitude it is apparentl}^ not ver}^ destructive. It is here 

 recorded as injurious to late sweet corn and also tomatoes. Rather 

 severe injury was reported in the vicinit}^ of London, Ontario, in 1898, 

 by Dr. James Fletcher," and also by Mr. J. De^rness.* Several fields 

 of corn were infested, varying in extent from about 20 to 95, or in 

 one case nearly 100 per cent, with from one to several larvae in each 

 ear. In a letter concerning this species Doctor Fletcher states: 



Heliothis armiger [obsoletci] is sometimes abundant and destructive to late sweet 

 corn, the larvae at that time being of all sizes to full grown. ^ * * Moths are out 

 at Toronto and here [Ottawa] by the end of September and sooner. * * * We 

 have also received specimens from Beulah, Manitoba, but the species is decidedly 

 not common. 



Injury to sweet corn in 1892 is reported^ from Farmington, Me., a 

 town on the border line of the Boreal and Transition zones in that 

 State. The identity and character of the insect seem to have been 

 quite unknown to those suffering from its ravages, which may be 

 taken as evidence of its infrequent occurrence. No records have been 

 found to indicate its occurrence in the numerous patches of the Boreal 

 zone along the Allegheny and the mountain chains of the West, 

 although it is known to occur in numbers in adjacent areas of the 

 Transition zone. It may, therefore, perhaps be safel}^ inferred that 

 the insect is not able to extend itself permanently^ into the Boreal 

 zone, by reason of temperature and other conditions. 



It is pertinent to mention that in New Mexico Prof. T. D. A. 

 Cocke rell, who has given considerable attention to the life zones of 

 insects, records^ the species only from the area designated by him 

 Upper (including middle) Sonoran. 



The restraining influence of low and sudden changes in temperature 

 on the successful existence and increase of species of more southern 

 occurrence, in their northward spread, has been recentl}^ commented 

 upon^ b}^ Doctor Chittenden, of this Bureau. According to this gen- 

 tleman's observations the boUworm was comparatively rare on corn 

 and other crops, which it commonly infests in the vicinity of Washing- 

 ton during the season following the severe freezes of Februar}^ and 

 March, in 1899. The severe character of the winters of the more 

 northern States, coupled with the relatively low sum of effective tem- 

 perature, no doubt has an important bearing on the comparative 

 immunity of this territory from serious injury. 



«Eept. Ent. Soc. Ont, 1898, p. 82. 



ft Ibid., p. 62. 



cAnn. Kept. Maine Agric. Exp. Sta., Pt. IV, 1892, p. 119. 



(iBul 24, N. Mex. Agric. Exp. Sta., p. 35. 



«Bul. 22, n.s., Div. Ent., U. S. Dept. Agric, p. 56. 



