August, '08] JOURNAL OP ECONOMIC ENTOMOLOGY 257 



crn Ohio, last May, its almost entire absence has been reported in lo- 

 calities where last year it was clisastronsly abundant."^ Later Pro- 

 fessor Webster stated- that it "had spread at one time as far north 

 as Chicago, 111., and had almost reached the shore of Lake Erie in 

 Ohio. A very severe winter, however, had killed it off in southern 

 Illinois and Ohio, and it has not recovered this lost ground, and 

 might not again in years." It probably still occurs in extreme south- 

 ern Ohio according to Prof. H. A. Gossard and was noted by Professor 

 Webster in 1901. Doctor Chittenden^ noted its scarcity in Washing- 

 ton, D. C, in 1899, foHowing a minimum of — 15°F., and the writer 

 made the same observation in Delaware. This was the lowest tem- 

 perature which had been experienced at Washington for over twenty 

 years. As it was accompanied by heavy snow, the harlequin bug was 

 largely protected from the severest cold, otherwise it would doubtless 

 have been exterminated. 



The harlequin bug emerges from hibernation at Newark, Del., 

 about May 1, when the temperature is about 55°F. In midsummer, 

 at 74°F., the life cycle there occupies about one month. The life 

 cycle thus consumes 1236°F. over 43°F. At Durham, N. H., there is 

 2925 °F. over 43° from the middle of May to the middle of Sep- 

 tember, during which time the mean is over 55°F., and according to 

 Merriam's law the species might exist -there wdth two generations. 

 But even if we take 55° as the critical point, there is required but 

 726° for a life cycle in Delaware and there is available 1119° at Dur- 

 ham, N. H., enough for one brood. But the harlequin bug does not 

 occur north of Long Island, N. Y., and is not spreading there. The 

 northern limit of this species follows the average annual-minimum 

 isotherm of 0°F. (map 2) much more closely than the Upper Austral 

 Zone. It may yet migrate to northern Ohio and Ontario, but further 

 progress seems doubtful. 



The Cotton Boll Worm or Corn Ear Worm {Heliothis ohsoleta 

 Fab.) is injurious throughout the upper and lower Austral zones, but 

 only exceptionally in the transition. It has been injurious at Lon- 

 don, Ont., near Boston, Mass., in 1894, and rarely in Michigan. It 

 does not winter in Minnesota and no records of injury occur in Da- 

 kota, ]\Iontana or Wyoming.* Professor Quaintance remarks, "The 

 severe character of the winters of the more northern states coupled 

 with the relatively low sura of effective temperatures, no doulit has 



iBulletin 20, Bureau of Entomology, U. S. Deyt. Ayr., p. 72 (1899). 

 2Bulletin 60, Bureau of Entomology, U. S. Dept. Agr., p. 130 (1906). 

 sBulletin 22, n. s., Division of Entomology, U. S. Dept. Agr., p. 55. 

 •^Bulletin 50, Bureau of Entomology, U. S. Dept. Ai;r., p. 26-27. 



