160 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



theoretical fly-free dates in Kansas from determined dates in West 

 Virginia or Ohio. Before I came to New York to attend these meetings 

 I attended a conference on the Hessian fly at the Bureau of Entomology 

 and presented maps and tables showing how fly-free dates could be 

 computed for the entire winter wheat region of the United States and 

 Canada, and that the computed or theoretical dates agreed very closely 

 with the general dates for sowing wheat at a number of representative 

 places in each state, as taken from the bulletin on Seed-time and 

 Harvest.^ In this bulletin the dates are given on which the greater 

 number of farmers sow wheat, which is a pretty good indication as to 

 the best time to sow wheat to give the best yield in an average season 

 and at the same time be late enough to escape the fall attack of the fly. 

 The computation of fly-free dates was based on Webster's average 

 date for Columbus, Ohio, and our present law of latitude, longitude, 

 and altitude which may be defined as follows: 



All other conditions being equal the variation in the date of a period- 

 ical event in the seasonal activities of a plant or animal in North 

 America north of Mexico is at the average rate of four days for each 

 1° of latitude, 5° of longitude and 400 feet of altitude — earlier south- 

 ward, westward and descending in the spring and early summer and 

 later in the reverse directions in late summer and autumn. This gave 

 me a fly-free date of August 31 for Orono, Maine — farthest north — 

 and November 11 for southern Texas, a difference of seventy-two 

 days. After determining the theoretical fly-free dates for all of the 

 intervening states, I compared them with the general dates of sowing 

 wheat in the same section of the states and got some rather interest- 

 ing results, in showing with very few exceptions that the theoretical 

 fly-free date coincided closely with the general wheat sowing periods 

 for all localities compared. 



At Wooster, Ohio, the fly-free date is September 20 while the average 

 time for sowing wheat is September 18 or two days earlier than the 

 fly-free date. At Columbus, Ohio, the determined average fly-free 

 date is September 25, and the average date of sowing wheat is Sep- 

 tember 24. 



At Wellington, Kansas, the fly-free date should be October 10. Now 

 what is your date, Mr. Dean? 



Mr. G. a. Dean: October 12 or 13. 



Mr. A. D. Hopkins: The theoretical date misses it only about a 

 day. But October 3 is given as the best date to sow wheat. That 

 agrees pretty well, doesn't it? 



Mr. G. a. Dean: Yes, for maximum yields. 



Mr. a. D. Hopkins: For Manhattan, Kansas, we have October 5 



^Covert, James R., Seed-time and Harvest, Bui. 85, Bur. Stan., 1912. 



