INSECTS INJURIOUS TO WHEAT. 105 



cause a serious mortality to the earlier stages of the fall 

 brood of adults; and a rainless August often retards the 

 emergence of the flies until even our latest-sown wheat (in 

 Xew York) is up and ready to receive their eggs. Just such 

 weather conditions occurred in New York in 1900 and, we 

 believe, were largely responsible for the fact that in many 

 cases late-sown fields were as badly infested as those sown 

 earlier/' If there be a normal rainfall in August, the flies 

 will emerge as usual early in September and will lay their 

 eggs on volunteer, early-sown, and trap strips of wheat, 

 and late sowings will largely escape. 



Dr. A. D. Hopkins has recently worked out a most 

 valuable law governing the time of appearance of this pest, 

 and from which he has deduced a rule for '^the approxi- 

 mate determination of normal dates for the ending of the 

 fall swarm of the Hessian Fly in any locality " in West 

 Virginia. "Take a knowm normal date of a place, of 

 known latitude and altitude, correct this date to a corre- 

 sponding date at sea-level, by adding one day to each one 

 hundred feet of altitude above sea-level; then for any place 

 north of this sea-level base subtract one day for each one- 

 fourth degree of latitude and one day for each one hundred 

 feet of altitude at the place to be determined, and for all 

 points south add one day for eacli one-fourth degree of 

 latitude and subtract from the result, as before, one day 

 for each one hundred feet of altitude. The resulting date 

 will be the approximate normal. 



. " To give an example of this method of determining 

 normals, and to demonstrate its value, we will take, as the 

 most important and reliable data, the results obtained by 

 Prof. Webster, by actual experiments and observations, at 

 Columbus and Wooster, Ohio. He found that the normal 



