October, ’23] 
CARTWRIGH 1 : HESSIAN FLY EMERGENCE 
433 
normal conditions of temperature and rainfall were the primary causes of this delayed 
emergence. Normal emergence consisted of two small waves on September 22 and 
30 respectively, from which progeny developed normally. The heavy delayed 
emergence occurred October 27 to 30 from which progeny struggled through the 
winter with at least a 25% death rate. Infestation by progeny of the late emergence 
caused total loss of 24% to 38% of wheat plants sowed on the usual recommended 
dates and some injury to an additional 24% to 37%. 
The emergence of the Hessian fly (Phytophaga destructor Say) wherever 
it occurred throughout the East Central States in the spring of 1922 was 
normal. The fall emergence for this territory occurred as partially 
regular and in certain areas markedly irregular. This irregular or de¬ 
layed emergence was centered within the triangular area bounded roughly 
by the Mississippi and Ohio Rivers and a line drawn eastward from St. 
Louis, Missouri. It is intended to review the climatological conditions 
existing from the time of the regular spring emergence to the delayed 
fall emergence and to discuss the behavior and economic aspect of the 
latter. 
Climatological data of the U. S. Weather Bureau for Illinois and In¬ 
diana, the states invaded by the irregular fly brood, show that for July 
the average temperature was almost normal. For August in Illinois 
the state average of temperature was not unusual but precipitation was 
the least since 1897, the deficiency being as much as three inches in 
places. In Indiana the mean August temperature was slightly above 
normal and precipitation deficient. September in Illinois was warm 
and dry with more clear weather than any year since 1897. Deficiency 
in rainfall ranged from one to four inches south of the Illinois River with 
practically no rainfall after the 20th. Temperature in Indiana for 
September was above normal and precipitation deficient and with minor 
exceptions practically no rainfall after the 20th. For both Illinois and 
Indiana October opened with high temperatuie. For Illinois tempera¬ 
ture was 10 to 14 degrees above normal from the first to 6th, 10 degrees 
below normal from the 12th to 17th, and 12 to 18 degrees above from 
27th to 31st. For Indiana the second decade was colder and killing 
frosts occurred in nearly all counties on the 13th, followed by recurrences 
on the 18th to 20th. The last week was much above normal. Rainfall 
for both Illinois and Indiana occurred within periods 6th to 11th, 13th 
to 16th, and 22nd to 23rd and none for the remainder of the month. 
The activity of the Hessian fly was continuously observed at Centralia, 
Illinois and the following data compiled from the records of this place. 
Drouth was temporarily broken by rainfall on September 10th and 19th, 
a total of .6 inch. Almost coincident with this period of moisture, adult 
Hessian flies appeared September 22nd and represented the first wave of 
