THIRTIETH REPORT OF THE STATE ENTOMOLOGIST 



19 



which was more than compensated for after June. During that 

 month there was an excess of precipitation when compared to the 

 average; in fact, some weather stations recorded a new maximum 

 precipitation for June. This would lead one to believe that there 

 was possibly a similarity between conditions in eastern Montana 

 in 1944 and the midwest areas where the Hessian fly is constantly 

 a threat to wheat, and that the excess precipitation of the past 

 year brought on the infestation. In referring back to the 1924 out- 

 break, however, this is not immediately apparent. For the State 

 as a whole the year 1924 was dryer than usual. For weather sta- 

 tions in the infested area there was no striking deviation from 

 the average during the growing-season months. There is a sim- 

 ilarity, however, between the years just preceding 1924 and those 

 just before 1944. The growing season precipitation (April to August 

 inclusive) for 1919 was very low, a little over four inches. The 

 1920 season approached the average for these months, and more 

 than average precipitation fell during the growing seasons of 

 1921, 1922, and 1923. The years just before this latest infestation 

 were also years of greater than average precipitation during the 

 growing season. Nineteen hundred and thirty-nine was less than 

 average by about an inch. During 1940 the precipitation was 

 average, and during 1941, 1942 and 1943 there was more than aver- 

 age rainfall. In examining 

 J >M Mf on ly the one factor of precipi- 



iH tation, these data would indi- 



cate that the two obvious out- 

 breaks of the Hessian fly have 

 followed three seasons of 

 more than average precipita- 

 tion and have been sufficient- 

 ly great to be noticed on the 

 fourth. It would not be accu- 

 rate to state that this is the 

 only factor affecting the in- 

 crease of this pest nor can we 

 state that the Hessian fly out- 

 breaks will always follow pre- 

 cipitation conditions outlined 

 above. It is very probable that 

 it is present in Montana every 



,„ year but that it expresses it- 



Fieure 5. Hessian fly. Shows "flaxseed" J 1£ . . r , ,. 



6 ^ . , , \. ^ self in injurious populations 



pupae in typical location just above the ■. u J j , . r ■ 



p p " * e ' , i only when condit ions are 



nodes. Somewhat enlarged. * - , .,, 



& proper for a build-up. 



The Hessian fly is a small, weak midge, and is seldom noticed 



in the field. Its eggs are laid on the leaves of the wheat plant, 



