4 



BULLETIN 1008, U. S. DEPARTMENT OF AGRICULTURE. 



for males which are sure to emerge. Taking all of these facts into 

 consideration, success beyond expectations was achieved in the fall 

 of 1919, in making counts for the spring brood of 1920. 6 



AVERAGE NUMBER OF OVA FOR THE PRINCIPAL BROODS. 



In presenting the results of this investigation, it will be necessary 

 to consider first the average number of ova which can be laid by 

 females of the principal generations. The data for each of these 

 generations will be tabulated separately. After this has been done, 

 it will be necessary to take into consideration the proportion of the 

 two sexes before a sufficient basis can be had for estimating the rate 

 of reproduction of the Hessian fly. 



FALL GENERATION. 



In Table 1 are given the results of counting the number of ova 

 contained in 107 females. These flies were obtained from six dif- 

 ferent fields, as indicated by their cage numbers. It will be noted 

 that the average number of eggs per female varies considerably in 

 different fields, even when the number of females counted is approxi- 

 mately the same. It is thus easy to see what a difficult matter it is 

 to obtain a fair average number of eggs per female. The figures, 

 however, are as fair as could be obtained for the year in question 

 and in the time available. 



Table 1. — Average number of ova for females of the fall generation of the 

 Hessian fly, Carlisle, Pa., 1919. 



Cage No. — 



Number 

 of females 

 counted. 



Number 

 of ova. 



Minimum 



per 



female. 



Maximum 



per 



female. 



| Average 

 Range. per 

 female. 



1620 



28 

 26 

 36 

 9 

 6 

 2 



8,014 

 6,148 

 13, 422 

 1,361 

 1,099 

 658 



74 

 33 

 189 

 107 

 134 

 314 



383 

 365 

 464 

 195 

 302 

 344 



309 286.0 



1716 



332 236. 2 



1753 



275 

 88 



168 

 30 



372.8 



1755 



151.2 



1779 



183.2 



1795 



329.0 







Totals 



107 



30, 702 



33 



464 



431 



286.9 







The actual number of ova per female varies from 33 to 464, with 

 a range of variation of 431 and an average per female of 286.9. 

 It may be added that the smallest female found since this work 

 began belonged to this brood, but to none of the foregoing cage 

 numbers. This female was dissected by Mr. Hill, who found that 

 it contained only 11 ova. The largest female ever found belonged 

 also to this brood. This female was in a different series and con- 

 tained 474 ova. 



6 In this connection the writer wishes to state that two lots of females of the fall 

 brood were dissected by Mr. C. C. Hill ; Mr. P. R. Myers has determined the sex of a 

 large proportion of the flies as they emerged, and both men have helped in collecting 

 and caging the material. All of the work has been done in the laboratory at Carlisle, 

 Pa., and most of the material has been collected near by. 



