RATE OF MULTIPLICATION OF HESSIAN FLY. 5 



SPRING GENERATION. 



For the spring generation the ova have been counted for 160 

 females. The most surprising thing about the results obtained, as 

 shown in Table 2, is the general average number of ova per female 

 of 232.9. This is an average of 54 eggs per female less than was 

 found in the case of the fall brood. 



Table 2. — Average number of ova for females of the spring generation of the 

 Hessian fly ; counts made at Carlisle, Pa., in the fall of 1919. 



Cage No.- 



1841 



1842 



1869 



1875 



1876 



1880 



1881 



1882 



1883 



1891 



Totals 



Number 

 of females 

 counted. 



160 



Total 

 number 

 of ova. 



14, 591 

 6,990 



780 

 3,105 



836 

 1,356 

 1,048 



483 

 5,965 

 2,106 



37, 260 



Minimum 



per 



female. 



79 

 113 



34 

 188 



71 

 102 

 100 

 194 

 116 

 108 



34 



Maximum 



per 



female. 



386 

 372 

 297 

 350 

 255 

 214 

 227 

 289 

 370 

 309 



386 



Range. 



307 

 259 

 263 

 162 

 184 

 112 

 127 

 95 

 254 

 201 



352 



Average 



per 

 female. 



256.0 

 241.0 

 195.0 

 238.8 

 167.2 

 169.5 

 174.7 

 241. 5 

 229.4 

 210.6 



232.9 



While this work has been carried through only one spring genera- 

 tion, it is nevertheless quite evident that this generation is con- 

 stantly lower than the fall generation in its capacity for egg produc- 

 tion. The actual minimum number of ova per female is 34, which 

 is one more than for the fall brood. The maximum, 386, on the 

 contrary, is much lower, and the range of variation is only 352. 



SUMMER GENERATION. 



While data for the flies developing in volunteer wheat are scant, 

 the results obtained seem interesting enough to be included as 

 Table 3. Only 15 cases are available. In spite of the low average 

 number of eggs, this brood in all probability resembles rather closely 

 the fall generation in the number of eggs it can lay. If this should 

 prove true, it might be that the stage of growth of the plant has an 

 important relation to the size of the flies developing in a plant, 

 and consequently to the number of ova developing. 



Table 3. — Average number of ova for females of the generation, of the Hessian 

 fly developing in volunteer wheat ; counts made at Carlisle, Pa., in the sum- 

 mer of 1919. 



Cage No. 



Number 

 of females 

 counted. 



Total 

 number 

 of ova. 



Minimum 



per 



female. 



Maximum 



per 



female. 



Range. 



Average 



per 

 female. 



1990 



2 

 13 



524 

 3,027 



177 

 54 



347 



448 



170 

 394 



262.0 



2090 



232.8 







Totals 



15 



3,551 



54 



448 



394 



236.7 







