FECUNDITY OF WINGLESS VS. WINGED FEMALES. 75 



and as the individuals were isolated and protected as much as pos- 

 sible from natural enemies it is probably safe to say that this average 

 is as high as would obtain in the open fields, where they are convenient 

 prey for their enemies. 



Mr. Urbahns found that in Texas the average number of young 

 produced in the spring and fall was much greater than in the summer. 

 The averages for December and January agree very well with those 

 of the summer period. 



The maximum number of young produced by a single individual, 

 under observation by Mr. Urbahns, that began reproducing in De- 

 cember and January was 29, the average for this period being 17. 1; 

 the maximum for those that began reproducing in April and May 

 was 84, the average being 58.5 young; the maximum for those that 

 began reproducing in June, July, and August was 39, the average 

 being 17.2 young; the maximum for those individuals that began 

 reproducing after August was 73; the average for the period from 

 March to November is 39.7; the average for the entire number of 

 individuals upon which Mr. Urbahns made observations during 1909, 

 including the rearings during December and January, *is 34 young. 

 As will be observed, this is considerably above the average for 

 Indiana. 



From the foregoing data it will be seen that the spring, in both 

 the North and the South, is the most favorable period for reproduc- 

 tion; in the North the summer period ranks next, the fall coming 

 last, while in the South the summer is so hot that the aphidids can 

 scarcely live at all, the fall ranking next to spring for productiveness. 



FECUNDITY OF WINGLESS VERSUS WINGED FEMALES. 



In 1890 the senior author gathered from his observations that the 

 wingless forms were more prolific than the winged. In 1907 the 

 junior author came to the same conclusion. In 1909 Mr. Urbahns, 

 in Texas, observed that the winged forms did not appear to be so 

 prolific as the wingless forms. During the summer of 1909, at La 

 Fayette, Ind., the junior author carried on some experiments with a 

 view of learning, if possible, something definite in regard to this 

 matter. For this purpose 8 nymphs with wing pads and 8 larvae in 

 the fourth stage were selected and each placed in a separate cage, 

 each cage being placed under the same conditions. This experiment 

 began on the 30th of August and all individuals became adult about 

 the same time. The maximum number of young produced by a 

 single winged individual was 44 and the minimum was 10; the maxi- 

 mum number of young produced by a single wingless individual was 

 61 and the minimum was 4. The total number of young produced 

 by the 8 winged individuals was 224, or an average of 28 young for 

 each individual; the total for the 8 wingless individuals was 274, or 



