411 



50° F. during October (and November and December if desired) and 

 then put under proper conditions, will pupate in the latter part of Novem- 

 ber, in December, or during January or February. January 1st is about 

 a mean date for pupation outdoors, but the variation is so great as to 

 leave no scientific basis for a starting point in calculations at the present 

 stage of knowledge. January 1st was used by Glenn as a starting point 

 for summing larval temperatures. The time to pupation at 85° (or any 

 other suitable temperature) after dormancy is broken, apparently varies 

 with the length of the dormant period at all temperatures above freezing, 

 if not lower. Townsend demonstrated that changes took place at 33^ F. 

 The 1918 experimental series was largely useless for this purpose because 

 they were stored at higher temperatures. The temperatures should be 

 near freezing in the case of larvae designed for determining the time to 

 pupation after dormancy is broken. The liH!) larvae (Cases a and b 

 described on p. 410) were important in this connection because they 

 were kept at approximately 32" F. for several months and then put into 

 conditions for progress in the latter part of January. These fell into 

 three groups, the first pupating with about 285 accumulated degrees, the 

 second with about 535 accumulated degrees, and the third with about 716 

 accumulated degrees, — each reckoned above 50° F, as the starting point. 

 ( These are uncorrected sums of temperatures obtained by the method 

 which this paper aims to supplant for all purposes except rough estima- 

 tion.) All hibernated larvae on which data are available fall generally 

 into these three groups, the last being most variable. (Cf. Fig. 25 and 

 Glenn's Charts 1, 2, and 3, showing a small early group, a large middle 

 group, and a final prolonged group of pupations.) All the experiments 

 used in the calculation of relative velocities were constant-temperature 

 ones, and the sum of temperatures above fifty is much more significant 

 for them than for variable conditions. On this basis, a provisional set of 

 velocity curves were constructed (Fig. 26), and a provisional larval- 

 velocity chart was drafted (Fig. 27). Glenn's data beginning January 1, 

 li)16, were worked over, using all temperatures above 43° F., though only 

 those above 44° (the temperature suggested by the experimental data) 

 were considered as affecting development. 



The 1918 series included many larvae that pupated. These had been 

 stored at 48° F. or lower, on the assumption that the "threshold" was 

 50° F. There was, however, some variation in temperature, with the 

 result that when the last experiments were started the larvae were nearly 

 ready to pupate.* Baumberger and Townsend also found that this was a 

 very detrimental temperature. The three groups (early, middle, and de- 

 layed) were strikingly shown in nearly all cases, but they seemed unduly 

 crowded together in later cases, suggesting that prolonged mild tempera- 

 tures tend to reduce the differences between the groups. The earlier and 

 larger groups were used for estimating velocities. This was done by 

 dividing the time into the average sum of temperatures above 50° F. for 



• For this reason the tables of 1918 data are not given here. The other tables, 

 which are given, do not show the three-group pupation. 



