349 



after sunset was necessary for oviposition and that the niaxiniuni number 

 of eggs laid was on the second, third, and fourth days after emergence. 

 In prediction work, therefore, at least two days should be allowed for the 

 time from emergence to egg laying, as very few eggs are laid the first day. 



c. Incubation of Eggs. 



The hourly velocity values for pupal development (Table I) may be 

 used also for incubation, but the normal developmental total is 3864 in- 

 stead of 0480. Standard time for incubation, calculated on a basis of 

 384(1 developmental units (from Glenn's 1016 data), is shown in Table X, 

 together with the actual time for groups of 60 eggs for all the Olney data. 

 The method by which the theoretical time for each of these groups was 

 calculated is shown in Table IX. The ratio of actual to theoretical time 

 averaged 98.4 per cent for all eggs recorded; it would be 100 per cent if 

 3864 developmental units had been used as the normal total. Deviations 

 from standard time for all generations of all years for which data were 

 at hand, are shown in Fig. 28, p. 421. 



d. Larvae in Apples. 



Hourly velocity values for development of larvae in apples are shown 

 for various temperatures in Table V, p. 323. It is noteworthy that 

 lower temperatures are more effective on larvae in apples than on pupae 

 or eggs. The normal total for the period in the apple is 15,600 develop- 

 mental units, but an empirical number, 18,000, may be used to cover the 

 entire development of the larvae (except when hibernating) from the 

 time it enters the apple until it pupates, the normal total for the period 

 in the cocoon thus being taken to be 2,400 developmental units. The 

 calculated and actual time for these two parts of the larval period is 

 shown, for means of groups of 10 individuals, covering all of the Olney 

 data (1915-1917), in Table XI and in Fig. 2S. The larval period is much 

 more variable than the other stages. The ratio of actual to calculated 

 time for larvae in apples, when averaged by generations for those three 

 years, ranged from 90,5 to 108.0 per cent, with a mean of 98. T per cent. 

 The second generation of 1916 and the first generation of 191 T fell below 

 the standard time, while all generations of 1915 and the first generation 

 of 1916 were above the standard. On the other hand, the ratio of actual 

 to calculated time in the cocoon, ranging from 95.7 to 104.4 per cent 

 (generation means), was lowest when the ratio for larvae in apples was 

 101.6 per cent, in the second generation of 1915, and next lowest when 

 the ratio for larvae in apples was 108.0 per cent, in the first generation of 

 1916. That is, when the time in the apple was comparatively long, the 

 time in the cocoon was comparatively short. This is in accord with the 

 supposition that enzymes are concerned. 



In all these calculations, it was assumed that the velocity values 

 derived from the larva in the apple would hold good for the pre-pupal 

 stage in the cocoon at the same temperatures and humidities. The devia- 

 tion from calculated time may be taken as evidence that these values need 

 to be modified ; it is likelv, however, that individual variation would still 



