254 
INCUBATION PERIOD 
Eggs of the first generation hatch during May and June. The ~ 
period varied from 13 days during the cooler period early in May to 6 
days during the warmer parts of June, the average being 9 days for the 
243 eggs used in the life history series. In a larger series of observa- 
tions consisting of 2664 eggs the period varied from 15 days to 6 days 
and the average was 9.3 days. 
Eggs of the second generation hatched during July, August, and the 
early part of September and the incubation period varied from 5 to 9 
days, depending upon the temperature, the average for 106 eggs from 
which transforming larve hatched being 6 days. The eggs of the trans- 
forming larve hatch prior to the middle of August, during the warmest 
part of the season. Their incubation period is shorter than the period 
of those from which the hibernating larve hatch later in the season. The 
average period for 1748 second-generation eggs was 6.6 days. 
Eggs of the third generation hatched during the latter half of August 
and during September. The period varied from 6 to 15 days, the average 
for 302 eggs observed being 8.2 days. 
Eggs of the hibernating generation, which consists of a very small 
per cent. of the first generation, a larger per cent. of the second, and all 
of the third generation, hatched during July, August, and September. 
The incubation period varied from 5 to 15 days, the average for the 242 
eggs used in the life-history series being 6.7 days. 
There was practically no difference between the incubation period 
of male and of female eggs; the average period of 340 of the former 
belonging to all generations was 7.9 days and of 395 of the latter 7.8 days. 
Early in May and late in September the incubation period is com- 
paratively long, varying from 12 to 15 days. It decreases in length till 
midsummer, when it is only 5 days, and then increases in length till the 
end of the season. The relation of temperature to the length of the in- 
cubation period is shown in Table 1, page 235. 
LARVAL PERIOD 
Transforming larvae.—The larval period of the first generation of 
larve reared in apples on the tree varied from a maximum of 42 days in 
the fruit and 9 days in the cocoon to a minimum of 18 days in the fruit 
and 1 day in the cocoon, the average period in the fruit being for males 
27.6 days, for females 28.3 days, and for both males and females 27.9 
days, and in the cocoon 4.2 days for both males and females. 
The larval period of larve reared in picked apples averaged 21.2 
days in the fruit and 4.4 days in the cocoon. The average total larval 
period of 227 first-generation larve reared in apples on the tree was 
32.5 days and of 113 larve reared in picked fruit 25.8 days, the differ- 
ence being 6.7 days. It was shown in Tables 3 and 4 that the accumula- 
