56 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
The conclusions presented herewith are drawn from the data pre- 
sented in Table VIII, based upon daily observations of over 5,000 
eges deposited at intervals from February to October. From these 
and other data not included, it can be stated that the eggs hatch dur- 
ing a period of from 8 to 24 days after deposition, according to the 
season of the year. While there are no data regarding the length of 
the incubation period for eggs deposited by the few female flies occa- 
sionally seen during the winter months, as noted under seasonal his- 
tory, it is probable. that hatching extends over even a greater number 
of days during the winter season. The deposition of such eggs is, 
however, a comparatively rare occurrence and will receive no further 
mention here. In no instance have eggs been seen to hatch before 
the eighth day from deposition, even during the months July and 
August, 1907, when the average mean temperatures were slightly 
above normal, while under the most favorable summer weather con- 
ditions from 75 to 100 per cent of the eggs hatch during the period 
from the tenth day to the twelfth day from deposition. 
In general, the warmer the season the shorter and more nearly uni- 
form is the period of egg development or incubation. During the 
months of July and August, when the normal monthly temperatures 
at Orlando range from about 72° F. as the mean of the minimums to 
about 93° F. as the mean of the maximum records, practically all the 
egos hatch from the tenth day to the twelfth day. Even at this most 
favorable season, in one instance hatching was delayed for 19 days. 
During the somewhat cooler weather of late September and early 
October and the decidedly cooler months of February, March, and 
April, hatching is more or less delayed according to the prevailing 
temperature and is scattered over a larger number of days. This 
same result is brought about, only in a less degree, by a cool period 
occurring in an otherwise warm season, as shown under record 4 
(Table VIII). 
Reference to the daily rate of hatching in Table VIII, and to the 
accompanying degrees of accumulated effective temperatures, shows 
that regardless of the time of year deposited and the number of days 
required for incubation, over 90 per cent of the eggs, on an average, 
hatch between the accumulation of from 375° to 475° of effective 
temperature. 
Exception to this statement must be taken in records 1 and 2 
(Table VIII). The number of degrees of effective temperature 
required seems to be greater at this season, although this might not 
prove to be the case if, as is probable, an error has arisen from using 
43° I’. as the basis for calculating the effective temperature. 
Reference to the two preceding tables shows that considerable 
variation exists in the length of the egg stage among eggs deposited 
on the same day, or even within the same hour, and subsequently 
