THE CITRUS WHITE FLY: LIFE HISTORY AND HABITS. 69 
depositing eggs or. new growth in a very sheltered place. The average 
mean temperature of the 6 days preceding this observation was 66° 
F., while, for the 6 days preceding these, when no white flies were 
on wing, the average mean was about 58.5° F. Adult white flies 
were not seen in the laboratory grove in February, 1909, until about 
the 20th, or until the temperature records for the grove showed an 
average daily mean of about 64.5°. It is from the above facts that 
the lowest temperature at which emergence occurs has been deter- 
mined to be about 62° F. This conclusion, drawn from general field 
observations, is strengthened by emergence records kept in con- 
nection with cage life-history work during the period of active spring 
emergence of March, 1908, when the monthly mean was 71°. Refer- 
ence to the data contained in Table XI brings out the fact that while 
TaBLE XI.—Relation of temperature to emergence®of the citrus white fly. 










| 
‘ Emergence records. 
|Rangein| Average 
Date. | tempera- | mean tem- 
nue. persue Norse No. 2. No. 3. | No. 4. 
EOS Se el) Mere Ba | 
Mar. 19 62-89 (O40 Asie lesa =n 6 2 
Mar. 20 63-90 76. 5 5 18 78 4 
Mar. 21 54-65 59.5 0 0 i iL 
Mar. 22 60-80 70. 0 10 15 69 15 
Mar. 23 66-90 | 78. 0 ily 35 71 4 
| 

emergence had been going on actively two days before and after March 
21, when the average mean temperature was about 75° F., a drop in 
the mean temperature on the 21st to 59.5° F. practically prevented 
any white flies from emerging. The 1 white fly that is recorded 
under Nos. 3 and 4 may have emerged on the 20th after the daily 
record had been taken. Such emergences are not rare at this season 
of the year, as will be shown later. Of 2 lots of about 100 pup 
each, from which adults were nearly ready to emerge, 1 was placed 
in a refrigerator at about 56° F, and the other kept at room tempera- 
ture which ranged between 70° F. and 80° F. while emergence was 
taking place. Of those kept on ice, but 1 white fly emerged 
during the first 12 hours, as compared with 17 from pup kept 
at room temperature. White flies continued to emerge on 3 
consecutive days from pup kept at the latter temperature. No more 
emerged from the refrigerated pupw. It is therefore evident that 
emergence may. occur at as low a temperature as 56° F., though very 
rarely. 
That white flies seldom emerge after the temperature reaches 85° 
F. may be concluded from the following facts: During the months of 
July and August, when the average daily mean is about 82° F., a 
newly emerged adult is rarely seen in the grove after 8 a.m. Prac- 
