88 ANNUAL REPORTS OF DEPARTMENT OF Li I KM H "I .TUMB, 194 
done during a considerable portion of the time during previous years, 
and it was therefore necessary to transport laborers from Tucson to 
the mountains and back cadi day. involving between 00 and 70 
miles of travel. During the year approximately 78.480 acres were 
covered and 290,777 T hurberia plants were destroyed. It is esti- 
mated that at least M."> percent of the T hurberia plant- destroyed car- 
ried or showed damage by the Thurberia weevil. Since the inaugu- 
ration of this project in VXWk a total of :J7<>,(».">0 a<res have hern 
covered and 2.05.V>39 Thurberia plants have been destroyed. 
This project was brought to a close on June 15, 19-10, because work 
had been completed on the area to be cleaned under tin' original 
program, and sufficient funds were not forthcoming to inaugurate a 
more comprehensive program. Funds to carry on this work have 
been provided by YV. P. A. allotments, supplemented by funds allo- 
cated by this Bureau. 
BEE CULTURE 
POLLEN STUDIES 
A correlation of the annual brood-rearing cycle of a colony of honey- 
bees with pollen income has shown that the peak of egg laying occurs 
during the peak of pollen income. The spring peak of colony popu- 
lation was found to occur 5 weeks after the maximum pollen income. 
An ample supply of pollen during the 5-week period prior to the honey 
flow is therefore essential to maximum colony strength for honey 
production. 
Experimental colonies equipped with pollen traps gathered 1 pound 
or more of pollen per day on several occasions during fruit bloom. 
The largest daily yield was 1 pound and 11 ounces, estimated to be 
equivalent to the loads of 128,GG5 bees. One colony produced 42.7 
pounds of pollen during the active season, an amount that would re- 
quire the labor of 1,767,665 bees making single trips. Since 1 bee 
visits from 80 to several hundred blossoms to obtain a load of pollen, 
the pollination service of a colon} 7 is enormous. 
The pollen content of fresh nectar from 38 species of plants ranged 
from zero in 1 navel orange to 176.000 grains per cubic centimeter in 
A ///.w'///'ZvV/.. In nectar from deciduous fruits the pollen content ranged 
from 1,800 grains per cubic centimeter for peach to 11,000 grain- ror 
apple. The nectar of other important honey plants contained the 
following amounts: Black locust, 2,800; sages, 4.000 to 5,000: dande- 
lion. 12,800; mustard. 81,000; Dutch clover, 42,400; and nianzanita, 
()9.0()U grains per cubic centimeter. The feeding of sirup containing 
no pollen to colonies Inning ample pollen reserves did not stimulate 
egg laying whereas after the addition of pollen to the sirup expansion 
in egg laving was noted within 24 hours. The pollen Suspended in 
nectar and honey unquestionably influences brood rearing, for normal 
brood rearing requires both pure pollen and pollen suspended in the 
liquid food. 
Bees show remarkable ability to remove suspended pollen contained 
in their honey stomachs. After 15 minutes' retention in the honey 
stomach a sirup coiit aining^MW- pollen grains per cubic centimeter 
was reduced to -JD.OOO grains and practically all grains disappeared in 
an hour. / 
Soybean flour supplemented by '2f> percent of pollen stimulated brood 
production during iM'bruarv, March, and April. The overwintered 
