BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 
89 
bees were replaced by young bees to such an extent that approximately 
3y 2 pounds of young bees could have been removed for packages dur- 
ing the last week in April. 
NECTAR-SECRETION STUDIES 
Light, atmospheric pressure, and temperature influenced nectar 
secretion in greenhouse poinsettias. The sugar content of the nectar 
varied inversely with the relative humidity but directly with the 
amount of air movement, when the temperature remained constant. 
Tests indicate that the shape of blossoms, in addition to weather fac- 
tors and differences in species of plants, may also contribute to differ- 
ences in nectar concentration. In a saturated atmosphere sirups con- 
taining more than 38 percent of invert sugar tended to become more 
dilute, while those of lower sugar concentration tended to become more 
concentrated. 
Laboratoiy studies on nectar secretion in alfalfa indicate that length 
of exposure to light influences the time of blossoming. The average 
raceme contains 16 blossoms, those at the distal end blooming about 
4 days later than those at the base. The blossoms wither in about 
7 days. The mature blossoms have richer nectar than the immature. 
The alfalfa blossoms yielded from 0.82 to 2.4 microliters of nectar, 
and from 15 to 45 blossoms were required to furnish 1 bee load. In 
contrast, orange blossoms yielded BO to 40 microliters of nectar, and 1 
to iy 2 blossoms yielded a bee load. The nectar in the unopened orange 
buds contained 16 percent of sugar and that in open blossoms from 16 
to 50 percent. 
INVESTIGATIONS AND AMERICAN FOULBROOD 
In the cooperative studies on the resistance of honeybees to American 
foulbrood, of 317 queens of resistant stock 78 percent either recov- 
ered or failed to contract the disease. In Iowa 347 queens were tested 
by beekeepers under conditions of infection normally existing in non- 
isolated communities. 
Seventy-eight queens of strains having no history of resistance were 
tested at Hope, Ark. Since difficulty was experienced in obtaining 
infection in the few colonies developing disease, comparative tests 
with strains similar to those under test in Iowa and Wyoming have 
been begun to determine whether the climate or the honey flow influ- 
ences the results. 
The behavior of bees toward diseased remains indicates that resist- 
ance to American foulbrood is concerned with bee behavior and is 
not physiological in its nature. Primary infection takes place in 
3'oung larvae 2 days or less after hatching! the infectious period coin- 
ciding with the initial feeding stage rather than with the later feed- 
ing stages, as had been supposed previously. This conclusion has 
been further substantiated by the inoculation of individual larvae. 
It has also been demonstrated that only relatively few spores per larva 
are required to produce infection, a matter of great importance to 
an understanding of the development and spread of this disease. 
Spores of Bacillus larvae, the causative organism of American 
foulbrood, subjected to sublethal heating were found to be more 
exacting in their nutritive requirements in culture than wore un- 
treated spores. Unheated egg-yolk medium containing extract of dry 
yeast, carrot extract neopeptone, and dextrose gave excellent results. 
Spores boiled in water for 7 hours as well as those autoclaved at 
