BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 81 
Three colonies out of 26 given opportunity in an isolated locality 
to rob honey contaminated with American foulbrood failed to contract 
the disease, although the others became infected, in tests on the relation 
of robbing to spread of the disease carried on by the Wyoming Agri- 
cultural Experiment Station. The queens from the three colonies 
were sent to Texas for breeding purposes. 
A new sublaboratory was established on February 1 at Hope, Ark., 
in cooperation with the Arkansas Agricultural Experiment Station. 
The long season in southern Arkansas will be used to advantage in sup- 
plementing the work on disease resistance. In addition, the program 
for the laboratory includes maintaining a reservoir of resistant strains 
and rearing queen bees for testing elsewhere by the Bureau and its 
cooperating agencies. 
That house -cleaning activities of the worker bees play an important 
part in disease resistance is demonstrated by the large amount of 
healthy brood reared in cells from which the bees have cleaned out 
diseased remains. Where reinfection occurs in such cases, infected 
food rather than remaining diseased material appears to be the cause. 
The fact that brood from resistant queens showed no less disease than 
that from nonresistant queens when placed in heavily diseased colonies 
further points to the importance of the house-cleaning behavior of 
bees. 
The time required for the removal of diseased brood ranges from 1.2 
to 10.9 days. The degree of resistance, however, is not entirely cor- 
related with the rapidity of cleaning out the disease. Cells found 
diseased on one inspection are not likely to be found later if inspec- 
tions are spaced several days apart. Light infections are thus apt 
to be overlooked if inspections are made infrequently. 
The effect of 8-hydroxyquinoline sulfate at a dilution of 1 to l,000 r 
added to diluted honey containing spores of Bacillus larvae and 
heated, indicates that small amounts of this substance, insufficient 
to be toxic to adult bees, greatly diminish the amount of heating 
necessary to kill the spores. The possibility of the use of this chemi- 
cal to make such honey safe to feed to bees is thus indicated if it can 
be obtained cheaply enough. 
Inoculations of colonies with spores of Bacillus larvae heated in 
diluted honey for periods of 30 minutes to 5 hours did not produce 
American foulbrood within 2 years, although spores from the same 
heated batches grew in culture after 3 to 30 days, showing that while 
the heated spores did not cause disease in a colonv neither were they 
killed. 
A positive nitrite-nitrogen test on a medium containing carrot ex- 
tract but without added nitrite has long been considered specific 
for Baeill'i.s larvae. Two other spore-bearing bacteria have been 
found, however, and isolated in pure culture but not identified, which 
give a nitrite-nitrogen test indistinguishable from that of B. larvae. 
The relationship of particle size to the toxicity of insecticides to 
honeybees has been tested for lead arsenate, calcium arsenate, phe- 
nothiazine, and cryolite. The median lethal dose for fine cryolite 
(midsize, 2 microns) was found to be 7.5 micrograms per bee; and 
for medium cryolite (midsize, 28 microns), 23.2 micrograms. The in- 
fluence of particle size was of about the same order of magnitude for 
phenothiazine as for cryolite: for lead arsenate it was much greater, 
18S500— 40 
