ENTOMOLOGY AND PLANT QUARANTINE 
of sugar sirup. To facilitate the preiniration of this solution, a method has 
been devised for preparing in powdered form measurable quantities of approxi- 
mately known numbers of spores of Bdcillus larvae. Cultural studies of various 
strains of the organism have shown wide variation in huigth of the incubatiou 
period and in the greatest dilution that will give growth in cHlture. 
Losses of queens shipped under present standards are too high, particularly 
during hot weather. Provision for a continuous water supply has given promise 
of reducing such losses, while for queens caged for long periods, pollen added 
to the queen-cage candy in addition to a water supply has been shown to be 
beneficial iu preliminary tests. 
It has been found that relative humidity has a more marked effect on the 
longevity of caged bees than any other environmental factor. Relative humidi- 
ties of about 20 to 2") percent, together with ."iO-percent sucrose solutions in 
water and with additional water available, provide satisfactory conditions for 
caged bee studies. The most suitable temperature conditions have not been 
determined, but the length of life at temperatures of 84° to 93° F. is sutti- 
ciently long for most comparative testing. 
Studies on the lethal effect on bees of arsenicals used as in.stnjticides show 
that a dose containing only 0.05 to 0.10 microgram of elemental pentavalent 
ar.senic is sutHcient to cause a significant shortening of life. The w^ork also 
indicates that calcium arsenate (Ca;;( AsOi)2) is somewhat more toxic to bees 
than acid lead arsenate (PbHAs04). 
Preliminary crosses and backcrosses of the Italian and Carniolan races by 
the Watson method of artificial insemination gave no indication of the com- 
plete dominance of either yellow or black as far as coloration of abdomens 
and scutella of the worker progeny is concerned. 
^^'hat has been tentatively designated as a haplo-diploid mosaic drone was 
discovered in the experimental apiary at Beltsville. Md. It bears dark hairs 
on one side of its thorax and yellow hairs on the other, and shows some 
difference of coloration in the two sides of the anterior abdominal tergites. 
Studies on two different connnercial strains of the Italian bee reared in this 
country showed one to be approximately twice as good as the other in lioney- 
storing ability, and also to be definitely superior in amount of brood reared and 
in drawing out foundation. 
Spores of BoeiUux larvae failed to grow in culture after they were boiled 
in water for H hours and also after they were autoclaved at 15 i)ouuds' pressure 
for 30 minutes. With all shorter periods of heating, growth was obtained in 
some of the cultures. Three hours of exposure to flowing steam failed x^^ 
destroy all the spores. In concentrations ranging from 1 pound in .5 gallons to 
1 pound in 30 gallons of water, both potassium hydroxide and sodium hydroxide 
failed to destroy spores of B. larvae within 3 days. 
European foulbrood did not recur in colonies of Caucasian or Carniolan bees 
but did recur in all experimental colonies of common black bees. 
IN\^ESTIGATIONS OF INSECTS AFFECTING MAN AND ANIMALS 
SCREWWORMS AND OTHER BLOWFLIES 
Further research on the biology and habits of scrcwworms and other blow- 
flies has developed promising methods of determining the influence of climato- 
logical and other ecological factors which favor the development of, and are 
responsible for, local outbreaks and the natural dissemination of these pests. 
In the overwintering area in Texas, during 1937, foci in which factors 
appeared favorable for the rapid building up of screwworm fly abundance 
were located at certain points along the Rio Grande and in the lower Rio Grande 
Valley. By following the natural migration of the fly from the overwintering 
area and studying the rate at which the flies increased after reaching given 
localities, it was determined that all of Texas, parts of western Louis- 
iana, and the lower desert section of Arizona were reinfested early in July. 
In 1937 the rate of migration was about the same northward as in 193() but was 
more rapid toward the east. After spreading over the Gulf Coastal Plain in 
Texas the screwworm population reached its peak early in ^hxy. Along the 
escarpment of the P:dwards Plateau the build-up of the fiy population was at a 
more rapid rate and did not reach its peak until early in June. On the Edwards 
Plateau the flies were continuing to increase at the end of JiUy. ^^'ith the 
24695—37 5 
