BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 95 
tures of these have shown good results. Over 90-percent kill was 
demonstrated at a dilution of 1 to 6,000,000 of a 15 to 1 pyrethrum 
extract. A pyrethrum solution containing 1.0 gram of total pyre- 
thrins per 100 cubic centimeters in Diesel oil and carbon tetrachloride 
gave good kills in a dilution of 1 to 10,000,000, and more than a 60- 
percent kill at 1 to 30,000,000. 
Because the eggs of the gnat concentrate in huge drifts, very fre- 
quently along the shore, the use of an ovicide is promising. The New 
Jersey pyrethrum-oil emulsions destroy the eggs effectively in the 
laboratory, and a few field tests indicate that the destruction of a 
large percentage of the eggs can be accomplished with them under 
certain conditions. 
INSECT SECRETIONS 
Results of the year's investigations of insect secretions have had a 
far-reaching influence in the field of biology and medicine. These 
studies revived an interest in the enzyme urease. This enzyme, which 
is necessary to certain life processes, has been known for the last 80 
years but has been largely neglected in the field of biology. Two 
additional extracts, designated respectively as "maggot extract F" 
and "maggot extract K," were discovered. The former promises to 
be of greater value in healing various types of wounds than any of 
those already found and now widely used in medical practice, and 
there has been a great demand for it by various clinics and hospitals. 
Although maggot extract K has as its special use the treatment of 
the bone infection osteomyelitis, it is also suitable for other nonheal- 
ing wounds. 
In the study of insect secretions it is necessary to determine the 
presence of materials in minute insect organs. To accomplish this, 
ingenious apparatus was developed with which determination can be 
made of the presence of urease in the brain, heart, stomach, Mal- 
pighian tubules, and wing muscles of individual larvae and pupae of 
blowflies. 
TICKS AFFECTING MAN 
Extensive tests were made to determine the efficiency of controlling 
adult American dog ticks by spraying vegetation with nicotine sul- 
fate. This method was fairly successful in some cases, since a 
90-percent reduction was apparent after 48 hours. 
By marking ticks found in nature and observing their movements 
from month to month, it was shown that they concentrate along 
roadways and paths frequented by man and dogs. This emphasizes 
the need for an effective method of destroying the adults where they 
are thus concentrated. 
Studies on host relationships confirmed previous data to the effect 
that meadow mice were by far the most important hosts of the im- 
mature stages of ticks. Rabbits were shown to be minor hosts. An 
experiment to determine the effect of meadow-mouse control, begun 
2 years ago, indicated that tick infestation on the controlled area 
was reduced even though some mice came into the area. Accordingly 
it was decided to carry out, in cooperation with the Fish and Wildlife 
Service, a further test on an isolated tract where mouse control 
could be kept more complete. Owin^ to the slow development of this 
tick definite results will not be available for 2 or 3 years. 
