BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 85 
CONTROL INVESTIGATIONS 
CONTROL OF INSECTS BY FUMIGATION 
Iii cooperation with certain shippers tests were made on the possibility of 
fumigating beans in box cars for the bean w r eevil (Acanthoscelides ohtectus 
Say) and the southern cowpea weevil (Callosobruchus maculatus F.). In this 
work infested beans were placed in sacks of beans in cars and fumigated with 
hydrocyanic acid for a period of 24 hours with dosages ranging from 4 to 14 
pounds per car. Each carload consisted of approximately 60,000 pounds of 
beans. From the results of this work, which was done at North Kansas City, 
Mo., and in which eight carloads of beans were fumigated, it seems probable 
that, at temperatures above 60° F. and with a dosage of approximately 14 
pounds of hydrocyanic acid per carload, and with proper spacing of the sacks 
so that the fumigant can penetrate to all parts of the car, satisfactory kills of 
the two bean weevils could be obtained. The suggestion is made that loaded 
cars be fumigated in chambers for the purpose of eliminating wind currents, etc. 
Work was continued on atmospheric and vacuum fumigation of vetch seed 
with liquid hydrocyanic acid and carbon disulphide for the vetch weevil 
(Bruchus brachialis Fahr.). At present both fumigants appear promising. 
STERILIZATION OF PLANT PRODUCTS BY HIGH AND LOW TEMPERATURES 
The length of exposure necessary to kill eggs, larvae, pupae, and adults of 
the cigarette beetle at temperatures of 10°, 15°, 20°, 30°, 32°, 36°, and 40° F. 
and the time necessary to cool several different types of commercial packs of 
leaf tobacco to low temperatures were determined. The time of exposure to 
produce complete mortality varies with the temperature from a minimum of 
0.04 day at 10° for the eggs to 40 days at 40° for the adults. This method 
is adapted to the commercial treatment of tobacco for this insect. 
METHOD OF APPLYING INSECTICIDES 
Tests were made of high-pressure sprayers for woodland spraying for the 
gypsy moth. Specifications were written and sprayers purchased which were 
highly efficient and economical in price and upkeep. 
PHYSIOLOGY OF INSECTS 
In the studies of digestion in a leaf-eating insect, the southern army worm 
(Prodenia eridania Cram.) was used and the presence of nine enzymes was 
shown in the digestive tract of the larvae. These were found in the tissues 
of the midgut. It is of interest to note that only two enzymes were found in 
the tissues of the foregut and only two in the tissues of the reargut. The 
midgut is apparently the portion of the alimentary tract in which most of 
the digestion takes place, or at least in which most of the digestive enzymes 
are secreted. 
TOXIC EFFECT OF INSECTICIDES ON INSECTS 
In investigations carried on during the last 2 years, a wide variation in the 
toxicity of various calcium arsenates to silkworms and to bean plants has been 
shown to exist. It has been shown also that this variation is apparently 
related to the amount of water of crystallization in the compound : that is. cal- 
cium arsenates from which the water of crystallization has been driven off are 
apparently nontoxic to both silkworms and bean plants, hut where the water 
of crystallization is present the toxicity is decidedly higher. The extent of 
loss of toxicity of tricalcium and tetracalcium arsenate resulting from the 
application of heat depends on the duration and temperatures of heating and 
on moisture conditions during heating. 
Insecticidal tests of 300 alcoholic extracts of flower heads of selected pyre- 
thrum plants were made in cooperation with the Bureau of Plant Industry to 
correlate insecticidal activity of the toxic constituents with morphological char- 
acteristics of the plant. It was expected that this work would provide a means 
for selecting the most toxic plants for propagation. A method of employing 
mosquito larvae as test insects was developed and used for this work. 
