BUREAU OF ENTOMOLOGY AND PLAXT QUARANTINE 63 
at the higher dosages. Near the median Lethal dosage, however, there 
were no significant differences between the performance of these two 
diluents. The addition of 2.0 percent of peanut oil, 1.0 percent of 
sodium oleyl sulfate, and 0.5' percent of water to cube in a dust mix- 
ture with talc as a diluent did not increase the toxicity of the mate- 
rial as compared with a cube-talc dust mixture not containing these 
conditioners. A dtist mixture containing 0.005 percent of sulfur 
nitride was nontoxic to the weevils. The addition of 0.225 percent 
of total pyrethrins to the cube-dust mixture with talc as a diluent, 
containing 0.5 percent of rotenone, markedly increased the toxicity of 
the resulting dust mixture to the pea weevil. During the course of 
these experiments it was determined that the weevils which recover 
from the paralysis induced by sublethal dosages of rotenone were 
capable of oviposition. but whether these eggs were viable was not 
learned. It was also disclosed that the weevils which developed dur- 
ing the summer were much more resistant to dusts containing rote- 
none than those that had been kept in storage from fall until the 
following spring. 
As a corollary to these insecticide tests, additional data were ac- 
cumulated which indicate that the toxic effect of dust mixtures con- 
taining rotenone to the pea weevil is attributable principally to the 
contact properties of the active ingredients, but also to the action of 
these ingredients as a stomach poison. 
Hibernation studies following the mild winter of 1937-38 dis- 
closed that pea weevils were able to overwinter successfully in grass, 
grain, weeds, weeds and straw, grain and weeds, pea-harvest debris, 
wheat stubble, duff from deciduous bushes, and debris from pine trees. 
This newly discovered information explains the presence of the 
weevils in areas remote from the preferred hibernation quarters in 
dense growths of pine and indicates the possibility of devising 
methods for destroying part of the pea weevil population during its 
overwintering period. 
Studies conducted in Oregon on the flight habits of the pea weevil 
with the aid of a rotary mechanical trap revealed that the magni- 
tude of weevil flight is governed by three major factors — tempera- 
ture, time of day. and season of the year. It was disclosed that the 
peak of flight activity occurred only when the temperatures reached 
68° to 74° F. or higher and that these flights reached their daily 
peak late in the morning and early in the afternoon. The flight of 
the weevils is practically stopped when the daily maximum tempera- 
ture fails to rise higher than 66° to 74°. In general the magnitude 
of daily flights was found to be correlated directly with daily max- 
imum temperature. It required a higher range of temperature to 
stimulate the weevils to flight during the spring and summer than 
during the fall. 
Although it has been shown definitely that the application of in- 
secticides containing rotenone comprised a very effective control for 
the pea weevil, the annual summation of the data collected on infesta- 
tions by this insect in the Palouse area of Washington and Idaho 
as obtained from the records of the pea-grading service of the Bu- 
reau of Agricultural Economics, cooperating with the Department of 
Agronomy of the University of Idaho, disclosed that on an average 
during 1938 approximately 12.5 percent of the dry peas examined 
