26 BULLETIN 737, U. S. DEPARTMENT OF AGRICULTURE. 
could be heated gradually by an alcohol lamp underneath. By this 
means the temperature of the tube containing the beetles could be 
gradually raised or lowered as desired. In experiments with descend- 
ing temperatures the beetles were taken from a lot reared in con- 
finement and were kept at a constant temperature of 81° F. Those 
used in tests of rising temperatures were kept for a short time at 
32° and were inactive when the experiment was commenced. Ten 
beetles were used in each test, a different lot being used each time. 
With increasing temperatures the beetles begin activity at tempera- 
tures between 48° and 75° F., one-half being active at 60° and 75 
per cent at 64° F. With decreasing temperatures the beetles become 
inactive between 62° and 48° F., one-half being inactive at 56° and 
75 per cent inactive at 55° F. In infested tobacco warehouses the © 
adults are seldom found active at temperatures below 65° F. 
Activity increases as the temperature becomes higher. At tempera- 
tures between 117° and 120° F. all activity ceases, and temperatures 
above 117° F., if continued, result in death. 
SEASONAL HISTORY. 
SEASONAL ABUNDANCE AND NUMBER OF GENERATIONS. 
Since the tobacco beetle is an indoor or stored-product insect, the 
terms “brood” and “generation” can hardly be appled in the 
sense that they are used in dealing with field insects, as the seasonal 
appearance and number of generations of such insects depend largely 
upon the variations in climatic conditions. In food substances main- 
tained at constant warm temperatures adults may be found at any 
season of the year, and the wide variations in the time required for 
development under the same breeding conditions produce an over- 
lapping of generations. Under ordinary conditions in warehouses 
there are, however, well-marked periods during which the adults 
are most abundant. At Key West and Tampa, Fla., most cigar man- 
ufacturers state that the adults are most abundant, during the 
months of February and March, and again in August and Septem- 
ber. At these places, however, the abundance of adults at any time — 
may depend more upon the time the heaviest shipments of cigar 
tobacco from Cuba are received than upon local climatic conditions. 
In the latitudes of Virginia and Tennessee there seems to be a ~ 
period of greater abundance with the advent of the first warm ~ 
weather in June, and again a marked increase occurs during Sep- 
tember. 
In tobacco warehouses at Clarksville, Tenn., adults usually begin 
to appear about May 1, and after November 1 comparatively few 
adults can be found. In unheated buildings three generations are 
possible between May 1 and November 1. 
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