CONTROLLING CIGARETTE BEETLE IN STORED TOBACCO 3 



Arlington Experiment Farm, Arlington, Va. Here a number of 

 rooms were available which could be held at fairly constant tem- 

 peratures between 10° and 40° F. Tests were planned to be made 

 at 5° intervals throughout this range with an extra series run at 32°. 

 Petri dishes were chosen as suitable containers for the insect ma- 

 terial during exposure. The numbers of insects desired were counted 

 out as described above and placed in a sufficient number of dishes 

 that there would be no crowding. The dishes were then labeled for 

 the periods of exposure and temperatures and placed in the cold 

 rooms. Shortly thereafter the lids were removed from the dishes to 

 allow for more rapid cooling. When the exposure time had expired, 

 the dishes were removed and placed in a room with a constant tem- 

 perature of 70° F., and a humidity of approximately 70 percent. 

 Adults and larvae were examined and their mortality recorded after 

 2 and 5 days, pupae after 6 and 10 days, and eggs after 20 and 30 

 days. At first many of the tests were held for periods up to 3 

 months to check against any possible late recovery. No revival was 

 ever noted, however, and as a matter of fact the tendency was toward 

 an increased mortality among some of the weakened individuals. 



THE RESULTS 



A total of 19,595 eggs were exposed at 8 different temperatures 

 between 10° and 40° F. These had been laid on short tobacco stems, 

 as previously stated, and exposed in Petri dishes, from 200 to 400 eggs 

 being used in each test. Complete mortality was obtained by a 1-hour 

 exposure at 10° and a 3-hour exposure at 15°. At 20° and above 

 the exposure time for eggs was measured in days, as shown in fig- 

 ure 1. This diagram shows the exposures required for absolute mor- 

 tality at various temperatures, but it is possible to kill about 95 

 percent of the eggs with half the exposure necessary for a 100-percent 

 mortality. Thus there is a possibility of obtaining a measure of 

 economic control of the beetle in open warehouses where low winter 

 temperatures prevail. 



The tests on the larvae were made prior to those on the other stages 

 and no facilities at a temperature of 10° F. were available at that 

 time. One hundred full-grown larvae were placed in each Petri 

 dish, and several dishes were used for each test. Figure 1 shows the 

 results obtained on exposing 6,850 larvae. Sixty hours was required 

 to obtain a complete kill at 15° as compared with 3 hours for the egg 

 stage. At 20° the exposure for larvae was five times as long as for 

 eggs, but at 25° the exposure was the same. In each graph the ex- 

 posure period for 32° was the same as that for 30°, but above and 

 below these points the period of exposure changes rapidly. 



A total of 3,520 pupae were used in this series of tests. These were 

 counted out some 50 to 75 to a dish and exposed without opening 

 the thin pupal cells. From 6 to 10 days after exposure the cells 

 were broken open and a check made of the number of pupae and 

 their condition. Cells containing adults and larvae were discarded. 

 It is evident from the graph that pupae were about as resistant as 

 eggs to the lower temperatures, but above 25° F. they were slightly 

 more resistant, and no complete kill was obtained above 36° although 

 a 50-day exposure at 40° was tried. Pupae were killed in 1 hour 

 at 10°, in 3 hours at 15°, and in 16 days at 36°. As in the case of 



