CONTROLLING CIGARETTE BEETLE IN STORED TOBACCO 5 



posure at 36° than at 30° or 32° is required to produce complete mor- 

 tality. The positions of the points for the adult insect at 30°, 32°, 

 and 36° are in contrast to those for the other stages, though it requires 

 17 days longer to effect complete mortality at 40° than at 36°. It 

 seems evident from these results that death is produced, not from 

 freezing nor from the crystallization of water in the insect, but from 

 some physiological condition brought about by these low temperatures, 

 and that the same effect may be produced in approximately the same 

 time at various temperatures between 30° and 36°. 



Some work was done on the freezing of the various stages of this 

 insect, but lack of time prevented carrying this portion of the problem 

 to completion. In the work done it was found that all stages of the 

 insect were readily undercooled well below the freezing point. In 

 some cases the insect would not begin to freeze until below 0° F. 



Powell 4 reports a 57-percent mortality among eggs exposed for 20 

 days at a temperature of approximately 35° F. This is in contrast 

 to the exposure time of 11% days for complete mortality at 35° as 

 shown in figure 1. In the present work an extremely wide fluctua- 

 tion in resistance was found among individuals. The insects used 

 in making these determinations were reared on corn meal at a tem- 

 perature of 80° and a humidity of approximately 70 percent. In- 

 dividuals reared under different conditions of temperature and 

 humidity might show a difference in resistance to low temperatures. 

 Checks made at 25° with insects reared on tobacco showed no sig- 

 nificant difference in resistance between the individuals reared on 

 the two diets. It was noted, however, in the tests on the undercool- 

 ing point, that individuals reared in a relatively dry laboratory room 

 generally had a very low undercooling point. It should also be 

 pointed out that individuals recently collected from tobacco ware- 

 houses may be slightly more resistant owing to an overwintering rest 

 period denied those continuously reared in a laboratory. 



RATE OF COOLING OF BALES AND HOGSHEADS OF TOBACCO 



To make this work applicable to the control of insects under ware- 

 house conditions it was necessary to determine the rate of cooling of 

 commercial packages of unmanufactured tobacco as well as to de- 

 termine the reactions of the insect in this special habitat. A series 

 of experiments were therefore carried on to determine the length of 

 time required for various types of commercial packages of unmanu- 

 factured tobacco to cool to low temperatures in a commercial cold 

 storage. 



Four bales of cigar tobacco and one hogshead were borrowed from 

 tobacco companies at Eichmond, Va. The bale of Connecticut shade 

 wrapper was packed in a wooden crate measuring 15 by 33% by 35% 

 inches. The bale of Puerto Kican long filler was wrapped in heavy 

 paper and enclosed in a burlap case. The dimensions were 22 by 25% 

 by 32 inches. The bale of Florida shade wrapper was packed in a 

 tight pasteboard carton measuring 13 by 33 by 34% inches. The Wis- 

 consin filler was in a wooden case so open that it offered little insula- 

 tion to the bale. Its dimensions were 30 by 29 by 40 inches. The hogs- 

 head Avas 54 inches high and 48 inches in diameter and enclosed in 

 a thin slat crate. 



4 See footnote 3. 



