18 



BULLETIN 137, U. S. DEPARTMENT OF AGRICULTURE. 



hatched about November 10, 1915, and when partly grown were 

 placed in granulated smoking tobacco and kept in a cool room 

 did not transform until April, 1916. The material was protected 

 from severe freezing, but only a small proportion of the larvae sur- 

 vived the winter. The most favorable conditions for the rapid 

 development of larva? are created by (1) suitable food substances in 

 compact or concentrated form, (2) high and uniform temperature, 

 (3) high humidity, (4) protection from strong light, and (5) protec- 

 tion from rapid evaporation. At Richmond, Va., during the period 

 between August 1 and November 19. 1914, the shortest larval period 

 observed in six lots of about 20 larva? each was 39 days, and the 

 longest period was 61 days. Pressed chewing tobacco was used as 

 food. The maximum temperature during the period was 91° F. 

 and the minimum temperature was 51° F. At Key West, Fla., 

 during the period between April 16 and June 24, 1912, in cigars 

 kept at room temperature, the shortest larval period observed was 

 42 days and the longest period 66 days. The temperature of the 

 room varied from 80° to 94° F. 



Numerous experiments have shown that with concentrated foods 

 the larval period is shortened somewhat. In several experiments 

 with different foods kept under the same conditions in an automati- 

 cally regulated incubator at a constant temperature of 86° F. the 

 larval periods were as follows: In tobacco seed, 2 experiments, 29 

 and 30 days; in pressed yeast cake, 2 experiments, 27 and 30 days; 

 in pressed plug chewing tobacco, 29 days; in sliced plug smoking 

 tobacco, 30 days ; in loose granulated tobacco, 2 experiments, 35 and 

 38 days; in cigars, 2 experiments, 34 and 36 days; in cigarettes, 

 42 days. 



At Clarksville. Tenn., the following records for the larva stage 

 were obtained at room temperatures during summer : 



Table II. — Length of larva stage of the tobacco beetle (Lasioderma serricorne), 



Clarksville, Tenn., 19l.' { . 



Record No. 



Egg 

 hatched — 



Larva 

 formed 

 cell— 



Larva 

 pupated— 



Pays as 

 lafva. 



Food. 



1 



June 7. . 

 .do 



Julv 1R 



Aug. 5 



Aug. 7 



Aug. 11... 

 July 16. . . . 

 July 30. ... 

 No record . 



July 22. . 

 Aug. 17 . 

 Aug. 11 . 

 Aug. 16 . 

 Aug. 20 . 

 Aug. 2. . 

 July 25. . 



45 

 71 

 65 



70 

 31 



:is 



Pressed plug tobacco. 

 Do. 



2 



3 



...do 



Do. 



1 



. .do 



Do. 



5 



June 19.. 

 June 25.. 

 June 30.. 





6 



Do. 



7 



Do. 







THE PUPAL CELLS. 



After the larva has become fully grown and is ready to transform 

 into the pupa stage it forms, in any convenient place, the cell or 

 cocoon in which transformation takes place. Apparently no special 



