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BULLETIISr 1393, U. S. DEPARTMENT OF AGEICULTUBE 



THE EGG 



INCUBATION PERIOD 



Data on the incubation period of tlie granary weevil accompanied 

 by the maximum, minimum, and mean temperatures for the period, 

 have never been pubhshed. References to the length of the egg 

 stage are very fragmentary except those by Strachov-Koltcmn 

 (65), in which the day, but not the night, temperatures are given. 

 This writer concludes that the incubation period may range from 

 about 5 days at 75° F. to 15 days at 62° F. Observations made on 

 individual eggs indicated that at 75° F. the incubation period might 

 be 5 to 6 days; at 73° and 82° F., 6 days; at 69° F., 8 days; at 68° 

 F., 9 days; and at 67° F., 9 to 10 days. 



Table 4. — Duration of the egg stage of the granary weevil 



No. 



Date egg 

 laid 





1919 



1 



Sept. 30 



2 



Oct. 1 



3 



Oct. 2 



4 



Oct. 3 



5 



Oct. 15 





1920 



6 



Mar. 18 



7 



Mar. 25 



8 



Mar. 26 



9 



Mar. 28 



10 



Apr. 9 



11 



Apr. 13 



12 



Apr. 16 



13 



Apr. 20 



14 



June 23 



15 



June 26 



16 



July 3 



17 



July 14 



18 



July 15 



19 



July 20 



20 



July 24 



21 



Aug. 5 



22 



Sept. 1 



Date egg 

 hatched 



1919 

 Oct. 5 



.__do 



Oct. 6 

 Oct. 7 

 Oct. 19 



1920 

 Mar. 24 

 Mar. 31 

 Apr. 1 



Apr. 3 

 Apr. 15 

 Apr. 18 

 Apr. 21 

 Apr. 25 

 June 27 

 June 30 

 July 7 

 July 18 

 July 20 

 July 24 

 July 28 

 Aug. 9 

 Sept. 5 



Temperature 



for incubation 



period 



op 



79.8 

 78.0 

 83.1 

 83.1 

 80.4 



69.7 

 76.8 

 77.5 



78.1 

 66.6 

 68.7 

 76.1 

 78.9 

 79.9 

 78.6 

 82.9 

 81.0 

 81.3 

 81.5 

 80.5 

 80.2 

 81.6 



Length 

 of egg 

 stage 



Days 

 5 

 4 



4 

 4 

 4 



No. 



Date egg 

 laid 



1920 

 Sept. 2 

 Sept. 3 

 Oct. 5 

 Nov. 7 

 Nov. 12 



Nov. 15 

 Dec. 4 

 Dec. 15 

 Dec. 16 



1921 

 Jan. 11 

 Jan. 21 

 Jan. 23 

 Jan. 31 

 Feb. 2 

 Feb. 3 

 Feb. 11 

 July 26 

 July 30 

 Aug. 2 

 Aug. 15 

 Sept. 26 



Date egg 

 hatched 



1920 

 Sept. 6 

 Sept. 8 

 Oct. 12 

 Nov. 13 

 Nov. 17 



Nov. 20 

 Dec. 19 

 Dec. 25 

 Dec. 24 



1921 



Jan. 20 



Jan. 30 



Feb. 1 



Feb. 12 



Feb. 14 



Feb. 15 



Feb. 23 



July 30 



Aug. 3 



Aug. 6 



Aug. 20 



Oct. 1 



Temperature 



for incubation 



period 



°F. 

 81.5 

 82.8 

 70.9 

 72.1 

 68.5 



62.9 

 61.0 

 60.0 

 61.2 



61.2 

 62.6 

 64.0 

 67.6 

 66.2 

 66.5 

 65.2 

 85.4 

 81.5 

 83.5 

 76.5 

 72.5 



Length 

 of egg 



Days 



Of the data presented by the writers in Table 4, those for 1919 

 and 1920 were secured under the semi tropical conditions of Florida 

 and those of 1921 under laboratory conditions at Washington, D. C. 

 These data indicate that the minimum period for egg development 

 is 4 days when the temperature means average about 78° to 80° F. 

 The longest incubation period, 15 days, recorded in Table 4, covers 

 a period when the daily temperatures ranged from a minimum of 

 35° F. to a maximum of 84° F., with a mean of 61° F. But at a 

 mean of 60° F., with the same range in the maximum and minimum 

 temperatures for the period, one egg (No. 30) required only 10 days 

 for development. Certain eggs held for 28 days in refrigeration at 



