GRAIN CONSERVATION 113 



this rate under various conditions of temperature 

 and moisture. Some of our results may interest 

 you. 



A single pair of rice-weevils {Calandra oryzae), 

 isolated on April 23rd, 1918, and kept in wheat in 

 a moist incubator, at an average temperature of 

 28° C. (82*5° F.), increased in 29 days to 6 live adults, 

 in 48 days to 19, in 69 days to 113, in 97 days to 758. 

 All loose weevils were then removed and in another 

 fortnight 653 more live adults were found amongst 

 the grain. Thus in 111 days — almost exactly 16 

 weeks — a single pair of these insects had multiplied 

 about 700-fold. 



At ordinary laboratory temperatures, with the 

 room only slightly heated in cold weather during 

 the daytime, and not at all on Sundays, the rate of 

 multiplication is of course much slower, and indeed 

 multiplication only takes place during the warm 

 months. For example, 1 00 rice-weevils were placed 

 in 130 grammes of wheat on April 5th, 1918. On 

 May 14th only 28 live adults were left, on June 11th 

 only 20, on July 1st, 20 ; but by August 13th the 

 number had increased to 382, and by October 5th 

 to 749. 



The most satisfactory experiments made with 

 the other species of grain- weevil (Calandra granaria) 

 at room temperature gave a higher rate of multipli- 

 cation, but again only during the warmer months. 



One hundred adult weevils were placed in 500 



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