6o REPORT OF THE STATE ENTOMOLOGIST I92I 



degrees. The work of R. M. Chapman x shows that from 40 to 50 

 days or even longer are required at temperatures ranging from 

 about 73 to 84 degrees F., a considerable extension of the later 

 developmental periods being due to differences in the food available. 



Our data show an extended adult existence, in Jar E it being 

 at least 148 days and in jars F and G 217 days, with no indication 

 that these are the maxima. It should also be noted that although 

 the life cycle in our breeding jars was completed in from about 

 50 to 90 days, there is no marked indication, except possibly in the 

 case of jar G, of a second generation and this did not appear until 

 into December or about 5 months after the first generation of 

 larvae. 



This suggests periods of inactivity between generations and con- 

 sequently estimates of the number of generations annually based 

 upon the time required to complete the transformations are inac- 

 curate because no allowance is made for this interval. This con- 

 dition may easily exist and be obscured to a very considerable 

 extent by apparently constant breeding, owing to the overlapping 

 activities of different individuals. The increase in our breeding 

 jars was less than anticipated. This may be explained in part by 

 the limited amount of food and the probability that some of the 

 smaller larvae were devoured. It is certain that dead beetles were 

 dismembered and it was therefore practically impossible to account 

 for all adults, unless there were repeated separations into smaller 

 groups. The low rate of multiplication could not have been due 

 entirely to the lack of food because after two and a half years the 

 flour was still in a somewhat fair condition, though decidedly con- 

 taminated, and this was true even in the jars containing the most 

 insects. It is worthy of note that a living beetle was found in jar 

 D and a living larva in jar F, November 24, 1920, about 30 months 

 after the breeding was started. Nothing was alive in the other jars. 



The figures obtained by Mr Chapman * show that individual pairs 

 during a period of 42 days may produce from seven to as many 

 as 50 larvae, the normal probably being nearer the higher than the 

 lower figure. He also attempted to determine the influence of 

 nutrition' in affecting the liability of infestation and came to the 

 conclusion that the coarseness of the product was a more important 

 factor, since the beetles could more readily penetrate flaky materials. 

 He found that the percentage ratios between coarse and fine bran 



1 Minn. State Ent. 17th Rep't, 1918, p. 73-93. 



