February, '19] CHAPMAN: INSECTS IN FLOURS 69 



cereals has consisted of experimental work in the laboratory and obser- 

 vational work in storehouses. The experimental work has proceeded 

 on the assumption that other things being equal, susceptibility may be 

 due either to the attraction which a cereal may offer to insects, influ- 

 encing the number of insects which might invade it in the first place, 

 or to the rate of development of the insects after entrance, which 

 might result in an accumulation of the insects in great numbers. 



In the study of the invasion, the various flours were placed in cylin- 

 drical jars with removable partitions, which divided each jar into five 

 equal sectors. A different flour was placed in each sector, the par- 

 titions were removed, and the insects were placed in a depression in the 

 center of the jar. Being thus surrounded by equal amounts of the 

 different flours, the insects were free to express a choice if they had any. 



The experiments were carried on in the dark and extended from a 

 few hours to several days, the length of time making little difference 

 after the first few hours, when the insects were exploring about. When 

 an observation wag to be made, the partitions were replaced and the 

 contents of each sector removed, to count the insects contained in it. 

 When one hundred insects were used in the experiment, the number 

 found in a given cereal would be the percentage of relative suscepti- 

 bility of that cereal as compared with the others used in the experiment. 



The relations of Tribolium confusum to five grades of wheat flour 

 and various wheat flour substitutes were studied in this way. The 

 results of 25 experiments with adult beetles showed the following per- 

 centages: 1st Sizings, 10.6 per cent; 1st Middlings, 11.5 per cent; 

 1st Low Grade, 12,4 per cent; 1st Tailings, 14.6 per cent; 5th Bran, 

 52 per cent. The coarseness of these flours varies in the order named 

 from the fine sizings to the bran. The experiments with larvae did 

 not show a variation greater than 7 or 8 per cent on either 

 side of 20 per cent, the expectation, and consequently show no pref- 

 erence, for an average of about one-fifth of the total number of larvae 

 were found in each sector. 



The results with the wheat flour susbtitutes showed no percentages 

 constant enough to denote decided choice, either among the various 

 substitutes or as compared with low grade wheat flour, so long as the 

 coarseness remained about equal in all cereals. When the bran from 

 rye meal was introduced into the experiments a decided percentage 

 was noticed. It contained an average of 36 per cent of the beetles and 

 was very constant, while the percentages found in the other portions 

 were small and subject to greater variation. When coarse corn meal 

 was used, no increase in percentage was found. 



It seems, therefore, that a coarse, flaky material is more attractive 



