INSECT CONTROL IN FLOUR MILLS, 27 



inaccessible to the gas and escape treatment only to restock the mill 

 later and offset the large numbers of their species killed during the 

 fumigation. 



Frequency of Fumigation. 



Most millers who fumigate with hydrocyanic- acid gas apply the 

 treatment once a year. Certain millers fumigate in the spring, give a 

 second fumigation during midsummer, and a third during early fall. 

 A more effective plan is to give two fumigations in July or August 

 within three or four weeks of each other. Of the different stages 

 of the moth, the egg stage is the most difficult to kill, and a certain 

 number of eggs usually escape the first fumigation. If, then, a 

 second fumigation is applied three to four weeks after the first , it 

 will catch the worms that hatch from the eggs unaffected by the first 

 fumigation, when they are in a stage easily killed by the gas ; at that 

 time they have not had an opportunity to develop into adult moths 

 and lay more eggs. Fumigation is advocated only for the warm sum- 

 mer months. 



Effects of Hydrocyanic- Acid Gas Upon Flour. 



Experiments conducted at the Kansas Agricultural Experiment 

 Station^ results of which are published in Bulletin No. 178 of that 

 station, included fumigations of four grades of soft winter-wheat 

 flour, consisting of a patent, a straight, a clear, and a low grade, and 

 of three grades of hard winter wheat flour, consisting of a patent, 

 a straight, and a low grade. Samples were fumigated at the maxi- 

 mum strength recommended for flour-mill fumigation, viz, 1 pound 

 of cyanid to each 1,000 cubic feet of space. Flour was exposed to a 

 temperature of 90° F in a tight chamber kept at constant temperature 

 for a period of 12 hours. Dean, of Kansas, concludes : 



It is only in the careful measurements employed in the test that any differ- 

 ence between the fumigated and the unfumigated flour is apparent at all. The 

 only notable difference appears in the maximum volume of the dough in the 

 test made immediately after fumigation, but not after thirty days. The finished 

 loaf shows no deleterious effect from fumigation in any of the tests. 



CONTROL BY HEAT. 



It has been stated that fumigation with hydrocyanic-acid gas, 

 effective as it is in controlling the Mediterranean flour moth in mills, 

 does not control so satisfactorily the several stages of the flour beetles 

 (Tribolium confusum Duv. and T. fei^rugineum Fab.), the "bran 

 bug" (Laemophloeus minutus Oliv.), the cadelle (Tenehroides mau- 

 ritanicus L.), and the sawtoothed grain beetle {Silvanus surinam- 

 ensis L.) These insects are naturally more resistant to the effect of 

 gas. and secrete themselves in large numbers in cracks and accumu- 



