11 



than that species, it is capable of doing considerable damage and render- 

 ing flour unfit for use. It apparently occurs most commonly in flour that 

 has been kept for some time. A sample of flour, said to have been 

 packed in hermetically sealed tins and examined four years later, 

 was found to be heavily infested by this mite. Excessive moisture 

 seems to favour the propagation of H. entoniophagus, and individuals 

 in all stages of development were able to live for eight weeks floating 

 on the surface of water, and for about two weeks when entirely 

 submerged in it. 



Glyciphag'us fuscus, Oud., was found in only one sample of flour, 

 and occurred very sparingly in association with T. farinae. Botli 

 male and female are described. 



Experiments have been carried out with T. farinae only, as it is 

 by far the most important species, and any treatment that would be 

 effective against it would probably prove successful against the others. 

 In previous experiments [loc. cit.'\ it was found that the minimum 

 amount of moisture necessary to the existence of mites in flour was 

 between 11-5 and 12-5 per cent. Further results were obtained by 

 drying about 5 grams of flour in a steam oven for 24 hours. It was 

 found that in flour with a moisture content of 13 per cent, the mites 

 increased rapidly in numbers ; with a moisture content of 12-4 per 

 cent, the increase was relatively very slow; with 12-2 per cent, 

 moisture they were gradually exterminated in two or three weeks. 

 Below this moisture content the mites perished quickly. The minimum 

 moisture content necessary for existence of the mites is therefore about 

 12-3 per cent., so that if 11 per cent, be taken as the maximum per- 

 centage of moisture permissible in stored flour there is a small margin 

 of safety. The previous finding, namely, that a temperature of 120° F. 

 for about 12 hours is the minimum temperature required for the 

 destruction of all mites and eggs, was confirmed by further experiment. 

 With regard to hermetical sealing, it was found that even after two 

 months a few mites reappeared in jars so sealed, though care had been 

 taken to avoid re-infestation. 



A series of experiments was carried out to test the effect of passing 

 infested flour through sieves of bolting-silk. Some eggs were able to 

 pass through the finest silk used, which had 200 meshes per lineal 

 inch, and this sieve was quite ineffectual in removing the faecal pellets 

 which conduce to rapid decomposition of the flour, while much of the 

 flour itself would not pass through such a sieve. In flour stored in an 

 atmosphere of almost pure carbon dioxide for periods up to 50 hours 

 the mites remained inert while the gas was present, but quickly became 

 active again when the treatment was discontinued. 



It is obvious that preventive measures are more desirable than 

 remedies, owing to the production of large quantities of faecal matter, 

 which it is impossible to eliminate from the flour. The most satisfactory 

 method of preventing infestation is only to store flour the moisture 

 content of which is below 11 per cent, in the temperate zone, and 

 much lower in tropical countries. The usual amount of moisture 

 present in commercial samples is between 12-5 per cent, and 14 per 

 cent. ; it would therefore be necessary to submit to a drying process 

 an}^ flour that it was intended to store for any length of time. Such a 

 method as that of the Hess Drier and Cooler previously described 

 [loc. cit.'] has given success with wheat and should be more easily 

 applied to flour ; it has the additional advantage of preventing 

 re-infestation, which very easily occurs in flour that has merely been 

 heated in order to kill the mites. 



