178 



Dendy (A.). & Elkington (H. D.). Report on the Effect of Air- 

 tight Storage upon Grain Insects. Part III. — Rept. Grain Pests 

 (War) Committee, Royal Society, London, no. 6, January 1920,. 

 51 pp. [Received 2nd March 1920.] j 



The chemical and physiological problems connected with the 

 destruction of insect life in hermetically sealed vessels is discussed, 

 the efficacy of this method having already been demonstrated [R.A.E., 

 A, vii, 94]. 



The results of experiments to determine as accurately as possible 

 what are the factors concerned in the death of insects in sealed vessels, 

 are summarised as follows : — Grain insects sealed up in air-tight 

 vessels, with or without wheat, succumb as soon as the oxygen has 

 been used up, a corresponding amount of carbon dioxide being 

 produced. The only gases present in such sealed vessels, under normal 

 conditions, are oxygen, nitrogen and carbon dioxide. The amount of 

 carbon dioxide given off by live wheat in air-tight vessels varies 

 directly with the moisture content and the temperature. As regards 

 moisture content there is a critical point, above which the production 

 of carbon dioxide by wheat suddenly increases very greatly. This 

 critical point varies slightly with the temperature. For the tempera- 

 ture and wheats investigated it lies between 13'25 and 16"95 per cent. 

 Above the critical point of moisture content wheat stored in air- 

 tight receptacles very soon renders itself immune to the attacks of 

 grain insects, but below this point it takes a comparatively long 

 time to do so. Data are given in the appropriate places. The amount 

 of oxygen absorbed by live wheat of low moisture content is greater 

 than the amount of carbon dioxide given off. At about 30° C, 100 

 Galandra oryzae give off about 29*5 mg. (nearly a fifth of their own 

 weight) of carbon dioxide in 24 hours, and at 20-21° C. only about- 

 9*38 mg. Weight for weight, G. granaria gives off rather less carbon 

 dioxide than G. oryzae, which is to be accounted for by its less active 

 habits. The respiratory quotient for G. oryzae is about 0-773 and for 

 G. granaria about 0'815, indicating that the respiratory processes of 

 these insects are perfectly normal. 



The complete absence of oxygen is alone sufficient to kill weevils, 

 without taking into account the presence of carbon dioxide, though 

 they are able to remain ahve for a considerable time when only small 

 percentages of oxygen are present. The extent to which weevils are 

 able to make use of oxygen in sealed vessels depends upon the per- 

 centage of that gas initially present. Carbon dioxide exerts a poisonous 

 effect upon weevils apart altogether from the question of diminished 

 oxygen pressure. Thus at 30-31° C. Galandra oryzae was killed in 

 less than 12 days in an atmosphere containing from 14"08 to 22*56 

 per cent, of CO.^, though 13-88 per cent, of O^ still remained. Pure 

 (moist) carbon dioxide is less fatal in its effects than carbon dioxide 

 with a small admixture of oxygen. Pure (moist) carbon dioxide 

 acts almost instantaneously as a narcotic, under the influence of 

 which weevils may remain motionless for a long time without losing 

 their power of recovery. 



It has not yet been found possible to devise a method by which 

 the time may be accurately estimated that is required to render wheat 

 in an air-tight silo of given dimensions and under given conditions 



