236 



NATURE 



[April 22, 1920 



tubes has only to study his book entitled "The 

 Grand Fleet." The alloy used is a tin-brass con- 

 taining I per cent, of tin, 70 per cent, of copper, 

 and 29 per cent, of zinc. Nearly ten years ago 

 the institute took up this very problem with the 

 view of solving it, and has been assisted since its 

 inception by Sir Henry Oram and Sir George 

 Goodwin at the Admiralty. As a result, tests are 



now being carried out, in one of his Majesty's 

 vessels, of a process devised by the committee's 

 investigators, which, it is hoped, will go a long 

 way towards solving this particular difficulty. In 

 its work the committee has had no better friend 

 than Sir George Goodwin, and there is a singular 

 appropriateness about his choice as president of 

 the Institute of Metals. H. C. H. C. 



The Investigation of Grain Pests. 

 By Dr. A, D. Imms. 



FEW lines of biological research at the present j 

 time are of greater moment than those which 

 are likely to contribute towards the maintenance ! 

 of our food supply. Information comes from I 

 trustworthy sources that there is a considerable | 

 reduction in the available wheat of the world, | 

 and it is therefore more than ever incumbent upon 

 us to reduce any preventable losses to a minimum. 

 The damage sustained by stored grain through 

 the inroads of insect pests is heavy, and we 

 welcome a further series of the Royal Society 

 reports ^ which are directly concerned with 

 problems connected therewith. Prof. Dendy and 

 his colleague, Mr. Elkington, have carried out 

 much-needed observations of a more exact nature 

 than has hitherto been attempted. Embodied in 

 their reports is a good deal of both biologically 

 and economically valuable information relating to 

 some of our most destructive grain pests. In 

 dealing with the phenomenon known to the trade 

 as "webbing," they point out that it is due to 

 the wandering of great numbers of larvae of the 

 moth Ephestia elutella over the surface of heaped 

 grairi in warehouses. Each larva trails behind 

 itself a silken thread and, when very abundant, 

 the whole surface of the grain may become 

 infested with a reticulum of these threads. The 

 superficial 12 in. of the grain are affected, and 

 become fouled by faecal and other larval debris. 

 Actual injury to the grain itself does not appear 

 to be serious, and it is probable that much of the 

 contamination would be effectually removed 

 during the cleaning processes to which the grain 

 is subjected. It is, however, scarcely likely that 

 any advantage can be derived from allowing these 

 webs to remain, on the strength of a suggestion 

 that weevils are destroyed through getting en- 

 tangled therein. The safest and surest method 

 is to eliminate the pest as the authors advocate, 

 and it is noteworthy that a wide range of other 

 food products is susceptible to the attacks of this 

 species. 



In the same report (No. 4) Prof. Dendy also 

 deals with the occurrence of live insects in pre- 



1 Royal Society. Reports of the Grain Pests (War) rommittee. No. 4 : 

 ■'On the Phenomenon known as 'Wehbine' in Stored Grain." By Arthur 

 Dc-dy and H. D. Elkington. " Not? on the Occurrence of Live Insects 

 in Tins supposed to be Hermetically Sealed." By Arthur Dendy. No. 5, 

 JO19: "On til- Prevention of ''eading in Wheat bv means of Air-tight 

 Storage." Bv Arthur Dendy and H D. Elkington. No. 6, 1920: " ■'eport 

 on the F.ffert of Air-tight Storage upon Grsin Insects," Partiii. By Arthur 

 Dendy and H. D. F.lkington. Mo 7, 1920: "Report on the Vitality and 

 Rate of Mult'plica'i n of ce'tain Grain Pests under Various Conditions of 

 Temper.iture and Moisture." By Arthur Dendy and H. D. Elkington. 



NO. 2634, VOL. 105] 



sumably sealed tins. His observations show that 

 it is an evident fallacy to conclude that they can 

 survive indefinitely when once the original oxygen 

 is completely used up. The main point is to 

 ensure that the sealing of the tins has been really 

 efficiently carried out before the latter are rele- 

 gated to the store. Directly connected with air- 

 tight storage is the question of "heating." Two 

 experiments conducted by Prof. Dendy indicate 

 that this process, which is due to fermentation, 

 is prevented when the grain is stored in hermetic- 

 ally sealed vessels. Whether anaerobic fermenta- 

 tion is a factor likely to occur does not appear 

 to have been studied. In connection with the 

 investigations, it was noted that when a vessel is 

 only half filled with grain attacked by Calandra 

 oryzae, all the insects may become perfectly 

 motionless in twenty-four hours. When 273'5 c-c. 

 of air are present to lOO grains of wheat, only 

 three insects remained alive out of thirty-nine 

 (including all stages) at the end of fourteen days 

 ^t 30°-3i° C. At room temperature nineteen 

 insects out of forty-three remained alive after 

 thirty-two days. In both experiments the per- 

 centage of carbon dioxide had gone up to between 

 18 and 19, and the oxygen diminished to less than 

 2 ; and the authors express themselves as being 

 quite certain that the insects would have suc- 

 cumbed soon afterwards. 



It is evident from these experiments that 

 further research under varied conditions and de- 

 grees of infestation is still desirable. If airtight 

 storage provides ready sterilisation, without pre- 

 vious application of heat, we have a fact of first- 

 rate economic significance. An important factor 

 is the moisture content of the wheat. Above a 

 certain point the production of carbon dioxide by 

 \vheat increases very greatly. This critical point 

 varies with the temperature, and in the cases in- 

 vestigated it lies between 13-25 and i6'95 per cent. 

 Above this critical point of moisture content wheat 

 in airtight storage speedily renders itself immune 

 to insect attack ; below it a longer time elapses. It 

 is noteworthy that pure (moist) carbon dioxide acts 

 almost instantaneously as a narcotic to Calandra, 

 but is less fatal in its effects than when mixed 

 with a small quantity of oxygen. 



The seventh report deals with points in the bio- 

 nomics of Calandra oryzae and granaria, and also 

 of Rhizopertha dominica, which are three of the 

 most serious grain pests. It was found that the 



