180 



and none out of 100 Rhizopertha dominica recovered. Rhizopertha 

 dominica is less susceptible to high temperatures than the two weevils, 

 the lethal temperature for an exposure of three minutes being about 

 146° F. for the former and between 120° and 131° F. for the latter 

 (in the adult condition). An exposure to a temperature of 145*5° 

 F, for five minutes is sufficient to kill the larvae of Calandra oryzae 

 and probably to sterihze the wheat completely as regards all insect 

 life. Although a moist atmosphere is undoubtedly more favourable 

 than a dry one for the two weevils, both species can live and multiply 

 in a dry incubator, Calandra oryzae increasing much more rapidly 

 than C. granaria, provided the initial moisture content of the grain is 

 sufficiently high. Very dry wheat is less Hable to attack by weevils 

 than wheat with a moderate or high moisture content, but wheat 

 readily absorbs moisture in a damp atmosphere, and thereby becomes 

 much more susceptible to weevilling. Rhizopertha can withstand dry 

 conditions better than either of the two weevils. Calandra oryzae , 

 and C. granaria are both hkely to be serious pests in the British Isles, 

 but little is to be feared from Rhizopertha dominica under ordinary 

 temperature conditions. In addition to the damage done by actual 

 consumption of the grain the presence of weevils results in extensive 

 fouhng with faecal matter, encouraging the absorption of moisture and 

 the ultimate rotting of the whole mass. In large quantities of wheat 

 the process of decay is doubtless accelerated by rise of temperature 

 due partly to the presence of insects and partly to " heating of the 

 wheat." 



Rathb.one (H. E,.). Wheat and its Pests. — Grain Pests {War) Com- 

 mittee, Royal Society, London, Memorandum no. 6, December 

 1919, 4 pp. [Received 2nd March 1920.] 



Before the War the problem of wheat storage was of but httle interest 

 in Great Britain^ as wheat was practically never stored in large quantities 

 for any length of time. During the War, when storage became a 

 necessity, considerable trouble was experienced from mites. W th 

 regard to weevil infestation, the author expresses the opinion that the 

 loss of wheat from weevils all over the world would probably be 

 overstated at 0-001 per cent, per annum. It has been stated that 

 severe losses were incurred by the Government in purchasing during 

 the War a larger amount of wheat in Australia than they were likely 

 to be able to ship ; in the author's opinion the loss to the British 

 Government will be small (certainly less than 2 per cent.), the smallness 

 of the loss being largely due to the measures initiated to combat 

 insect infestation {R.A.E., A, vii, 167]. The standard plant finally 

 erected for sterilising and screening the wheat is described. This 

 is capable of treating 1,000 bushels per hour. All weevi s, eggs and 

 larvae are killed in passing through the steriliser ; from 200 to 300 lb. 

 of dead weevils afe secured from the amount of wheat (2,500 bags) 

 treated in eight hours, about 442,000 weevils being estimated to the lb. 

 While heavy losses have occurred in Australia; it is pointed out that the 

 conditions under which an enormous bulk of wheat was obhged to 

 remain stored for some years were quite exceptional and are very 

 unhkely ever to recur. 



