219 



Natural enemies include a species of ScutelUsta, which parasitises a 

 small proportion of the eggs, and the larvae of the Coccinellids, Chilo' 

 corns and Exochomus, which attack those of the scale. Artificial 

 control should be carried out with a calcium polysulphide spray 

 against the newly-hatched Coccid larvae. A usefi^l formula is : 

 stone quickUme 10 lb., sulphur passed through a sieve 20 lb., water 

 13 gals. Directions are given for preparing this solution. The use 

 of a polysulphide meter is advisable and Martelli's pattern is figured. 

 The spray may be rendered more adhesive by adding 1 lb. of flour, 

 mixed to a paste and boiled, to every 20 gallons of spray. The cost 

 of spraying is much less than the loss it prevents. 



The Conservation of our Cereal Reserves. — Nature, London, ciii, no. 

 2577, 20th March 1919, pp. 55-56. 



In a recent lecture by Prof. A. Dendy it is pointed out that grain 

 stored under ordinary conditions is exposed (1) to the attacks of 

 mice and rats, (2) to those of insects and mites, (3) to those of moulds 

 and bacteria, and (4) to the process known as " heating." 



The chief insect pests in Britain are the two grain weevils, Calandra 

 granaria and G. oryzae, while in India two other beetles, Rhizopertha 

 dominica and Trogoderma Jchapra, are also responsible for much direct 

 injury. At suitable temperatures the weevils breed all the year 

 round, but in Britain normally only in the warmer months. At 

 about 28° C. (82"4° F.) a single pair of rice- weevils increased about 

 700-fold in 4 months. The accumulated excrement of the weevils 

 attracts moisture and promotes decomposition accompanied by the 

 evolution of large quantities of ammonia, and in this way the destruc- 

 tion begun by the ravages of the insects is completed. 



Airtight storage is an effectual means of preventing damage from 

 all these sources, though considerable doubt has been cast on the 

 efficacy of this method by the belief, based on inaccurate observations, 

 that the weevil is able to withstand such treatment. Experiment, 

 however, proves that all insects are more or less rapidly destroyed 

 when weevilly wheat is sealed up in airtight receptacles which it 

 nearly fills. This treatment destroys weevils in all their stages and 

 is fatal to adult mites, while it also prevents the growth of moulds, 

 and the process of heating [see this Review, Ser. A, vii, p. 24]. 



It has also been demonstrated experimentally that weevils require 

 an abundant supply of oxygen, and also that carbon dioxide, if 

 present in sufficient quantity, has a directly poisonous action upon 

 them. In pure, moist carbon dioxide they become motionless in 

 3 minutes and can remain in this condition for as much as 4 days 

 (at room temperature) without losing the power of recovery. A 

 mixture of carbon dioxide with 20 per cent, of oxygen is far more 

 fatal than pure carbon dioxide. In a mixture of 56"4 per cent, nitrogen, 

 20"36 per cent, oxygen and 23*22 per cent, carbon dioxide, weevils 

 became motionless in 43 hours at about 30° C. (86° F.), and after 

 91 hours' exposure, though 1909 per cent, of oxygen remained, none 

 revived when suppUed with ordinary air. 



When wheat is sealed up in a normal atmosphere carbon dioxide 

 accumulates naturally owing to the so-called respiration of the grain, 



(C660) 02 



