STOWAWAYS IN SHIP’S HOLD PREY ON EMPIRE PRODUCE.

Star (Christchurch), Volume XLIV, Issue 493, 30 June 1932, Page 10

STOWAWAYS IN SHIP’S HOLD PREY ON EMPIRE PRODUCE.

Poison Gas Used Against Insects That Cause Serious Economic Loss.

(From a Correspondent.) “ The human species must turn aside from its race and concentrate its intelligence on its strongest rival, the insect. .. . The insect-type has been tried out very thoroughly under world conditions, while the human species is in its merest infancy, and may be one of Nature's experiments which will fail.’’ * This remark (recently made by Mr L. O. Howard ; the chief of the United States Bureau of Entomology) occurred to me while I was being shown round the Empire’s centre of intelligence established and-equipped to fight, with all the cunning of science, one particular tribe of man’s insect rivals—those which attack and reduce the market value of Empire produce after it has left the farm, while it is on its way from the field to the factory or larder.

'J'HIS CENTRE, the Stored Products Laboratory of the Imperial College of Science at Slough, started three years ago with a grant from the Empire Marketing Board. Its object is to map out the best methods of checking this huge leakage in Empire trade. Almost every perishable crop has to run the gauntlet of infestation. Moulds change the chemical make-up of cocoa and copra, producing (in some cases) an excess of “ free fatty acids ” which bring a lower price. Insects eat little, but their mere presence is an economic disaster. Even if they only crawl over the outside of the sacks to spin their cocoons without penetrating the inside at all, they cause a serious reduction in market value. Tobacco, grain, flour, cocoa, copra, dried fruit, spices and many other products are subject to attack. Until this laboratory (a converted country house standing in spacious gardens now dotted with insect houses) was opened and placed under Professor J. W. Munro, of the Imperial College in London, there was no

institution in the Empire equipped to study these particular pests, nor was there any certain scientific knowledge of how to go about the job of checking their activities. The most fascinating part of the work at Slough is the careful, detailed study which is going on of the personal habits q$ insects. One is reminded of writing a biography of a famous man. Every little point and anecdote is carefully collected and compiled, so that eventually, out of a miscellany of facts, a complete picture can be pieced together. Scientists are trying to get absolutely accurate answers to questions such as these: How much air does one individual insect breathe? What exactly does each insect eat? (One insect was shown to feed on forty-seven different things, ranging from cayenne pepper to ship's biscuits.) In order to solve the first problem, a cunning piece of apparatus has been designed to find the exact amount of air inhaled by a single insect. The answer to this question is of practical importance because of its bearing on fumigation. Each species of insect displays a different reaction to poisonous gases. Of the two species of related moth, the cocoa moth and the flour moth, for instance, the first is considerably more difficult to kill than the second. A grain

moth, Trichogramma, withstands . all the fumigants }-et tried. This remarkable moth will also live for seven days in a vacuum and can exist for years without any food. Dr Page, the chemical expert, showed me a sort of giant incubator in which different insects, confined in bottles, were ’being gassed at various concentrations and temperatures. He has rigged this up in the original garage, which is now a veritable chamber of horrors for the insect world. He is finding out the best fumigants for each particular species of insect, and even for each stage in an insect’s life—egg, grub or adult. His work on fumigation has led to the discovery of the possibilities of a new fumigant—ethylene oxide. It is believed that this gas will be more efficient and cheaper for the fumigation of certain types of Empire produce than the mixtures at present used, and that it will have a wide commercial application. Dr Page has invented a remarkable contraption which traps typical samples of the atmosphere at various stages of the operation and which will show exactly how much

gas reaches the centre of a stack of boxes or sacks at any given time. This and other apparatus has led to some startling discoveries about present methods of fumigation. , , , With the aid of an instrument called the refractometer, which measures the light passing through a mixture of gases, it has been shown that the concentration reached by a fumigant is sometimes only onetwentieth of what was anticipated. In other words, by the time a gas reaches the inside of a pile of sacks or a stack of boxes, it is twenty times as weak as had been calculated. It has also been shown that much higher concentrations of gas are needed in winter than in summer. This suggests that under-concentration in cold weather may have been the cause of failures in the past. As many as 2,500.000 caterpillars may be introduced into a single warehouse in one shipment. If a bare dozen of these survive fumigation, a new and thriving population will arise in a few months. (A prolific housefly could have 5,598,720,000,000 descendants between April 15 and September 10 in one year). At best, therefore, fumigation can only temporarily check the trouble. Other methods are being sought through a study of the life histories of each insect.