FEASTS IN LILLIPUT

Evening Star, Issue 20217, 3 July 1929, Page 4

FEASTS IN LILLIPUT

WHAT DO INSECTS LIVE ON ? Science is sotting itself to _ discover what insects eat. Much less, it seems, is known about insect nutrition than a layman would, perhaps, have assumed. Even the diet needed by larvae of the common house fly is not precisely understood. Insects (ofwhich there are more kinds than of any other group of living creatures) destroy approximately 10 per cent, of the world’s crops and 20 per cent, of the crops of the tropics. The size of their appetites in the aggregate is not, indeed, in dispute. Tint the insects’ “ psvchologie du gout ’ remains to be written. Now, taking the beetle by the horns (to use an expression common, no doubt, among scientists), it has been decided to apply the arts of Brillat-Savarin to the science of entomology. What, more literally, is now being sought is exact information as to the- digestive requirements and processes of insects. The more that is 'known in this largely unexplored field the less bewildering will be the ’task of guarding crops and flocks and herds from the ravages of insects. _ It is this fact that has just led the Empire Marketing Board to make a grant to the London School of Hygiene and Tropical Medicine for the carrying out of an inquiry into problems of insect nutrition, states a correspondent of the ‘ Manchester Guardian.' The hoard has acted on the recommendation of the Committee of Civil Research which, under the chairmanship of Lord Balfour, is impressed with the great potential economic value of research on these lines. Such information as has already been gathered shows that in many cases insects choose their food mainly on chemical grounds. Cabbage butterflies, for example, oat cruciferous plants because they like the flavour of the mustard oils present in members of this family; tortrix moths live on beeches, chestnuts, and oaks, partly because these trees contain a spice of tannin, while the apple worm will bore right through the pulp of the fruit and devour seeds at the core, and in so doing it balances its ration with more protein.' Similarly, insects may be repelled by the presence of certain obnoxious chemicals in their host plant. Termites, which- attack tunber in the Philippine Islands, will, for instance, refuse to eat teak and cypress as a protest against alcohols which create discord in their digestive harmony. The woolly aphis, to mention a more familiar insect, prefers apple trees growing on fairly alkaline soils

to those in a more acid solution. Many scattered facts have thus been collected, but their possibilities have never been more; fully explored. The inquiry is made more involved by the very wide range of appetite possessed by insects. Some can llouri.sh on pure cellulose, ordinarily the most indigestible of ail food constituents. They have lived for months on a diet of undiluted cotton wool, building up proteins without, apparently, eating any nitrogen. But in this ease research has shown that the insects do their digesting by proxy. They keep inside them a population of 'protozoa (■formerly regarded merely as parasites') which arc detailed to attack the cellulose and make it digestible. When these protozoa arc artificially removed the insects continue to eat wool, but die from failure to digest it.

The volume of unclassified evidence available is adequate only to bring out the necessity for systematic research. Old classifications are no longer accepted. The rough division of insects according to what they were believed to feed on has been proved quite unsatisfactory. Thus it is now recognised that many lumber-boring insects do not cat wood, but burrow into it in search of fungi growing between the cells, 'flic ambrosia beetles, which belong to this class, actually cultivate crops of a minute fungus and reap them at regular intervals, almost in the manner of a mushroom farmer. A special apparatus enables the beetle to transfer fungus spores to new pastures when it wishes to increase its acreage under cultivation. The investigation now about to be launched may approach its task from various angles. A study of the chemical constitution of flies and larvro will throw light on the fate of the food which is swallowed. The detailed anatomy of the organs of digestion and the * chemistry of digestion are other subjects that invite inquiry. A series of questions require answers. Do the maggots of flies live mainly on the bacteria which swarms on meat or upon some part of the meat itself? Can larv® be reared on synthetic diets, or on meat deprived of some part of its normal constitution, or on bacteria without meat? What are their minimum requirements? The technicality of these problems does not rob them of urgent practical and economic importance. They are large and complex, hut work upon them may well pave the way to more efficient control of many of the insects that every year cost producers (and therefore consumers) all over the Empire many millions sterling.