Insects versus Men

Dominion, Volume 23, Issue 75, 21 December 1929, Page 21

Insects versus Men

The War on the

Farmers’ Enemies

THE world’s history needs to be rewritten in terms of insects, writes Mr. James E. Boyle, Professor of Rural Economy at Cornell University (U.S.A.). Who will tell what'the yellow fever mosquito, for instance, or the cattle tick, of the tsetse fly has done to the human race? There are estimated to be over 400 million kinds of insects in the world, and all of them arc of significance to mankind. These insects are all our competitors for the world's limited food supply. Who shall inherit this earth, man or insect, will depend in the last analysis on which creature is most efficient in securing his daily ration. , When we remember the insects capacity to reproduce, we begin to feel uncertain about our own future survival. Consider, for instance, the tiny green cabbage aphid. Under favourable conditions, there are 30 generations of these in one year. The mother aphid who lays her eggs the first of April becomes the progenitor of 12 generations by the middle of August. She produces 41 young in one generation, therefore, by the middle of August, if all the mother-aphid descendants should live, there would be alite at one time some 560 quadrillion aphids I Or to state it more exactly, 564,05 - -257,509,154,652 aphids. And they would weigh about eight times as much as all the human inhabitants of this globe.

This shows rather strikingly what one mother aphid can do in four and one-half months, if she has plenty of food and no enemies. We must also remember the size of the insect's appetite—-especially when in the larva stage. Familiar examples ’of the larva are the maggots—children of the common house fly—and the caterpillars, grub worms, and so on, children of the butterflies and moths which play like fairies in the sunlight or moonlight. The sole business of the larva is to eat and grow. And so we find that the caterpillar of the common Polyphemus moth consumes, in about 56 days, 86,000 times his original weight. This is rather terrifying! 1 Still, the balance has been maintained, thus far, between man and insect, so that the latter has not yet deprived his human competitors of too much of their food supply except in the cases of insect plagues. Will man or insect inherit the earth? If it is a question of the survival of the fittest, then the argument favours the insect. The cockroach, for instance, was here a million years before man came; therefore he will likely be here a million years after man has joined the dodo. The cockroach came with the coal age. He is versatile. Living first in Asia, he travelled by ship to Holland, and later became at home all over Europe. While he prefers the warm climate, he is found in numbers among the Laplanders in the far north. He often destroys quantities of the dried fish they put away for winter. More famous, however, are the cockroaches of Brazil. Here a traveller reports seeing children with their eyelashes more or less eaten off by cockroaches. The eyelashes are bitten off irregularly, and in some places quite close to the eyelid. Since Brazilian children naturally have the beautiful drooping lashes of the Latin races, their appearance was strangely defaced. These same cockroaches also bite off bits of toenails. Apparently they confine their depredations to children.’

As the cockroach has migrated all over the world, so, too, many other insects are doing. Man’s scientific means of insect control is offset by the modern means of travel which the insect now uses. When Lindberg' finished his 46.000-mile flight, touching three continents and dozens of countries, think of the scores of new insects he picked up and brought back to the United States. And one female insect —even an egg—is enough to start a new pest.

Whence come our present insect pests? Most of them come from foreign countries. Thus they leave behind their natural enemies, and. with plenty of rich food, they show us what the mathematical formula of geometric progression looks like when put into practice. In the 70's an insect from Australia, the cottony scale, threatened the speedy aud absolute extinction of the citrus industry in California. The counter attraction launched by our Department of Agriculture was one of the most spectacularly successful jobs ever done in the field of entomology. But the battle was not the work of a year. The insect had to be traced to Australia. Then a seasoned insect hunter was sent to Australia to spy out these insects and to collect specimens of its enemies. This entomologist, Mr. Albert Koebele, found a little ladybug with'a voracious appetite for this one insect. He succeeded in bringing specimens alive on the long voyage across the equator—a very difficult feat. When these ladybugs were tried out on an infested orange tree the result was a glorious triumph for the scientist. The Australian ladybugs fell on the cotton scales with such avidity that the problem was solved. No other insect tried in international work has been such a success.

Next to this achievement stands our success in saving the Hawaiian sugar crop from annihitation at the hands of the Australian cane-leaf hopper. Again the natural enemy of the hopper was found and successfully brought to the scene.

These two brilliant successes in overcoming, our insect enemies bad one undesirable effect; they created a sense of false security in the minds of the general public. The feeling became general that our proficient entomologists could always solve the problem. The fact remains that in only a few conspicuous cases have we won the battle against the bug. We have > already surrendered to the chestnut blight, and these noble and useful trees are fast becoming extinct. The American Congress last year spent ten million dollars in the corn-borer campaign, and the total effect was to mitigate very slightly the ravages of this pest. The corn borer will undoubtedly continue his march until the whole corn belt is covered, and we shall pay his perpetual tribute in the form of a few hundred million bushels of corn a year. This pest has never been stopped yet in any country. We have already learned to live with the Hessian fly, who came over with the mercenary troops during the Revolution. We have already paid him tribute of hundreds of millions of bushels of wheat, and shall keep on doing so.

The Mediterranean fruit fly was discovered in Florida early in 1929. It travelled rapidly west, and now definitely threatens the citrus industry of California.

The cotton boll weevil arrived in Texas in 1892 from Mexico. This insect has now definitely established himself in every cotton state except California. He is with us as a permanent boarder. The fight will continue against him. as against the corn borer, not to exterminate him, but to keep him within bounds.

We multiply our scientific means of overcoming harmful insects. But as fast as one bug is destroyed two new ones take his place. Our worst pests to-day were unknown to our grandfathers, and our gandchildren may struggle with new and more harmful insects than we know. Even at the present moment entomologists estimate that they are acquainted with one kind of insect out of eight to ten. How the battle between insects and men will swing in the future it is impossible to prophesy.