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free from dangerous storms. Of thunder storms also there is marked variation, perhaps more than in higher latitudes. Many stations in Fiji and elsewhere have experienced several times as many in one year as in another. While many hurricanes are accompanied by appalling lightning, other equally severe hurricanes have none.

Slight changes of weather are almost constantly taking place in the tropics. A rainy spell will be succeeded by a less rainy one or by a few rainless days; a hot spell by a slightly cooler one; a spell of fitful breezes, by several days of steady winds. Such changes have been noticed by the writer in Jamaica, Hawaii, the Philippines, the East Indies, Queensland and elsewhere, but have been especially studied in Fiji. There, a study of the official records taken at Suva reveals an average of about 20 distinct spells of weather well distributed throughout the year, with about as many less distinct changes.

In conclusion, when all these types of variation occur, is it right to give the impression that tropical climates are extremely uniform? But although tropical climates are not so uniform as has been supposed, it does not follow that they are better adapted to civilized man than has been supposed. Most of the variability within the tropics is of a highly irregular sort compared with the variability characteristic of the parts of the higher latitudes where civilized man mostly lives. Indeed it appears that tropical climates are unfavorable for a high type of civilization not alone because of the high temperatures and the general lack of stimulating seasonal changes in temperatures, but also because of the often extreme undependability of the rainfall, the occurrence not infrequently of destructive windstorms and other unfavorable variations. But, nevertheless, highly civilized man can cope with the numerous problems of the tropics far better than can primitive people. Indeed, the latter, unaided, have made little progress. Hence fuller utilization of the tropical resources awaits a greater participation by civilized man.

THE POSSIBILITIES OF EXTERMINATING

INSECTS

By Dr. E. P. FELT
STATE ENTOMOLOGIST OF NEW YORK

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HIS is a special phase of the war against insects, the general

aspects of which have been discussed in such an illuminating and very suggestive manner by Dr. L. 0. Howard, chief of the Federal Bureau of Entomology, in his address as retiring president of the American Association for the Advancement of Science.1 Dr. Howard has given in this account a most excellent, summary of the broader phases of insect control, though, for some reason, possibly because he knew of the writer's interest therein, he refrained from discussing exterminative measures or the possibilities of eradicating isolated infestations.

This is something of considerable practical importance on account of the fact that more than half of our most injurious insect pests have been introduced from abroad and the process is still going on in spite of the widespread and, as a whole, well directed Horticultural Inspection Service of the general government and the various states. This latter work has undoubtedly prevented the establishment of a number of injurious insects and delayed the introduction of others, though occasionally we find a destructive pest well established in a section and in the ordinary course of events destined to extend its range and possibly inflict very serious losses over a considerable period of years.

The Gipsy Moth, the Brown-Tail Moth, the Elm Leaf Beetle, the Leopard Moth and the recently introduced Japanese Beetle are somewhat familiar examples in the eastern United States, while the south has become altogether too familiar with the Boll Weevil, the Pink Boll Worm and very lately the Mexican Bean Beetle. There is, in addition, the recently introduced European Corn Borer, now beyond any possibility of extermination so far as this hemisphere is concerned, though at one time it must have been within possibilities. We are also confronted in the early history of the Gipsy Moth with the futile attempt of the state of Massachusetts to exterminate the insect, while later developments dem

1 (a) On Some Presidential Addresses”; (b) “The War against Insects.” Science, 54: 641-651, 1921.

onstrated beyond question the practicability of accomplishing what at one time appeared to many as an unattainable ideal.

It must be conceded at the outset that problems of this nature are surrounded by manifold difficulties and that, within certam limits, each case must be decided upon its merits. In the first place, it is exceedingly difficult to determine the future status of an insect before it has become well established and thus presumably ineradicable, unless some unusual limitation makes extermination relatively easy. Granting that there is substantial agreement among scientific men as to the desirability of exterminating a given species, the great problem of educating the public to view the matter from the right standpoint and thus make possible the securing of means to prosecute a vigorous campaign still remains to be solved. Furthermore, initial operations, if the undertaking is to be successful and conducted in the most economical manner, must ordinarily be started before successful measures have been thoroughly demonstrated. There is always an element of doubt in regard to the possibility of serious injury, the feasibility of extermination and the methods to be employed, consequently it is not easy to secure a combination which will bring about the desired results. On the other hand, there is practical agreement among most scientific men familiar with the work of insects to the effect that extermination, when possible, is immensely cheaper and more desirable than the prosecution of more or less unsatisfactory control measures in a constantly expanding infested territory.

Earlier attempts to exterminate insects were based largely on some plan designed to catch or kill the last remaining insect, preferably within a year or two and certainly within a few years. Some have even advocated reducing the infested territory to practically desert conditions in such a manner as to make all insect life at least impossible. This latter is undoubtedly possible in the case of very restricted infestations and may be justified if the insect is an exceedingly destructive or dangerous one. It is out of the question if an extended area is infested or the insect one which is not particularly dangerous to life and does not threaten a basic crop or industry. Most cases come in this latter category and therefore do not justify extreme or drastic measures.

It seems to the writer that the method of progressive reduction, if one may use a special term, has not received the consideration it deserves, and yet it has been the method which has brought about extermination of Gipsy Moth colonies in areas well removed from the generally infested territory. The plan in such a case was to bring about conditions unfavorable for the multiplication of the insect and, by following up the matter from year to year, eventually reduce the numbers of the pest so greatly that natural agents or hazards actually bring about extermination. It is interesting in this connection to review the work of the earlier days against the Gipsy Moth when a systematic and very costly effort was made to find every egg mass in woodlands as well as on improved grounds and destroy them by hand, trees being climbed and walls taken down and relaid in the search for the last egg mass. This was supplemented by spraying the foliage in the infested area and banding the trees for caterpillars. Later developments have shown that much of this laborious egg hunting can be eliminated by a system of spraying and cutting out low bushes or favored food plants. Conditions are thus changed to such an extent that the insect is unable to maintain itself and eventually disappears.

Apparently, because insects are small and under certain conditions exceedingly abundant, we have failed to make allowance for the results following a great reduction in the number of individuals, especially if this be continued year after year. The matter is of more than passing importance, because there is a possibility of making practical application of the principles involved and obtaining at a relatively moderate cost resula which might eventuate in large savings by eradicating injurious species before they had an opportunity of establishing themselves over extended areas.

It may be held that the Gipsy Moth is in a class by itself and to a certain extent this is true. Nevertheless, until this method has been widely tested with a variety of insects, no one is in a position to state that it is impracticable. Even a casual study of injurious insects shows marked local variations in abundance. These must be due to some cause, and in many instances they are directly associated with agricultural practices or differences in natural conditions. The detection of such unfavorable conditions and the bringing about of similar modifications in areas where insects are destructive, is one of the opportunities of the economic entomologist and, as stated above, there is a probability of the same principle being applied successfully to the extermination of recently introduced injurious insects, provided the infested area is not too large. This last is not necessarily an insuperable difficulty. It may simply mean a better organization and an extension of operations over a longer period of time.

If we turn from the field of entomology to the broader realm of zoology, and consider what has occurred in the case of larger forms, we may find some very suggestive hints. It should be noted in this connection that in not a few instances the apparently impossible has been brought about by the irresponsible urge of self interest and not through carefully directed cooperative efforts for the attainment of a definite aim.

One of the most striking instances of this kind is the extermination of the Passenger Pigeon, a bird at one time so extremely abundant that three carloads a day were shipped from one small Michigan town for a period of forty days. The Great Auk, the Labrador Duck and the Pallas Cormorant have passed into history. The Whooping Crane, the Trumpeter Swan, the American Flamingo, the Heath Hen and Sage Grouse are representative of a series of valuable and interesting birds doomed, in the opinion of Dr. Hornaday, to early extermination.

Large herds of Buffalo were saved from extinction at the last moment through the intervention of naturalists interested in preserving the wild life of the country. The Prong-Horned Antelope, the Big-Horn Sheep, the Mountain Goat and tho Elks are traveling the same path as the Buffalo.

The depleted salmon, shad and herring fisheries, the necessity of protecting both the oyster and the lobster and the great scarcity of certain whales have been brought about by artificial agencies, though it would seem as if inhabitants of the water would have a better chance for escape from a persistent human enemy than would be the case with terrestrial forms.

It is true that these unfortunate conditions have resulted through specific peculiarities or limitations which made attack at certain points particularly effective, such as killing birds when migrating or in their nesting retreats or the wholesale catching of spawning salmon. Those dependent in large measure for their living upon some of these forms could not believe that the natural prolificacy of the species would not offset almost any levy by human or other agents. Are we not unconsciously assuming that because insects are apparently innumerable, systematic general measures continued over a series of years are foredoomed to failure? It by no means follows that immense numbers indicate impossibility of control or extermination.

The stimulus of a deadly peril is sometimes necessary to demonstrate the practicable. This has occurred in the case of yellow fever and, while the insect carrier was not exterminated, it was soon found entirely possible to greatly reduce the breeding of the “day mosquito" and by a combination of mosquito control measures and preventing insects from gaining access to infection, the disease was actually eradicated. The deadly peril of plague on the Pacific Slope drove home the lesson that safety lay in rat eradication and that this latter coula be accomplished only by a simultaneous attack upon the rat, its food supply and habitations. This was carried to the extent of exterminating rats over considerable city areas. Given adequate incentive, there appears to be no prac

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