WAR ON PESTS

Otago Daily Times, Issue 18758, 11 January 1923, Page 6

WAR ON PESTS

RABBIT-KEEPING TO PREVENT MALARIA. HOW TO EXTERMINATE DEADLY INSECTS. A great many useful animals are now extinct, thanks to the activities of man. This lieing the ce.se, it is odd that move attention has not been paid to the extermination of pests. We fight them locally, enough to got the upper hand for the moment, but there are always plenty left. Dr E. P. Felt, State Entomologist of New York, in an article on “The Possibilities of Exterminating Insects.” contributed to the Scientific Monthly (and quoted by the Literary Digest), calls attention to the fact that vest numbers do not necessarily preclude extinction. Witness the well-known case of the American passenger pigeon. We have done away with this useful creature in its multitudes; why should we despair of wiping out the boll weevil or the cattle tick? Dr Felt admits that we cannot get at the last insect and step on him, but- he believes that numbers may in ell cases be reduced so greatly and conditions be made eo unfavourable that the remaining pests will die off from natural causes. Ho writes: ‘ There is practical agreement among most scientific men familiar with the work of insects to the effect that extermination, when possible, is immensely cheaper iand 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 witl'/n 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 one. 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 colonics in areas well removed from the generally infested territory . The plan in such a case was to bring about conditions unfavourable for tbe 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.

“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, especi»llv if this be continued year after year. Until this method has been widely tested with a varietv 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 unfavourable conditions and the bringing, about of similar modifications in areas where insects are destructive is one of the opportunities of the economic entomologist. WHAT HAS BEEN DONE.

“If \re consider what lias occurred in tils case of larger forms, we may find some .very suggestive hints. It should he noted in' this connection that in not a few instances the apparently impossible lies been brought about by the urge of self-interest. 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 car loads a day were shipped from one small Michigan town for a period of 10 days. The great auk, the Labrador duck, and the Pallas’s cormorant have passed into history. The whooping crane, the trumpeter swan, the American flamingo, the heath hen, and the sage grouao 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 the elks are travelling the same path as the buffalo. The depleted salmon, shad, and herring fisheries, the necessity of protecting both the oyster and tho lobster, and the great scarcity of certain whales have been brought about by artificial agencies.’' Tho stimulus of a deadly peril is sometimes necessary to demonstrate the practicable, Dr Felt pointed out. This has occurred in the case of yellow fever. By a combination of mosquito control measures, and preventing insects from gaining access to infection, the disease has been actually* eradicated. The peril of plague on the Pacific Slope drove home the lesson that safety lay in rat eradication, and a simultaneous attack upon the rat, its food supply, and habitations was carried to the extent of exterminating rats over considerable city areas. Ho continues: “The studies of bark beetles by Dr Hopkins have shown the possibility of securing very efficient control by simply reducing their numbers, in some instances by 75 per cent., to such an extent that those remaining would be unable to overcome the natural resistance of the tree. A concrete application along these, lines is found in the attempt of recent years by tho United States Biological Survey to destroy predatory animals, such as wolves and coyotes. The work is organised on a co-operative basis, with Stale and local associations, and as a, consequence losses have been practically ended over groat areas of the most valuable summer and winter sheep ranges, and reduced in othcLS to very small amounts compared with earlier years. ANIMAL PROPHYLAXIS.

" The systematic destruction of prairie dogs has resulted in over four million acres of public lands being ‘largely freed’ from these pests. There hae also been very effective work against pocket gophers and rabbits. The work of Mr W. F. Fisko upon the tsetse fly has shown that it is only necessary to reduce the infestation by this pest to moderate limits in order to secure a very satisfactory degree of freedom from the deadly sleeping sickness. The studies of M. Roubaud upon malaria in Franco indicate an intimate connection between this infection and the number of mosquitos per host. “The author suggests what he calls animal prophylaxis—that is, the importation of enough cattle in certain areas to attract the insect, and thus protect man to a large extent. The keeping of rabbits has been ad-, voented more recently as a protection from malaria, and may be regarded as a variant of M. Rouband’s plan. All are forms of percentage reduction, a step which under certain conditions might be continued to the vanishing point, at least, so far as the infection is concerned.

“We note the progressive extermination of the cattle tick from nearly 500,000 square miles of territory, and the consequent elimination from this area of a very serious infection. It was apparently an impossible undertaking until the decisive factors were ascertained. In this connection it might bo stated that gratifying progress has been made in demonstrating methods of controlling the Rocky Mountain spotted fever tick, a carrier of a deadly human infection.

“It is evident that the elimination of a certain residuum may safely be left to the operation of various natural causes. This latter is an extremely important factor in any attempt to exterminate insects, since it is usually impossible to destroy the last individual or' to bring about conditions over an infested area of some extent which would make the existence of insect life impossible.''

Some touches of unconscious humour have enlivened the story of their trials and troubles by Auckland soldier farmers to the investigating board recently appointed to report upon their affairs. One ex-soldier, in narrating his “misfortunes,” said that, whereas he and his wife, although married for several years, had no children when llioy took up their farm, they now had two. When the members of the hoard visited the farm they saw two of the healthiest and most attractive ‘‘misfortunes’’ that any

couple could wish for (reports the Mew Zealand Herald). Incidentally, it has been noted by tho board that bonny children are very plentiful on moat of the farms visited by them. When anyone becomes a Freeman of the City of I/ondon he has certain advantages which do not come the way of tho man in tho street. He is eligible for appointment to the office of alderman, sheriff, or common councilman, and may, if ho can prove necessity, enjoy tho benefits of certain charities. Tho Freedom of tho City may he obtained in four different ways —servitude.

redemption (or purchase), patrimony, or honorary presentation (or gift of the city). To be admitted by servitude a man must complete an apprenticeship with a freeman, according to the customs of the city ; freedom by redemption necessitates certain Tees being paid to the Chamber of London, after (he candidate has attained his majority. Admission by patrimony means thul a child of a freeman, whether a boy or girl, may gain the freedom of the city, when he or she is 21 years of age, provided that the approval of the Court of Common Council is obtained. Honorary presentation is usually made to distinguished people on a resolution of tho Court of Common Council. Women, says “Debrot.t’s City of London Book.” whether unmarried or widows, are admitted to tho freedom in tho same way and on the same terms as men, but they are suspended when married.