Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

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Monograph

Identifikator:: 1738588467

URN:: urn:nbn:de:zbw-retromon-115043

Document type:: Monograph

Title:: Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

Place of publication:: Nairobi

Publisher:: East African Standard

Year of publication:: 1926

Scope:: VI, 337 Seiten; Ill.

Digitisation:: 2020

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Etomology & Mycology

Collection:: Economics Books

PART 1IV. difficulty. As an example of what can be done by legislation to increase the numbers of an insectivorous bird, and at the same time as a still better example of what should not be done in the way of indiscriminate protection, may be cited the case of the Buff-backed Egret (Ardea Ibis) in Egypt (6)+ This bird was abundant twenty-five years ago, but by 1912, owiny to its having been killed off by plume hunters, only two small colonies of a few pairs each remained. A law was then passed for its complete protection; by 1920 there were at least 100,000 in the country, and by 1924 perhaps nearly a quarter of a million. By this time the bird had become a serious nuisance in several ways, and doubts were entertained whether it was really as beneficial as had Leen stated in destroying the Cotton worm (Prodenia litura) and other pests. An investigation was therefore undertaken, and the stomachs of numerous birds examined at short intervals over a period of a year. Not one single cotton worm was found in any of the stomachs; the only pest of importance on which the bird fed in quantity was the cutworm (Euzoa ypsilon), while even the good it thus did was probably rendered nugatory by the fact that it also devoured in numbers the most useful parasite of the cutworm, as well as other beneficial animals and insects. The utilisation of the smaller forms of life—insects, protozoa, fungi and bacteria, which may be enemies of an insect pest, naturally presents more difficulties, and cannot be effected simply by the passing of a law. The most obvious method is the introduction of a beneficial organism from a foreign country; and while there have been notable examples of success, as for instance the introduction of the lady-bird Novius cardinalis into California to control the Fluted Seale of Citrus (Icerya purchasi), the greater number of attempts turn out to be failures. This may be due to unfavourable climatic conditions in the new country, but perhaps more often the failure is due to some less obvious cause which cannot be ascertained until the experiment has been made. Thus the lady-bird known as the Mealy-bug Destroyer (Cryptolemus montrouzieri) has been introduced from Australia into numerous countries, among which may be mentioned the United States, Egypt, and Kenya. In none of these countries has it been able to maintain itself naturally, though in all three it thrived and bred abundantly in the Laboratory. In America, except in a few small areas, the adverse condition appears to be climatic (8, p. 114)1, the winters being too cold for the mealy-bugs to breed, but not cold enough to force Cryptolemus to hibernate: consequently the lady-bird dies out during the cold weather from scarcity of food. The practice in those parts of America is therefore to breed enormous quantities of this lady-bird artificially, and to liberate them each year, a practice which is only economically possible on a very large scale, and in a country where plenty of skilled labour is obtainable. In this country and in Egypt, although the climate is favourable, Cryptolemus never appeared to survive after liberation for more than a very short period. In both cases this was due to their being attacked by ants attending the mealy-bugs; consequently the system of yearly liberation as practised successfully in parts of America, would be useless in either of these two countries (even were it practicable on the score of expense and available labour) unless something were also done to control the ants. ' See list of references on page 194. 187

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