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 IV. There remains the utilisation of the indigenous enemies of a pest, which presumably controlled it effectively before the time when, with the growing of a crop on an extensive scale, it had the opportunity to become a pest; and which may well be hoped to control it again, provided that the complicated inter-relations of these beneficial insects with their enemies, and of these latter with their parasites and predators to a third and even fourth degree, can be satisfactorily understood. The problem of the Common Coffee Mealy-bug in this country affords a good example of what may be possible in this direction. Tae Common Corree MEaLy-Bua. At least five species of true Mealy-bugs of the genus Pseudococcus occur on coffee in this Colony. Only one of these, the most abundant and the most dangerous, will be dealt with here. This is a species which has been identified as Pseudococcus citri, Risso, a species which is almost cosmopolitan, and has been recorded from coffee in other countries, but is more usually known as a pest of citrus. In this country not only is it never found on citrus trees, even when these are growing actually among infested coffee, but it is unable to survive when artificially transferred to citrus. It would therefore appear that even if it is anatomically indistinguishable from the true P. citri, it is at least a distinct biological species. At first sight this might seem to be a point of scientific interest only, but in reality it is of the utmost practical importance. For instance it is now just as necessary to guard against the introduction into the Colony of the citrus-feeding form of P. citri, as if no form of this species were already present. Again it is more than likely—though one cannot be certain on this point—that it would be useless to attempt to introduce any internal parasite of the citrus-feeding form in the hope that it would control the coffee-feeding race. It may be mentioned in this connection that a species of Pseudococcus very similar to the coffee-feeding one, has been found in the Ruiru district of Kenya living on a wild shrub; this mealy-bug is very heavily attacked by a parasite which can not be induced to parasitise the coffee mealy-bug. The Common Coffee Mealy-bug has been known to exist in the Colony since 1909 (1, p. 98)+ and is probably indigenous. It breeds on a number of other plants, both cultivated and wild, in addition to coffee; but it is a matter of some difficulty to make a complete list of its host-plants, as not only must miscroscopical preparations be made of a mealy-bug found living on some other plant, to find out if it is the same systematic species, but it is also’ necessary to determine by experiments whether or not it is capable of living on coffee, to ascertain whether it is the same biological species. It is only within the last three years or so that the species has spread to an alarming extent, and it is now to be found widely distributed over the coffee growing area east of Nairobi as far as the Kakusi hills; being most prevalent in the neighbourhoods of Ruiru and Thika. The altitude of infected areas lies as a rule between 5,000 and 5,700 feet; it has however been found on one farm, the altitude of which was as much as 6,500 feet. It appears useless to speculate t See list of references on page 194. 188

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