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 1V. Reduviid bug, Rhinocoris tibialis, St., preys on adult Chilocorus lady- birds, and may at times work serious havoc among them, while a smaller bug of the same family, Ploiariodes sp., appears to specialize on the Psocids. But the real enemy of all, or at any rate of all the commoner predaceous insects, is a small Myrmecine ant, Pheidole punctulata, Meyr. This ant attends the coffee mealy-bug for .the sake of its sweet secretion. In so doing it in some way favours the growth of the mealy-bug—whether the actual attention of the ants is beneficial, or whether there is merely less mortality among the mealy-bug when the ants are present to act, as they do, as scavengers, is not quite certain. In any case, when kept in the laboratory completely protected from all natural enemies, the mealy-bug multiplies much faster in the presence of this ant. Again, this ant attacks and destroys most of, and possibly all, the beneficial predatory insects. It is at any rate known to kill the adults of Chilocorus and almost certainly their eggs, the adults of both species of Hyperaspis and the larve of Scymnus sp.; the larvae of Chrysopa sp., and the three commoner species of Psocids. Tt also destroys both adults and larve of the imported lady-bird Crypotolemus montrouzieri. Pheidole punctulata appears to be distributed over the greater part of the area where the common coffee mealy-bug is found, except that it is not yet known to occur west of the Karura river, and in this locality the mealy-bug, though it occurs sporadically, does not appear to assume the proportions of a major pest. It is here attended by a Camponotine ant which is presumably not so destructive as Pheidole to the predatory insects, and these always seem to be able to deal with an attack of mealy-bug by themselves. But where Pheidole occurs, such unaided natural control is impossible, as the ant breeds faster and increases with the presence of its favourite food, and the mealy-bug increases with the presence of the ant. It therefore appeared, and was subsequenty abundantly proved by experiments, that if the ants were denied access to an infected coffee tree, the mealy-bug would rapidly be destroyed by its enemies. Actually, under favourable conditions, almost complete ‘eradication of the mealy-bug is affected in about five weeks, though on some plantations, from causes which are at present obscure, a much longer time is taken. - There can however be no doubt but that this procedure of encouraging the already existing enemies of the mealy-bug is the most effective method at present known of combating this pest. The only alternative is spraying, and no spray can be expected to reach quite all the mealy-bugs on a coffee tree; while it will kill many of the predators and drive away the majority of the remainder. In point of fact, there are coffee plantations in this country which were sprayed, and though a temporary benefit was obtained, subsequently became infected worse than before. ~~ The actual method of keeping the ants away from the mealy-bug 1S.a more difficult matter. Poison baits, such as have proved Successful against the Argentine Ant (9, p. 12) and several others have been tried without success, as these ants learn by experience that the bait is poisonous, and once a few workers have been killed, refuse to * See list of references on page 194. 195

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