Bromeliad Malaria in Trinidad, British West Indies

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  • Malaria Laboratory, Trinidad, British West Indies

Summary

Lutz (1903) first considered the possibility that anopheline mosquitoes of the subgenus Kerteszia might be involved in malaria transmission. He concluded, on epidemiological grounds, that Anopheles lutzi Theobald (= cruzi D. & K.) was a vector in São Paulo. However, Knab, stressing the connection between the feeding habits of insects and their importance as vectors of disease strongly opposed Lutz's view, maintaining that since Anopheles lutzi was a forest mosquito it would not have sufficient contact with man to transmit malaria.

Independently, Urich and later de Verteuil believed that Anopheles (Kerteszia) bellator D. & K. was involved in the malaria complex in Trinidad, and this was confirmed eventually by Rozeboom and Laird, and also by Downs, Gillette, and Shannon.

It is shown that in spite of the fact that Anopheles bellator is a forest mosquito it is intimately associated with man in the cacao areas of Trinidad. Two principal factors are adduced to account for this contact: in the first place Anopheles bellator inhabits the drier microclimates of the forest and is therefore able to leave forest as such for the drier conditions offered by cacao estates and the open spaces in the villages; secondly, the cacao industry has brought relatively large human settlements into immediate contact with the forests of cacao and immortelle trees, which support both larval and adult populations of A. bellator and heavy growths of water-holding bromeliads in which the anophelines breed.

The breeding of A. bellator is restricted to certain bromeliad species. Its absence in some very common species such as Aechmea nudicaulis is a fact of practical importance. Again, bellator does not occur all over the island where forests and cacao estates exist. It is restricted to areas of high rainfall.

In discussing control problems the writers do not consider that the simple removal of plants by hand could ever be adopted as a regular control procedure. It is too slow, expensive, and dangerous.

It is shown that copper sulphate may be used as a selective herbicidal spray to destroy the bromeliad infestations without damaging the commercially important cacao trees or the immortelles. In field practice the heavy spraying equipment developed by the United States Department of Agriculture for the control of the gypsy moth is found to be highly satisfactory. This control method is much faster, cheaper, and safer than removal of bromeliads by hand.

Finally it is pointed out that a change in agricultural practice, namely, the abandonment of interplanted immortelle shade trees and the adoption of windbreaks, would remove the ecological basis of the disease, which is the microclimatic condition produced by immortelle trees in existing cacao estates. Following such a change, which is now being encouraged by the Government of Trinidad and Tobago, endemic bromeliad malaria could be expected to disappear from the center of the island.

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