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Dispersion of Forest Mosquitoes in Brazil: Further Studies¹

Further studies of the dispersion of sylvan mosquitoes marked with bronzing powders confirm and extend the observations previously reported. Using the same technique, but searching over a wider area, Haemagogus spegazzinii, perhaps the most important transmitter of jungle yellow fever in Brazil, was recaptured as far as 11.5 kilometers from the point of release, and Aedes leucocelaenus, another efficient vector, was recovered up to 5.7 kilometers away. Out of a total of 7,624 marked H. spegazzinii released, 98 or 1.3 per cent, were recaptured. Other species of mosquitoes recovered at long distances were A. serratus at 11.5 kilometers, Psorophora ferox at 10.8 kilometers, Wyeomyia sp. at 5.7 kilometers, A. terrens at 5.6 kilometers, and Chagasia sp. at 2.3 kilometers. The longest survival so far recorded is that of P. ferox, a specimen of which was found 55 days after release. In view of these findings, it seems logical to suspect that yellow fever virus may be disseminated by the movement of insect vectors in regions of small residual forests, surrounded by open pasture land and cultivated fields, as typified by the country in western Minas Gerais.

An additional series of experiments to determine the influence of wind on this movement showed that forest mosquitoes travel in the directions of the prevailing winds during the hours of daylight. On no occasion was a marked specimen recaptured in a forest which could have been reached only by flight against the wind.

¹ The work on which these observations are based was carried out under the auspices of the Serviço de Estudos e Pesquisas sôbre a Febre Amarela, which is maintained jointly by the Ministry of Education and Health of Brazil and the International Health Division of The Rockefeller Foundation.