Observations on mosquito activity in primitive rain forests on plains, and epidemiological profiles for several environments in the Ribeira Valley, S.Paulo, Brazil

Abstract

Monthly 25-hour catches of Culicidae mosquitoes were carried out at ground level with human bait, in two primitive rain forests on plains in the Ribeira Valley, S.Paulo, Brazil. Regular simultaneous catches were made too, with Shannon traps, both within and outside wooded environments, which included quaternary and transitional forests on plains. Results obtained are presented and discussed. The An. cruzii dominance, though present, was not so remarkable as in the highland forest, previously reported on another work (1986). Nevertheless this mosquito, together with Ae. serratus and An. bellator, showed uninterrupted daily activity with regard to human bait, but with a marked increase at night for the two Kerteszia species. Both these anophelines showed a very clear peak of biting activity at the dusk crepuscular period, sustained in a significant manner outside the forest environments. At the dawn crepuscular period these two mosquitoes showed a peak too. For both crepuscular periods the occurrence of paracrepuscular rhythms including a secondary peak which immediately follows, was confirmed at the two investigation sites. Day-time activity was shown by Sabetini and Ps. ferox, while a nocturnal one was markedly shown by Cx. sacchettae with a clear eocrepuscular rhythm. Even though Ae. scapularis was not a dominant species within the forest, it was collected in significant quantity with the Shannon trap outside the quaternary forest on the plain, while Ae. serratus was found only inside woods. These results allow a comparison with others previously published in 1981 and 1986 and obtained in different Ribeira Valley environments. So it has been possible to describe culicid fauna profiles for three primitive forests, that is to say one on the highland and two on the plain, beside the patch one remaining as extensively modified land for agricultural purposes. The results showed a culicid faunistic succession where the former dominance of An. cruzii, Cx. sacchettae, An. bellator and Ps. ferox in the primitive forest environments was replaced by that of Ae. serratus, Ae. scapularis and Cx. ribeirensis. Besides this, only the two last of these were collected outside a forest environment on the modified land. So this finding allows one to draw conclusions as to the epidemiological importance of An. cruzii in primitive environments and of Ae. scapularis and Cx. ribeirensis in modified ones.