In the area selected for this investigation, which included two scattered communities in the cocoa growing districts of Tamana Reserve, four species of Anopheles were found: A. bellator, A. oswaldoi, A. mediopunctatus, and A. nimbus. A. mediopunctatus and A. nimbus were rare and A. oswaldoi could be collected with regularity, but none of these species is abundant enough, under present conditions, to be involved in the transmission of malaria in this highly malarious area of Trinidad. A. bellator, the predominant species, was present in great numbers.
A. bellator attacked man viciously, literally swarming about people during the hours when the females became active. Although attracted to cows and donkeys, it seemed to prefer the blood of man to that of animals. A. oswaldoi fed readily on man, but appeared to be associated primarily with animals, especially cattle.
A. bellator will attack man throughout the afternoon, especially on dark days and in the shade of the forest, but the real flight begins at about 5:30 p.m., and continues until about 8:00 p.m., with the peak occurring between 6:30 and 7:00 p.m. The species becomes active early in the morning also, between four and six-thirty o'clock, but the morning flight is light as compared with the evening flight.
A. bellator will feed on man both indoors and out of doors. It will enter houses, and even bed nets, in search of human blood, but it attacks more readily out of doors or under the roofs of cocoa-drying or similar sheds without walls. The females do not remain in houses after feeding, but return immediately to their jungle resting places.
The larvae of A. bellator were found only in Bromeliaceae, and of four species of bromeliads examined, the larvae were collected from two: a species of Wittmackia, and one of Gravisia. Gravisia is the chief A. bellator producing bromeliad in Trinidad.
Experimental infections of A. bellator were obtained twice, and proved that the species is very susceptible to at least one of the species of Plasmodium causing human malaria. Oöcysts were found in two of four A. oswaldoi that fed on a P. vivax gametocyte carrier.
Three of 725 “wild” A. bellator were found to be naturally infected with Plasmodium; one had a single mature oöcyst on the stomach wall, another had infected salivary glands, and the third had nine small oöcysts on the stomach wall.
The evidence presented confirms the conclusion of De Verteuil, that A. bellator is the vector of malaria in the interior cocoa growing districts of Trinidad.
From the Health Service, Caribbean Division, Corps of Engineers, U. S. Army, and the Division of Medical Entomology, School of Hygiene and Public Health, the Johns Hopkins University. The authors are indebted to Lieut. Col. L. A. Fox for making possible this investigation, and for his aid in outlining the problem. They also wish to thank Dr. Eric de Verteuil for his interest and cooperation in this work.