Malaria Control: Efficacy of Bacillus sphaericus 2362 formulations against Anopheles species larvae in man-made breeding sites such as fish culture ponds and brickyard puddles

Abstract

Objective: To evaluate the efficacy and persistence of different formulations of Bacillus
sphaericus 2362, in double dose, as a larvicide of immature forms of Anopheles
species in man-made breeding sites such as fish culture ponds and brickyard puddles
in Manaus and Iranduba, Brazil. Methods: application in a dose twice as large as the
indicated, of Vectolex (22K g/ha), Griselesf (200L/ha) and Spherimos (6L/ha) were
performed at Sítio Fazendinha with 7 ponds and one control (without larvicide); Sítio
Três Irmãos (6 ponds and one control), Sítio Santa Cecília (9 ponds and two controls);
and 26 brickyard puddles with 5 controls in Olaria Cerama. Anopheline breeding sites
samples were collected to calculate the man hour larva index (MHLI); the percentage of reduction was performed in readings on the 2nd, 7th, 14th, 21st, 28th and 35th days
following the application. Results: The results of density of larvae in man-made
breeding sites demonstrated that fish culture ponds had four times more larvae
(33.729) that breeding brickyard puddles (7.972). The efficacy of Bacillus sphaericus
2362 against Anopheles species larvae in man-made breeding sites such as fish culture
ponds presented low larvae indices(MHLI) at the 2nd day reading, they had been
treated with Vectolex and Spherimos in comparison with controls. On the other hand,
when considering the breeding sites were the Griselesf product was applied, similar
larvae indices(MHLI) and controls were obtained at all readings. The percentage of
reduction with Spherimos and Vectolex were nearly 100% at the 2nd day observation,
for mature and young larvae. The Griselesf product presented lower reduction in fish
culture ponds (55%). At the Cerama brickyard, the lowest larvae index averages were
found in the breeding sites where the Vectolex larvicide was applied when considering
the most mature larvae (3rd and 4th instars). The limnological analyses demonstrated a large amount of organic matter in the breeding sites, which would require lower toxicity, nonetheless, the results were positive, i.e., the tanks remained with no anopheline larvae. Conclusions: In man-made breeding sites such as fish culture ponds and brickyard puddle there are favourable conditions for the development of Anopheles species. The application of double doses than recommended of Spherimos and Vectolex were effective against Anopheles species, while in brickyard puddle these doses were less effective. In order to control Anopheles larvae in fish culture ponds under the conditions found in the Amazon, we conclude that the first option is Spherimos, followed by Vectolex and Griselesf as second and third options.