Impact of water renewal on the residual effect of larvicides in the control of Aedes aegypti.

This study was carried out to evaluate the residual effect of three larvicides under laboratory conditions for 100 days in Aedes aegypti. The larval mortality rate was measured without water renewal or with daily water renewal (80%). With temephos, there was 100% mortality in both groups until the 70th day. In the Bacillus thuringiensis israelensis (Bti)-WDG test, there was no difference during the first 20 days. With Bti-G, without water renewal, mortality was sustained above 90% for up to 35 days. The second experiment (with water renewal) reduced the mortality to below 90% after the first 20 days. When renewed water was provided, the residual effect was significantly lower for all larvicides.

Impact of water renewal on the residual effect of larvicides in the control of Aedes aegypti

This study was carried out to evaluate the residual effect of three larvicides under laboratory conditions for 100 days in Aedes aegypti. The larval mortality rate was measured without water renewal or with daily water renewal (80 percent). With temephos, there was 100 percent mortality in both groups until the 70th day. In the Bacillus thuringiensis israelensis (Bti)-WDG test, there was no difference during the first 20 days. With Bti-G, without water renewal, mortality was sustained above 90 percent for up to 35 days. The second experiment (with water renewal) reduced the mortality to below 90 percent after the first 20 days. When renewed water was provided, the residual effect was significantly lower for all larvicides.

Competência de peixes como predadores de larvas de Aedes aegypti, em condições de laboratório / Efficacy of fish as predators of Aedes aegypti larvae, under laboratory conditions

OBJETIVO: Avaliar a competência de peixes na predação de larvas de Aedes aegypti, em condições de laboratório. MÉTODOS: Foram testados machos e fêmeas de cinco espécies de peixe. Os testes de predação duravam cinco semanas para cada espécie. Cada ensaio compreendia quatro caixas testes e quatro caixas controles. Das caixas controle, duas tinham somente um peixe e as outras duas, apenas larvas. Cada caixa teste continha um peixe e larvas. Na primeira semana foram expostas 100 larvas em cada caixa, e a cada semana acrescentavam-se 100 larvas por caixa/dia, até se obter um máximo de 500 larvas/dia. Comprimento e peso dos peixes foram medidos semanalmente. RESULTADOS: Foram utilizadas 369.000 larvas no total. O Trichogaster trichopteros foi a única espécie em que ambos os sexos predaram 100 por cento das larvas oferecidas. O Betta splendens deixou de predar apenas 15 larvas. Machos do Poecilia reticulata apresentaram baixa capacidade larvófaga quando comparados às fêmeas da mesma espécie. Em relação ao peso e tamanho o Betta splendens mostrou-se capaz de predar 523 larvas/grama/dia. CONCLUSÕES: Fêmeas e machos de Trichogaster trichopteros e de Astyanax fasciatus, e fêmeas de Betta splendens e de Poecillia sphenops foram os peixes que apresentaram maior competência para predar as larvas. Embora com competência menor, machos de Poecillia sphenops e fêmeas de Poecilia reticulata foram capazes de eliminar o número de larvas de Aedes aegypti que possam emergir durante 24 horas num criadouro, em condições naturais. Machos de Poecilia reticulata não foram predadores eficazes.

OBJECTIVE: To evaluate the efficacy of fish as predators of the Aedes aegypti larvae in laboratory conditions. METHODS: The male and female of five different fish were included in the experiment. The tests to measure their consumption ability lasted five weeks for each species. Each trial involved four test tanks and four control tanks. Two control tanks contained just one fish, and the other two just larvae. Each of the test tanks contained one fish and the larvae. During the first week, 100 larvae were placed in the tank, with an additional 100 added every week, up to a maximum daily amount of 500 larvae. The length and weight of the fish were measured at the beginning and end of every week. RESULTS: A total of 369,000 larvae were used. The Trichogaster trichopteros was the only species in which both sexes ate 100 percent of the available larvae. The Betta splendens failed to eat only 15 larvae. The male Poecilia reticulate showed a strong capacity for larvae eating, compared with the female of the same species. In terms of weight and size, the Betta splendens proved capable of eating 523 larvae per gram of weight per day. CONCLUSIONS: The female and male Trichogaster trichopteros and Astyanax fasciatus, and the female Betta splendens and Poecilia sphenops proved to be the most effective predators of the Aedes aegypti larvae. And although the male Poecilia sphenops and female Poecilia reticulata were less effective, they were also capable of eradicating the total number of Aedes aegypti larvae that could appear over 24 hours in a breeding site under natural conditions. The male Poecilia reticulata, however, proved incapable of doing so.

[Efficacy of fish as predators of Aedes aegypti larvae, under laboratory conditions]. / Competência de peixes como predadores de larvas de Aedes aegypti, em condições de laboratório.

OBJECTIVE: To evaluate the efficacy of fish as predators of the Aedes aegypti larvae in laboratory conditions. METHODS: The male and female of five different fish were included in the experiment. The tests to measure their consumption ability lasted five weeks for each species. Each trial involved four test tanks and four control tanks. Two control tanks contained just one fish, and the other two just larvae. Each of the test tanks contained one fish and the larvae. During the first week, 100 larvae were placed in the tank, with an additional 100 added every week, up to a maximum daily amount of 500 larvae. The length and weight of the fish were measured at the beginning and end of every week. RESULTS: A total of 369,000 larvae were used. The Trichogaster trichopteros was the only species in which both sexes ate 100% of the available larvae. The Betta splendens failed to eat only 15 larvae. The male Poecilia reticulate showed a strong capacity for larvae eating, compared with the female of the same species. In terms of weight and size, the Betta splendens proved capable of eating 523 larvae per gram of weight per day. CONCLUSIONS: The female and male Trichogaster trichopteros and Astyanax fasciatus, and the female Betta splendens and Poecilia sphenops proved to be the most effective predators of the Aedes aegypti larvae. And although the male Poecilia sphenops and female Poecilia reticulata were less effective, they were also capable of eradicating the total number of Aedes aegypti larvae that could appear over 24 hours in a breeding site under natural conditions. The male Poecilia reticulata, however, proved incapable of doing so.

[Residual effect of commercial applications of larvicides temefos and Bacillus thuringiensis israelensis on Aedes aegypti larvae in recipients with water renewal]. / Efeito residual de apresentações comerciais dos larvicidas temefos e Bacillus thuringiensis israelensis sobre larvas de Aedes aegypti em recipientes com renovação de água.

The residual effect of temefos (commercial applications A, B and C) and Bacillus thuringiensis israelensis (D and E) on Aedes aegypti larvae was evaluated, in recipients with water renewal. Forty-four beakers of 1,000ml each (8 for each application and 4 controls) were used. In each beaker, 25 larvae were introduced daily. After 24 hours, the dead larvae were counted, the beakers emptied to 200ml and refilled to original volume, with addition of new larvae. The duration of the maximum residual effect (100% of mortality) was: A-19; B-39; C-40; D-8; E-19 days. The mortality ratio of all applications remained equivalent for 25 days; B, C and E maintained MR equivalent up to 45 days; B and C showed MR 2.40 times greater than E, between 46-95 days; B, compared with A, showed MR 1.90-7.51 times greater between 26-95 days. The conclusion was greater effectiveness of two presentations of temefos, even in an epidemiological situation with long exposure to the product and renewal of water in recipients.

Efeito residual de apresentações comerciais dos larvicidas temefos e Bacillus thuringiensis israelensis sobre larvas de Aedes aegypti em recipientes com renovação de água / Residual effect of commercial applications of larvicides temefos and Bacillus thuringiensis israelensis on Aedes aegypti larvae in recipients with water renewal

Avaliou-se o efeito residual do temefos (apresentações comerciais A, B, C) e Bacillus thuringiensis israelensis (D e E) sobre larvas de Aedes aegypti, em recipientes com renovação de água. Utilizaram-se 44 béqueres de 1.000ml (8 para cada apresentação e 4 controles). Em cada béquer introduziram-se diariamente 25 larvas. Após 24 horas, contavam-se as larvas mortas, esvaziavam-se os béqueres até 200ml, repunha-se o volume original e acrescentavam-se novas larvas. A duração do efeito residual máximo (100 por cento de mortalidade) foi: A-19; B-39; C-40; D-8; E-19 dias. A razão de mortalidade permaneceu equivalente entre todos os larvicidas durante 25 dias; B e C mostraram RM 2,40 vezes maior do que E entre 46-95 dias; B, comparado com A, mostrou RM 1,90-7,51 vezes maior entre 26-95 dias. Conclui-se pela maior eficácia de duas apresentações do temefos, mesmo em uma situação epidemiológica de longa exposição ao produto e com renovação de água dos recipientes.