Competência de peixes como predadores de larvas de Aedes aegypti, em condições de laboratório

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Abstract

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% 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.

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Resistance of Aedes aegypti to organophosphates in several municipalities in the State of Rio de Janeiro and Espírito Santo, Brazil.

Francisco J B Lima, Mônica R. O. G. C. M. Silva, I Braga Goncalves … (2003)

Chemical insecticides have been widely used in Brazil for several years. This exposes mosquito populations to an intense selection pressure for resistance to insecticides. In 1999, the Brazilian National Health Foundation started the first program designed to monitor the resistance of Aedes aegypti to insecticides. We analyzed populations from 10 municipalities (from 84 selected in Brazil) in the states of Rio de Janeiro and Espírito Santo. Exposure of larvae to a diagnostic dose of temephos showed in alterations in susceptibility in all populations. Mosquitoes from eight municipalities exhibited resistance, with mortality levels ranging from 74% (Campos dos Goytacazes, Rio de Janeiro) to 23.5% (São Gonçalo, Rio de Janeiro). The resistance ratios of mosquitoes from three municipalities ranged from 3.59 to 12.41. Adults from only one municipality (Nova Iguaçu, Rio de Janeiro) remained susceptible to both fenitrothion and malathion. These results are being used to define new local vector control strategies.

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Oviposition attraction and repellency of Aedes aegypti (Diptera: Culicidae) to waters from conspecific larvae subjected to crowding, confinement, starvation, or infection.

Bettina M. Rau, N Zahiri (1998)

As the biomass of Aedes aegypti (L.) larvae increased in relation to the volume of rearing waters, oviposition attraction of these waters to conspecific, gravid females first rose to a peak and then declined. Further increases in biomass rendered waters strongly repellent. Comparable responses were elicited by a decrease in the volume of rearing waters or an increase in the relative size or number of mosquito larvae. Low volumes of water reduced oviposition attraction and increased repellency, whereas larger volumes increased attraction. Excessively large volumes diluted attraction to neutrality. Constraints imposed by the physical dimensions of the larval environment which interfered with the normal postural movements and behaviors of the larvae also induced repellency, independent of rearing volume. Titration of repellent waters revealed that infection with the digenean Plagiorchis elegans (Rudolphi) generated the most powerful repellent effect, whereas crowding or starvation induced significantly weaker responses. At no time did dilution of repellent waters restore attractive properties. Repellents, even at minute concentrations, overrode attractants. The density-dependent action of oviposition attractants and repellents may help to maintain larval populations near optimal levels through their influence on recruitment. Oviposition repellency induced by sublethal infections with P. elegans may maintain population levels below the carrying capacity of the environment. Persistence of oviposition attraction and repellency varied inversely with temperature. The magnitude of the repellent effect induced by larvae appears to be a good indicator of their probability of survival and may be of selective significance. Repellency may deflect ovipositing females away from sites close to human habitation and may lead to new, and perhaps more effective, method, to control mosquitoes and the diseases they transmit.