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Contributo para o estudo bioecológico de Culex (Culex) theileri Theobald, 1903 e Ochlerotatus (Ochlerotatus) caspis (Pallas, 1771) (Diptera: Culicidae) na áre da Comporta, Alcácer do Sal. Perspectivas para o seu controlo.
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Culex theileri e Ochlerotatus caspius (Diptera: Culicidae) são duas espécies de mosquitos reconhecidamente abundantes em Portugal. Embora consideradas espécies zoofílicas, devido ao seu comportamento oportunista, mais marcado em Oc. caspius, representam fonte de incomodidade nas suas áreas de distribuição e durante os períodos de maiores densidades populacionais. Além disso são ainda vectores de agentes patogénicos com importância médica e/ou veterinária.
Este estudo teve como objectivos o levantamento destas espécies a nível do território de Portugal continental e o estudo da sua bioecologia na área da Comporta, Alcácer do Sal, distrito de Setúbal, bem como das perspectivas para o seu controlo usando o bioinsecticida Bacillus thuringiensis var. israelensis (Bti).
As prospecções efectuadas durante este estudo permitiram confirmar a maior densidade de Cx. theileri no centro-sul do País e a distribuição costeira de Oc. caspius, apresentando-se estas espécies como as mais abundantes a seguir a Cx. pipiens.
Na área da Herdade da Comporta, Alcácer do Sal, pelo contrário, Cx. theileri e Oc. caspius são quase sempre, respectivamente, a primeira e segunda espécies mais abundantes. São ainda as que mais picam o Homem, respectivamente 300 e 200 picadas por hora e Homem. Apresentam ainda ciclos diários de actividade que se complementam, tendo Oc. caspius dois picos de actividade, nos crepúsculos matutino e vespertino, e Cx. theileri mantendo níveis elevados de actividade ao longo da noite. Observou-se que Cx. theileri e Oc. caspius são mais adequadamente amostradas com armadilhas CDC/CO2, apresentando picos de abundância, mais alargados para Cx. theileri, durante os meses de Abril a Outubro.
Na região de estudo, larvas de Cx. theileri podem ser encontradas nos arrozais e ainda em algumas valas associadas a actividade agrícola. Ochlerotatus caspius utiliza como biótopos larvares não só as depressões existentes no sapal que apenas são alagadas pelas marés vivas e água das chuvas, mas também os arrozais da região após a sua segunda inundação. Culex theileri está presente nos arrozais em todas as localidades positivas para culicídeos, o mesmo não se podendo dizer de Oc. caspius que, para além do sapal, foi identificado nos arrozais do Cambado, Possanco e Torre, não se registando no Carvalhal, sempre no início da campanha de cultivo do arroz, após a primeira drenagem, com a segunda inundação. Quanto às outras espécies, pelo contrário, pareceexistir uma tendência para serem encontradas já na fase final do ciclo de produção dos arrozais, quando é mais marcada a eutrofização das águas. Durante este estudo, nem Cx. theileri nem Oc. caspius foram encontrados a colonizar tanques, recipientes de armazenamento de água e bebedouros de animais.
Na caracterização fisico-química da água dos biótopos potenciais prospectados encontrou-se menor teor de oxigénio dissolvido nos biótopos positivos para culicídeos em relação aos negativos. Não se registaram diferenças nos parâmetros da água dos biótopos de Cx. theileri, apresentando os biótopos de Oc. caspius pH, condutância específica, total de sólidos dissolvidos, salinidade e oxigénio dissolvido superiores, e potencial redox inferior, em relação aos dos biótopos larvares onde não estava presente.
De um modo geral, ambas as espécies se encontram simultaneamente nas formas imaturas e adultas em todos os locais amostrados.
Apresentando estas espécies um comportamento exofílico, uma das abordagens mais adequada para o controlo das suas populações será constituída por técnicas de redução das densidades larvares. Assim, procedeu-se à realização de ensaios de campo em pequena escala com o larvicida Bti em suspensão aquosa, tendo-se obtido percentagens significativas de redução da densidade larvar total 24h após o tratamento, sempre superiores a 85%. As densidades larvares totais apresentaram contudo uma franca recuperação durante a semana seguinte ao tratamento, facto que pensamos dever--se à reduzida dimensão e não isolamento da área tratada.
Foi também determinada a sensibilidade de Cx. theileri de insectário à mesma formulação de Bti aplicada nos ensaios de campo, tendo-se calculado os valores 154,0 μg/l e 332,5 μg/l para a LD50 e LD90, respectivamente. Foi ainda possível avaliar o impacte do larvicida na duração do desenvolvimento dos indivíduos sobreviventes à exposição ao Bti durante 24h.
A aplicação de Bti na área de estudo, parece apresentar-se então como uma das medidas a adoptar no controlo da incomodidade causada por estas espécies.
Culex theileri and Ochlerotatus caspius (Diptera: Culicidae) are recognised as two of the most abundant species of mosquitoes in Portugal. These species are considered zoophilic. However, due to their markedly opportunistic biting behaviour, particularly evident in Oc. caspius, they are an important source of nuisance to humans along their distribution areas and during high density periods. In addition, both species are vectors of pathogens of both medical and veterinary importance. This study aimed at surveying these species in Portugal mainland, studying their bioecoly in the area of Comporta, Alcácer do Sal, district of Setúbal, as well as the perspectives for their control, using the bioinsecticide Bacillus thuringiensis var. israelensis (Bti). Country-wide surveys conducted in this study confirmed a higher density of Cx. theileri in the south-central region of Portugal and a coastal distribution for Oc. caspius. After Cx. pipiens, these were the most abundant mosquitoes in the country. However, in Herdade da Comporta, Alcácer do Sal, Cx. theileri and Oc. caspius were the first and the second most abundant species recorded. They were also the major human-biting mosquitoes with 300 and 200 bites per hour and per person, respectively. These species present complementary daily biting cycles, Oc. caspius has two biting peaks, in the morning and evening twilights, and Cx. theileri maintains high levels of activity through the night. We observed that Cx. theileri and Oc. caspius are more adequately sampled with CDC/CO2 traps, presenting peaks of abundance from April to October, wider for Cx. theileri. In the region studied, Cx. theileri larvae can be found in rice-fields and in ditches associated with agricultural activities. Ochlerotatus caspius explores small pools of brackish water in marshlands that are flooded by the large tides or by rainfall. Larvae of this species can also be found in rice fields particularly after their second flooding. Culex theileri is present in rice fields in all the localities positive for culicids, while Oc. caspius, was found in the marshland and was found in rice paddies of Cambado, Possanco and Torre, but not in Carvalhal, always at the beginning of the rice farming campaigns, after the first draining, with the second flooding. As for the other species, there is a tendency for their appearance towards the end of rice growing cycle, when the eutrophication of water is higher. During this study, neither Cx. theileri nor Oc. caspiuswere ever found in water tanks, water storage containers and animal drinking containers. In what concerns the physical and chemical characterization of the potencial biotopes water, a lesser amount of dissolved oxygen was found in the biotopes positive for culicids as opposed to the negative. No diferences were registered in the parameters of the biotopes positive for Cx. theileri, while the biotopes positive for Oc. caspius had higher pH, specific conductance, total dissolved solids, salinity and dissolved oxygen, and lower redox potential, in relation to the biotopes where this species was absent. Generally, both species were found simultaneously in the immature and adult forms in all the localities sampled. Since Cx. theileri and Oc. caspius are markedly exophilic, one of the most adequate approaches for control of their populations, should be aimed at larval reduction. Thus, small-scale field experiments with the larvicide Bti in aqueous suspension were carried out. Significant reductions, always above 85%, in total larval densities were obtained 24 h after treatment. However, larval densities increased to pre-treatment levels one week after Bti application. This could be explained by the relatively small area treated and by its lack of isolation from untreated areas. The susceptibility of Culex theileri from an insectary colony to the same formulation of Bti was determined in the laboratory with estimation of Lethal Dosages 50 and 90, as 154,0 μg/l and 332,5 μg/l for LD50 and LD90, respectively. The effect of the insecticide in the larval development of survivors that were exposed to Bti for 24h was also evaluated. In conclusion, the application of Bti can be considered as a measure to be adopted for the control of mosquito nuisance in the study area.
Culex theileri and Ochlerotatus caspius (Diptera: Culicidae) are recognised as two of the most abundant species of mosquitoes in Portugal. These species are considered zoophilic. However, due to their markedly opportunistic biting behaviour, particularly evident in Oc. caspius, they are an important source of nuisance to humans along their distribution areas and during high density periods. In addition, both species are vectors of pathogens of both medical and veterinary importance. This study aimed at surveying these species in Portugal mainland, studying their bioecoly in the area of Comporta, Alcácer do Sal, district of Setúbal, as well as the perspectives for their control, using the bioinsecticide Bacillus thuringiensis var. israelensis (Bti). Country-wide surveys conducted in this study confirmed a higher density of Cx. theileri in the south-central region of Portugal and a coastal distribution for Oc. caspius. After Cx. pipiens, these were the most abundant mosquitoes in the country. However, in Herdade da Comporta, Alcácer do Sal, Cx. theileri and Oc. caspius were the first and the second most abundant species recorded. They were also the major human-biting mosquitoes with 300 and 200 bites per hour and per person, respectively. These species present complementary daily biting cycles, Oc. caspius has two biting peaks, in the morning and evening twilights, and Cx. theileri maintains high levels of activity through the night. We observed that Cx. theileri and Oc. caspius are more adequately sampled with CDC/CO2 traps, presenting peaks of abundance from April to October, wider for Cx. theileri. In the region studied, Cx. theileri larvae can be found in rice-fields and in ditches associated with agricultural activities. Ochlerotatus caspius explores small pools of brackish water in marshlands that are flooded by the large tides or by rainfall. Larvae of this species can also be found in rice fields particularly after their second flooding. Culex theileri is present in rice fields in all the localities positive for culicids, while Oc. caspius, was found in the marshland and was found in rice paddies of Cambado, Possanco and Torre, but not in Carvalhal, always at the beginning of the rice farming campaigns, after the first draining, with the second flooding. As for the other species, there is a tendency for their appearance towards the end of rice growing cycle, when the eutrophication of water is higher. During this study, neither Cx. theileri nor Oc. caspiuswere ever found in water tanks, water storage containers and animal drinking containers. In what concerns the physical and chemical characterization of the potencial biotopes water, a lesser amount of dissolved oxygen was found in the biotopes positive for culicids as opposed to the negative. No diferences were registered in the parameters of the biotopes positive for Cx. theileri, while the biotopes positive for Oc. caspius had higher pH, specific conductance, total dissolved solids, salinity and dissolved oxygen, and lower redox potential, in relation to the biotopes where this species was absent. Generally, both species were found simultaneously in the immature and adult forms in all the localities sampled. Since Cx. theileri and Oc. caspius are markedly exophilic, one of the most adequate approaches for control of their populations, should be aimed at larval reduction. Thus, small-scale field experiments with the larvicide Bti in aqueous suspension were carried out. Significant reductions, always above 85%, in total larval densities were obtained 24 h after treatment. However, larval densities increased to pre-treatment levels one week after Bti application. This could be explained by the relatively small area treated and by its lack of isolation from untreated areas. The susceptibility of Culex theileri from an insectary colony to the same formulation of Bti was determined in the laboratory with estimation of Lethal Dosages 50 and 90, as 154,0 μg/l and 332,5 μg/l for LD50 and LD90, respectively. The effect of the insecticide in the larval development of survivors that were exposed to Bti for 24h was also evaluated. In conclusion, the application of Bti can be considered as a measure to be adopted for the control of mosquito nuisance in the study area.
Descrição
Palavras-chave
Parasitologia médica Vectores Culex theileri Ochlerotatus caspius Entomologia Culicideos
Contexto Educativo
Citação
Editora
Instituto de Higiene e Medicina Tropical