Hybrid sterility in crosses between two Brazilian sibling species of the Anopheles albitarsis complex.

BACKGROUND: Complexes of cryptic species are common in several taxa and this is also the case in the Anopheles genus, a group including all known human malaria vectors. The Anopheles albitarsis complex comprises at least nine cryptic species, some of which are implicated as vectors of human malaria. Several different types of data have been generated for this species complex such as cytogenetics, alloenzymes, morphological and feeding behavioral, hybridization experiments, RAPD-PCR and RFLP and mitochondrial and nuclear markers. Studies focused on its postzygotic isolation are still somewhat rare in the literature despite their importance to understand the speciation process and the level of gene flow potentially occurring among the different sibling species. METHODS: Hybridization experiments between Anopheles albitarsis s.s. and Anopheles marajoara, as well as backcrosses between hybrids and Anopheles albitarsis s.s., were performed using the induced mating technique. Results were compared to intraspecific crosses. Larva-to-adult viability and sex ratio were also assessed. RESULTS: Male hybrids show very low insemination rates and nearly complete sterility, apparently due to abnormalities in their reproductive organs. Evidence of partial sterility among the hybrid females was also observed. CONCLUSIONS: Our data indicated that Anopheles albitarsis s.s. and Anopheles marajoara show a high level of postzygotic isolation with a strong hybrid male sterility. This result is consistent with the Haldane's rule which states that in interspecific crosses the heterogametic sex is the first to be affected. However, the fact that the females are not completely sterile raises the possibility of introgression between these two siblings species.

The efficacy of a chitin synthesis inhibitor against field populations of organophosphate-resistant Aedes aegypti in Brazil

The mosquito Aedes aegypti is the main focus of dengue control campaigns. Because of widespread resistance against conventional chemical insecticides, chitin synthesis inhibitors (CSIs) are considered control alternatives. We evaluated the resistance status of four Brazilian Ae. aegypti populations to both the organophosphate temephos and the pyrethroid deltamethrin, which are used in Brazil to control larvae and adults, respectively. All vector populations exhibited high levels of temephos resistance and varying rates of alterations in their susceptibility to pyrethroids. The effect of the CSI novaluron on these populations was also investigated. Novaluron was effective against all populations under laboratory conditions. Field-simulated assays with partial water replacement were conducted to evaluate novaluron persistence. Bioassays were continued until an adult emergence inhibition of at least 70% was attained. We found a residual effect of eight weeks under indoor conditions and novaluron persisted for five-six weeks in assays conducted in an external area. Our data show that novaluron is effective against the Ae. aegypti populations tested, regardless of their resistance to conventional chemical insecticides.

The efficacy of a chitin synthesis inhibitor against field populations of organophosphate-resistant Aedes aegypti in Brazil.

The mosquito Aedes aegypti is the main focus of dengue control campaigns. Because of widespread resistance against conventional chemical insecticides, chitin synthesis inhibitors (CSIs) are considered control alternatives. We evaluated the resistance status of four Brazilian Ae. aegypti populations to both the organophosphate temephos and the pyrethroid deltamethrin, which are used in Brazil to control larvae and adults, respectively. All vector populations exhibited high levels of temephos resistance and varying rates of alterations in their susceptibility to pyrethroids. The effect of the CSI novaluron on these populations was also investigated. Novaluron was effective against all populations under laboratory conditions. Field-simulated assays with partial water replacement were conducted to evaluate novaluron persistence. Bioassays were continued until an adult emergence inhibition of at least 70% was attained. We found a residual effect of eight weeks under indoor conditions and novaluron persisted for five-six weeks in assays conducted in an external area. Our data show that novaluron is effective against the Ae. aegypti populations tested, regardless of their resistance to conventional chemical insecticides.

Efeito do Novaluron - um inibidor da síntese de quitina - sobre Aedes aegypti em laboratório e simulado de campo / Effect of the Novaluron - an inhibitor of the chitin synthesis - on Aedes aegypti in simulated laboratory and of field

A dengue é um grande problema de saúde pública. Esta arbovirose é transmitida por mosquitos do gênero Aedes, sendo o principal vetor o Aedes aegypti. Ainda hoje o alvo principal das campanhas de controle dessa doença é o vetor e, dentre as possibilidades, o controle químico é ainda mais comum. Atualmente para o controle de aedes aegypti no Brasil são utilizados principalmente os larvicidas temephos e Bti e o adulticida deltametrina. Detectamos por meio de ensaios tipo dose-resposta, resistência a temephos nas quatro populações avaliadas - Cuiabá, MT, Uberaba, MG, Aracajú, SE e Henrique Jorge/Fortaleza, CE. Henrique Jorge foi notadamente a população com maior alteração na resposta a temephos. Por outro lado, somente Cuiabá se mostrou sensível a deltametrina, enquanto as outras populações apresentaram resistência incipiente. Com o aumento da resistência aos inseticidas químicos usados, novas alternativas de controle, se fazem necessárias. Dentre estas se encontram os inibidores de síntase de quitina (CSI). O novaluron é um inibidor da síntese de quitina e foi recentemente recomendado pela OMS para uso em água potável, o que o qualifica como uma alternativa viável ao controle de larvas do vetor de dengue. Em condições de laboratório novaluron apresentou grande eficácia sobre larvas de Aedes aegypti da cepa Rockefeller: total inibição da emergência de adultos viáveis desta cepa foi obtida com a concentração 0,4(miu)g/L. Novaluron também se mostrou eficaz sobre as populações do campo testadas e nenhuma delas apresentou resistência a este CSI, independente de seu status de resistência aos inseticidas químicos avaliados. Em simulado de campo, foram avaliadas a cepa Rockefeller e as populações Aracajú e Henrique Jorge. Com a concentração 20(miu)g/L, o produto mostrou boa persistência em área externa e interna sobre larvas de Aedes aegypti. Em área externa, no período de março a maio, mortalidade acima de 70por cento foi obtida até a sexta semana, enquanto...químicos.