Spatial and temporal country-wide survey of temephos resistance in Brazilian populations of Aedes aegypti

The organophosphate temephos has been the main insecticide used against larvae of the dengue and yellow fever mosquito (Aedes aegypti) in Brazil since the mid-1980s. Reports of resistance date back to 1995; however, no systematic reports of widespread temephos resistance have occurred to date. As resistance investigation is paramount for strategic decision-making by health officials, our objective here was to investigate the spatial and temporal spread of temephos resistance in Ae. aegypti in Brazil for the last 12 years using discriminating temephos concentrations and the bioassay protocols of the World Health Organization. The mortality results obtained were subjected to spatial analysis for distance interpolation using semi-variance models to generate maps that depict the spread of temephos resistance in Brazil since 1999. The problem has been expanding. Since 2002-2003, approximately half the country has exhibited mosquito populations resistant to temephos. The frequency of temephos resistance and, likely, control failures, which start when the insecticide mortality level drops below 80%, has increased even further since 2004. Few parts of Brazil are able to achieve the target 80% efficacy threshold by 2010/2011, resulting in a significant risk of control failure by temephos in most of the country. The widespread resistance to temephos in Brazilian Ae. aegypti populations greatly compromise effective mosquito control efforts using this insecticide and indicates the urgent need to identify alternative insecticides aided by the preventive elimination of potential mosquito breeding sites.

Atividade inseticida in vitro do óleo de sementes de nim sobre Lutzomyia longipalpis (Diptera: Psychodidae) / In vitro insecticidal activity of seed neem oil on Lutzomyia longipalpis (Diptera: Psychodidae)

Lutzomyia longipalpis é o principal vetor da Leishmaniose visceral no Brasil. O objetivo deste trabalho foi avaliar o efeito do óleo de sementes de nim (Azadirachta indica) sobre ovos, larvas e adultos do vetor. Os insetos foram capturados no campo e mantidos no laboratório a ± 27 °C e 80 por cento de umidade relativa. Cinco tratamentos com diferentes concentrações foram realizados, usando-se dois controles negativos, um com água destilada e outro com Tween 80 (3 por cento) e um controle positivo com cipermetrina. Os ovos foram borrifados com o óleo em diferentes concentrações e avaliou-se o número de larvas eclodidas por 10 dias consecutivos. A mortalidade das larvas foi observada até a pupação, e a mortalidade dos adultos foi observada após 24, 48, e 72 horas. A análise estatística foi feita pelo teste de Tukey a 5 por cento de probabilidade. No teste com ovos, a maior concentração obteve 65,16 ± 3,24 por cento de eficácia. O teste com larvas apresentou 67,75 ± 2,21 por cento de eficácia na concentração de 100 mg.mL-1. Com adultos, a eficácia na concentração de 100 mg.mL-1 foi de 96,64 ± 4,11 por cento, após 24 horas. A análise fitoquímica revelou a presença de triterpenos. Esses resultados demonstram o potencial uso desse óleo no controle deste vetor.

Lutzomyia longipalpis is the main vector of visceral leishmaniasis in Brazil. The objective was to evaluate the effect of oil from (Azadirachta indica) neem seeds on eggs, larvae and adults of the vector. The insects were captured in the field and kept in the laboratory at ± 27 °C and 80 percent relative humidity. Five treatments with different concentrations were performed using two negative controls (distilled water and Tween 80) and a positive control. The eggs were sprayed with the oil at different concentrations and the number of hatched larvae evaluated for 10 days. Mortality of larvae was observed to pupation and adult mortality was observed after 24, 48, and 72 hours. Statistical analysis was performed by Tukey test at 5 percent probability. The highest oil concentration of eggs obtained 65.16 ± 3.24 percent efficacy for reducing egg hatching. The test with larvae showed 67.75 ± 2.21 percent efficacy at a concentration of 100 mg.mL-1. In adults, the efficacy of the 100 mg.mL-1 concentration was 96.64 ± 4.11 percent after 24 hours. The phytochemical analysis revealed the presence of triterpenes. These results demonstrate the potential use of this oil in the control of this vector.