Resistance of Brazilian diamondback moth populations to insecticides

Plutella xylostella is a recurring pest on cruciferous crops around the world. In Brazil, it typically requires large number of insecticide sprays, which may lead to fast evolution of resistance. The aim of this study was to assess the susceptibility of Brazilian diamondback moth populations to the insecticides abamectin, deltamethrin, and spinosad. Leaf dip bioassays were used to determine mortality data obtained after 48 h of exposure to insecticides and subjected to Probit analysis. The population from Bonito, state of Pernambuco, Brazil, had the highest toxicity ratio (20.2 - fold) to abamectin compared to the reference population. The LC50 values for deltamethrin ranged from 85.2 to 360.1 mg L-1, demonstrating a high survival of populations in relation to this insecticide field dose rate (7.5 mg L-1). The toxicity ratios of the estimated LC50s, however, were very low (varying from 2.2 - to 4.2 - fold). Most populations exhibited toxicity ratios for spinosad, ranging from 2.3 - to 5.1 - fold, while both the LC50 and LC95 values reflected a high susceptibility to the spinosad field dosage (120 mg L-1). Only the Bonito - PE population resisted to abamectin, while all P. xylostella populations were resistant to deltamethrin, but particularly susceptible to spinosad because of the absence of selection pressure with it in these areas.Plutella xylostella é uma praga recorrente em brássicas de todo o mundo. No Brasil, normalmente exige grande número de pulverizações de inseticidas, que pode levar à rápida evolução da resistência. Avaliou-se a suscetibilidade de populações brasileiras da traça das crucíferas aos inseticidas abamectina, deltametrina e espinosade. Bioensaios de imersão de folhas foram utilizados para determinar a mortalidade, sendo os dados obtidos após 48 h de exposição aos inseticidas e submetidos à análise de Probit. A população de Bonito-PE apresentou a maior razão de toxicidade (20,2 vezes) para abamectina em relação à população de referência. Os valores de CL50s para deltametrina variaram entre 85,2 - 360,1 mg L-1, demonstrando alta sobrevivência das populações a este inseticida com relação à dose de campo (7,5 mg L-1). Entretanto, as razões de toxicidade das CL50 estimadas foram muito baixas (variando de 2,2 a 4,2 vezes). A maioria das populações apresentou razões de toxicidade para espinosade, variando de 2,3 para 5,1 vezes, embora os valores de CL demonstram alta suscetibilidade delas à dose de campo para espinosade (120 mg L-1). Apenas a população de Bonito PE apresentou resistência a abamectina, enquanto todas as populações de P. xylostella estão resistentes a deltametrina, mas suscetíveis ao espinosade particularmente devido à ausência de pressão de seleção com este nestas áreas

Optimal life stage for radiation sterilization of Anopheles males and their fitness for release.

Mating by male Anopheles mosquitoes (Diptera: Culicidae) was evaluated in the laboratory to assess fitness effects of radio-sterilization applied during different life stages of the malaria vectors An. stephensi Liston and An. gambiae Giles sensu stricto. After reproductive sterilization by gamma-irradiation (120 Gy), equal proportions of sterile and fertile (unirradiated) male adults were released into cages with virgin females and allowed to compete for matings. Radio-sterilization was applied when the males were pupae aged 0-7 h or 24-32 h, or adults aged <24 h or 24-55 h. After being radio-sterilized in the adult stage, males of both species competed effectively with unirradiated males, whereas those sterilized in the pupal stage obtained significantly fewer matings than unirradiated males from the same cohort. There was no evidence of females obtaining multiple inseminations. These findings emphasize the need to radio-sterilize males as adults in order to minimize the fitness cost. Such males may be intended for sterile insect technique population suppression or for trial releases of transgenic anophelines