Limited variations in susceptibility to an insecticidal double-stranded RNA (dsvATPaseE) among a laboratory strain and seven genetically differentiated field populations of Tribolium castaneum.

There has been a considerable growth in interest to use RNA interference (RNAi) as a novel insect pest management strategy in the past 10 years. However, there has been virtually no information on insect population variations in response to double-stranded RNA (dsRNA) molecules. The objective of this study was to generate baseline susceptibilities of the red flour beetle (Tribolium castaneum) to an insecticidal dsRNA targeting vacuolar H+-ATPase subunit E gene (dsvATPaseE), and correlate the susceptibility data with sequence and expression variations of the target gene (vATPaseE), expression variations of the RNAi core genes, and overall genetic differences among a laboratory strain and seven geographical field populations of T. castaneum collected in China. Our results showed limited variations in the LD50 values of dsvATPaseE, which ranged from 0.10 to 0.29 ng/larva among the laboratory strain and the seven field populations. Considering the overlapping of the 95% confidence intervals of their LD50 values, there were no significant differences among the laboratory strain and field populations. We also found limited sequence polymorphisms and low frequencies of the polymorphisms of vATPaseE, and limited variations (<2-fold) of the endogenous expression of vATPaseE among the laboratory strain and field populations. However, we found considerable genetic variations among the individuals within each field population for most of eight loci and moderate to large genetic variations among the field populations. These results demonstrated that although the genetic variabilities were considerable among these field populations, the efficiency of RNAi targeting vATPaseE was highly consistent in T. castaneum. Our study provides work frames of resistance risk assessment for RNAi-based insect pest management programs.

Potencial inseticida de óleos essenciais sobre Tribolium castaneum em milho armazenado / Insecticidal potential of essential oils on Tribolium castaneum in stored maize

RESUMO O presente trabalho teve como objetivo investigar o potencial inseticida de óleos essenciais de Croton heliotropiifolius, Croton pulegiodorus, Myracrodruon urundeuva e Ocimumbasilicum sobre adultos de Tribolium castaneumem milho armazenado. Para cada óleo foram realizados bioensaios de fumigação, repelência e o efeito sobre a taxa instantânea de crescimento (ri), em cinco concentrações (0; 5; 10; 15 e 20 μL). Os bioensaios foram conduzidos sob condições constantes de temperatura (28±2 ºC), umidade relativa (70±5%) e escoto fase de 24 horas. Nos testes de fumigação diferentes concentrações dos óleos foi aplicado em tiras de papel filtro presas na parte inferior da tampa da câmara de fumigação (1,5L), a qual continha 20 gramas de substrato alimentar e 10 insetos adultos de T. castaneum não sexados. A mortalidade dos insetos foi avaliada após 48 horas de exposição. Os testes de repelência foram efetuados em arenas compostas por dois frascos ligados a uma caixa central. Em um frasco foi depositado o substrato alimentar com diferentes concentrações do óleo essencial, e, no outro, foi depositado apenas alimento (testemunha). Dez insetos adultos foram liberados na caixa central, ficando expostos por 5 dias para avaliação da preferência. Nos bioensaios de fumigação observou-se atividade inseticida do óleo essencial de M. urundeuva sobre adultos de T. castaneum. Nos bioensaios de repelência, todos os óleos testados apresentaram efeito repelente. A emergência de T. castaneumreduziu entre 33 e 100% quando foram criados em pó de milho tratado com os óleos essenciais. Os óleos essenciais de C. pulegiodorus e O. basilicum ocasionaram redução do crescimento populacional de T. castaneum em grãos de milho tratados. Os óleos testados demonstraram ser uma alternativa eficiente de controle para o uso nos programas de manejo de T. castaneum em unidades armazenadoras.

ABSTRACT The current work aimed at to investigate the insecticide potential of essential oils of Croton heliotropiifolius, Croton pulegiodorus, Myracrodruon urundeuva and Ocimum basilicum on adults of Tribolium castaneum in stored maize. For each oil, it were performed fumigation tests, repellency and the effect on the instantaneous rate of increase (ri), in five concentrations (0; 5; 10; 15 e 20 μL). Bioassays were carried out under constant temperature conditions (28±2 °C), relative humidity (70±5%) and scot phase of 24 hours. In fumigation different concentrations of test oils were applied on filter paper strips attached on the bottom of the fumigation chamber cover (1.5 L), which contained 20 grams of food substrate and 10 unsexed adults of T. castaneum. The insect mortality was recorded after 48 hours of exposure. The repellency tests were performed in arenas composed of two pots connected to a central box. In a pot it was deposited feed substrate, with concentrations of the essential oil, in the other pot (control) it was deposited only food. Ten adult insects were released in the central box, being exposed for 5 days to evaluate the preference. In the fumigation tests, insecticide activity of the essential oil of M. urundeuva was observed on adults of T. castaneum. In the repellency tests, all the tested oils presented repellent effect. The emergency of T. castaneumreduced between 33% and 100% when they were in the powdered maize treated with the essential oils. Maize grains treated with C. pulegiodorus and O. basilicum essential oils caused a significant decrease in the populations of T. castaneum. The tested oils proved to be an efficient control alternative for the use in managing programs of T. castaneum in storing units.

Pesticidal and pest repellency activities of a plant derived triterpenoid 2α, 3ß, 21ß, 23, 28-penta hydroxyl 12-oleanene against Tribolium castaneum

BACKGROUND: Tribolium castaneum (Herbst) is a major pest of stored grain-based products, and cause severe damage to cereal grains throughout the world. The present investigation was aimed to determine the pesticidal and pest repellent activities of 2α,3ß,21ß,23,28-penta hydroxyl 12-oleanene against T. castaneum. The compound 2α,3ß,21ß,23,28-penta hydroxyl 12-oleanene is a triterpenoid which was isolated from the roots of Laportea crenulata Gaud. Surface film technique was used for pesticidal screening, whereas, pest repellency property of the triterpenoid was determined by filter paper disc method. RESULTS: At 24 hours of exposure duration, significant mortality records (80% and 86%) were observed at doses 0.88 and 1.77 mg/cm². No significant change in mortality records was observed when duration of exposure was increased up to 48 hours. The triterpenoid showed significant repellency activity at doses 0.47 and 0.94 mg/cm². CONCLUSION: These data suggest that the triterpenoid 2α,3ß,21ß,23,28-penta hydroxyl 12-oleanene possess both pesticidal and pest repellency activities against T. castaneum and can be used in controlling the pest of grain-based products.

Relación entre la actividad de esterasas y la resistencia a malatión en una cepa de Tribolium Castaneum / Relation activity from enterase and t.castaneum malathion resistant

Se estudiaron comparativamente las esterasas de las cepas de Tribolium castaneum ULP (suceptible) y ML (resistente a malatión). La actividad de esterasas que hidrolizan acetato de * y ß naftol presentes en homogenatos de T. castaneum fue mayor en la cepa susceptible ML, mientras que la actividad frente al acetato de tiofenilo fue similar en ambas cepas. La distribución subcelular de la actividad esterástica frente al PTA mostró diferencias en ambas cepas. En los homogenatos de insectos de la cepa susceptible se observó que a mayor velocidad de centrifugación el sobrenadante resultó considerablemente más activo en la hidrólisis de acetato de tiofenilo. Se supone que ese resultado se debe a la presencia de un inhibidor endógeno no dializable, de peso molecular tal que puede ser parcialmente precipitado a 10.000g y en mayor medida a 100.000g. Los zimogramas de esterasas no inhibibles por eserina separadas por electroforesis en gel de poliacrilamida y reveladas con * y ß naftilacetato, mostraron, en todos los casos, una única banda que fue clasificada como aril o acetil esterasa. Los resultados descriptos encuadran en la teoría de la aliesterasa mutada, postulada para casos de resistencia al malatión, descriptos en otas especies de insectos