Evaluation of Insecticides Against the Western Flower Thrips, Frankliniella occidentals (Thysanoptera: Thripidae), in the Laboratory
Abstract
To evaluate insecticide efficacy against the western flower thrips, Frankliniella occidentalis (Pergande), the first step was to select a host suitable for rearing sufficient numbers of this pest. The influence on the development and survival rates of this thrips of each of 3 selected leguminous hosts, Canavalia gladiata (Jacq.) DC, Lablab purpureus (L.) Sweet and Phaseolus vulgaris L., was examined and compared to the other in the laboratory. Results showed that the number of newly hatched larvae (543.20), the survival rates of 2nd to 4th instar (89.12%), and the eclosion (73.17%) on C. gladiata were significantly higher than on L. purpureus and P. vulgaris, and also the developmental time from egg to adult was the shortest on C. gladiata (10.15 d). Therefore, C. gladiata was selected as the best host among these legumes for rearing the thrips in the laboratory. Thirty-six insecticides commonly used in China to protect flowers and vegetables were chosen from 8 chemical classes for assay using a glass-vial method to evaluate their toxicities against thrips larvae in a laboratory. Based on LC50 values, and on the need to rotate and alternate the application of insecticides, 12 highly efficacious insecticides from different IRAC mode of action groups were evaluated against adult females. Although the ranking of toxicities to adults was slightly different from that to larvae, the results showed that the insecticides with high efficacy against larvae were also effective against adults. These findings will facilitate the selection of insecticides for effective control of western flower thrips and for developing insecticide resistance management strategies.Para evaluar la eficacia de insecticidas contra el trips, Frankliniella occidentalis (Pergande), el primer paso fue seleccionar un hospedero adecuado para criar un número suficiente de esta plaga. El efecto de 3 plantas leguminosas hospederas, Canavalia gladiata (Jacq.) DC, Lablab purpureus (L.) Sweet y Phaseolus vulgaris L., sobre la tasa de desarrollo y la supervivencia de los trips fue examinado y comparado en el laboratorio. Los resultados mostraron que el número de larvas neonatas (543.20), la tasa de supervivencia desde el segundo hasta el cuarto estadio (89.12%), y la eclosión (73.17%) en C. gladiata fueron significativamente mayores que en L. purpureus y P. vulgaris; también, el tiempo de desarrollo de huevo a adulto fue más corto en C. gladiata (10.15 d). Por lo tanto, C. gladiata fue seleccionado como el mejor hospedero entre estas leguminosas para la cría de los trips en el laboratorio. Se analizaron 36 insecticidas de 8 clases químicas diferentes comúnmente usados para proteger flores y hortalizas. Se utilizó un bioensayo con viales de vidrio para evaluar su toxicidad contra larvas de trips en el laboratorio. Basadose en resultados de CL50, 12 insecticidas altamente eficaces y de diferentes grupos (IRAC) de modo de acción fueron seleccionados para evaluar su toxicidad contra las hembras adultas. Aunque la clasificación de la toxicidad en los adultos fue ligeramente diferente a la de las larvas, los resultados mostraron que los insecticidas con una alta eficacia contra las larvas también fueron efectivos contra los adultos. Estos hallazgos ayudarán en la selección de insecticidas para el control efectivo de esta especie de trips y para desarrollar estrategias de manejo de resistencia a insecticidas.
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