Bacillus thuringiensis subspecies kurstaki reduces competition by Parapoynx diminutalis (Lepidoptera: Crambidae) in colonies of the hydrilla biological control agent Cricotopus lebetis (Diptera: Chironomidae)
Keywords:
herbivorous midge, Hydrilla verticillata, mass rearing, quality controlAbstract
The hydrilla tip mining midge, Cricotopus lebetis Sublette (Diptera: Chironomidae), is a biological control agent of the invasive aquatic weed hydrilla, Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae). Mass rearing of the midge for augmentative releases can be compromised by competition from the adventive hydrilla leafcutter moth, Parapoynx diminutalis Snellen (Lepidoptera: Crambidae). The objective of this study was to evaluate the biorational pesticide Bacillus thuringiensis (subspecies kurstaki) (Btk) for reducing competition by the moth in laboratory colonies of the hydrilla tip mining midge. Dose response bioassays with Btk were completed with both species to determine the minimum concentration that kills the moth without affecting midge production. Adult moth emergence was significantly reduced at concentrations of 2.0 mL Btk per 3.8 L of well water. A concentration of 0.2 mL Btk per 3.8 L of well water also reduced the number of emerging moths by 50%. However, midge development declined, although not significantly at the higher 2.0 mL Btk concentration compared with the control. Therefore, concentrations of 0.2 or 2.0 mL Btk per 3.8 L of well water would be appropriate for controlling competition by P. diminutalis in C. lebetis colonies. The lower concentration (0.2 mL Btk) would be appropriate for maintenance control due to its minimal impact on the midge. However, a severe infestation of P. diminutalis might justify the higher concentration of 2.0 mL Btk for maximum impact on the moth. Implementing selective pest management strategies in a biological control agent colony can help increase production and improve the quality of the insects.
Resumen
El jején minador de la punta de hidrilla, Cricotopus lebetis Sublette (Diptera: Chironomidae), es un agente de control biológico de la maleza hidrilla acuática invasora, Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae). La cría en masa del jején para la liberación aumentativa puede estar comprometida por la competencia con la polilla cortadora de hoja de hidrilla adventiva, Parapoynx diminutalis Snellen (Lepidoptera: Crambidae). El objetivo de este estudio fue evaluar el pesticida biorracional Bacillus thuringiensis (subespecie kurstaki) (Btk) para reducir la competencia por la polilla en las colonias de laboratorio del jején minador de la punta de hidrilla. Se hicieron bioensayos de la respuesta a la dosis de Btk con las dos especies para determinar la concentración mínima que mata a la polilla sin afectar la producción del jején. La emergencia de los adultos de la polilla se redujo significativamente a concentraciones de 2,0 ml Btk por 3,8 L de agua de pozo. Una concentración de 0,2 ml Btk por 3,8 L de agua de pozo también redujo el número de polillas emergentes en un 50%. Sin embargo, el desarrollo del jején se redujo, aunque no de forma significativa en la mayor concentración de 2,0 ml de Btk en comparación con el control. Por lo tanto, las concentraciones de 0,2 o 2,0 ml Btk por 3,8 L de agua así serían apropiadas para el manejo de la competencia por P. diminutalis en colonias de C. lebetis. La concentración más baja (0,2 ml Btk) sería apropiada para el mantenimiento del control debido a su impacto mínimo sobre el jején. Sin embargo, una infestación severa de P. diminutalis podría justificar la mayor concentración de 2,0 ml Btk para el máximo impacto sobre la polilla. La aplicación de estrategias de manejo de plagas selectivas en una colonia agente de control biológico puede ayudar a aumentar la producción y mejorar la calidad de los insectos.
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