Too hot to move: temperatures during transportation might reduce the survival of salvinia weevils (Coleoptera: Curculionidae)
Abstract
The biological control agent, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) (salvinia weevil), is being used for management of the highly invasive fern Salvinia molesta Mitchell (Salvinaceae) in Louisiana and Texas, USA. The weevils and plants are transported from the nurseries and rearing facilities to the field release sites in plastic totes. Despite the increased transport of weevil-infested plants during the warmer months, limited data exist on the impact of heat stress and survivability of adult C. salviniae. Therefore, research was conducted to determine temperatures inside totes during summer transport, and to determine the upper temperature threshold for adult weevil survival. Field data demonstrated that temperatures within the totes were capable of exceeding 35 °C, and the type of lid used to secure plant material influenced internal temperature. In addition, there were no differences in temperature within the totes. Growth chamber trials determined the upper lethal time to kill 50 and 90% of the test population (ULt50 and ULt90) at 35 °C was 27.5 and 42.8 hours, respectively, while at 40 °C, the ULt50 and ULt90 was 15.0 and 25.0 hours, respectively. As the temperature increased to 50 °C, the calculated ULt50 and ULt90 values were 5.0 and 11.0 minutes, respectively. These data provided evidence that C. salviniae mortality occurs more rapidly as the temperature increases, especially > 45 °C, and that extreme temperatures can occur within transportation totes.
Resumen
El agente de control biológico, Cyrtobagous salviniae Calder y Sands (Coleoptera: Curculionidae), está siendo utilizado para el manejo de la maleza altamente invasiva, Salvinia molesta Mitchell (Salvinaceae), en Luisiana y Texas, E.U.A. Los gorgojos y las plantas son transportados desde los criaderos hacia los sitios de liberación en envases de plástico. A pesar del mayor transporte de plantas infestadas con gorgojos durante los meses calientes, hay datos limitados del impacto del estrés por calor y sobrevivencia de adultos de C. salviniae. Por consiguiente, se hizo una investigación para determinar las temperaturas dentro de los envases durante el verano y determinar el nivel crítico para la sobrevivencia de adultos del gorgojo a altas temperaturas. Datos de campo demostraron que temperaturas dentro de los envases son capaces de exceder 35 °C y el tipo de tapa del envase influenció su temperatura interna. Además, no hubo diferencias de temperatura dentro de los envases. Ensayos en cámaras de crecimiento determinaron que el tiempo letal para matar el 50 y 90% de la población muestra (Tl50 y Tl90) a 35 °C fue de 27.5 y 42.8 horas, respectivamente, mientras que a 40 °C, el Tl50 and Tl90 fue 15.0 y 25.0 horas, respectivamente. Como las temperaturas incrementaron hasta 50 °C, los valores de Tl50 and Tl90 fueron 5.0 y 11.0 minutos, respectivamente. Estos datos son evidencia que la mortalidad de C. salviniae ocurre más rápidamente como las temperaturas incrementan, especialmente a más de 45 °C, y que temperaturas extremas pueden ocurrir dentro de los envases de transporte.
Key Words: Cyrtobagous salviniae; heat stress; Salvinia molesta; thermal tolerance
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