Too Hot to Move: Temperatures during Transportation Might Reduce the Survival of Salvinia Weevils (Coleoptera: Curculionidae)

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.