Does the aquatic herbicide 2,4-D and a nonionic surfactant affect survival of salvinia weevil?

摘要

Chemical and biological control methods are often , integrated to manage unwanted plants. However, the j application of 2,4-D near giant salvinia (Salvinia molesta : Mitchell) may hinder biological control efforts by the salvinia weevil (Cyrtobagous salviniae Calder and Sands). Limited efforts . have been made to examine the susceptibility of salvinia c weevil to direct and indirect applications of 2,4-D. The c objectives of these studies were to 1) determine the direct _ and indirect impact of 2,4-Damine (0.62 and 1.85 g ai ha"1) { and nonionic surfactant (0.25% v/v) on adult salvinia weevil survivorship, and 2) determine how different application . rates of herbicide affect salvinia weevil survivorship. In a growth chamber experiment, the application of 2,4-D directly to salvinia weevil resulted in 9% mortality, whereas j. surfactant alone or in combination with the herbicide resulted in mean insect mortality of 21%. In a mesocosm experiment, the application of 2,4-D alone and in combination with surfactant to giant salvinia infested with the salvinia ￡ weevil resulted in 9 to 23% mortality, and the application of j( surfactant alone or in combination with herbicide resulted in .. 9 to 19% indirect mortality. Giant salvinia treated with 2,4-D' resulted in a significant reduction in biomass relative to the nontreated plants. The mesocosm experiment provided ^ evidence that 2,4-D alone and in combination with a surfactant has limited negative impacts on salvinia weevil mortality and future biological control programs should continue when using these methods together.