Biological control of invasive water primroses, Ludwigia spp., in the United States: A feasibility assessment

Abstract

Exotic water primroses are aggressive invaders in both aquatic and riparian ecosystems worldwide. Water primrose [Ludwigia hexapetala (Hook. & Arn.) Zardini, Gu & P. H. Raven], floating primrose-willow [Ludwigia peploides (Kunth) P. H. Raven subsp. peploides], floating primrose-willow [Ludwigia peploides (Kunth) P. H. Raven subsp. montevidensis (Spreng.) P. H. Raven], Uruguay waterprimrose [Ludwigia grandiflora (Michx.) Greuter & Burdet], and the winged waterprimrose (Ludwigia decurrens Walter) have naturalized in aquatic ecosystems in the United States and are the focus of this study. The only control tools available to resource managers for suppression of Ludwigia spp. are physical and chemical methods, but these options are often limited in effectiveness and by costs and regulatory constraints. Biological control is an alternative that can be used alone or in combination with traditional methods. The purposes of this study were to explore the feasibility of a biological control program targeting problematic Ludwigia spp. in the United States and to propose a list of plant species for consideration during host range studies of candidate herbivores. A variety of native insects feed on Ludwigia spp. in the United States; however, most are generalists and have no appreciable influence on plant growth or fitness. Foreign exploration for natural enemies of Ludwigia spp. in South America suggests that a rich herbivore fauna is associated with the plants in their native range. Candidate agents must have section-level host specificity because several Ludwigia spp. are also native to the United States. Therefore, the plant test list is designed to distinguish herbivore host ranges based on the phylogenetic relationships of the test plants. For those Ludwigia spp. for which eradication may no longer be possible because the weed is regionally abundant, biological control may be the primary control option when traditional methods are not feasible.