Herbivore suppression of waterlettuce in Florida, USA

Authors: Foley Iv, Jeremiah; WILLIAMS, JACOB - Virginia Tech; Pokorny, Eileen; TIPPING, PHILIP - Retired ARS Employee

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2022
Publication Date: 1/4/2023
Citation: Foley Iv, J.R., Williams, J., Pokorny, E.N., Tipping, P.W. 2023. Herbivore suppression of waterlettuce in Florida, USA. Biological Control. 179. Article 105149. https://doi.org/10.1016/j.biocontrol.2023.105149.
DOI: https://doi.org/10.1016/j.biocontrol.2023.105149

Interpretive Summary: Invasive aquatic plants are managed across the world using a handful of treatment options, including but not limited to herbicide, mechanical and physical removal, and biological control. In south Florida, waterlettuce (Pistia stratiotes) is considered a highly invasive weed and has been target for biological and chemical control for the past half century. However, land managers often disregard the contributions from biological control agents though repeated applications of herbicides. The aim of this study was to document the aggerate impact native and classical biological control agents have on reducing waterlettuce biomass accumulation and percent coverage across three sites in south Florida. Four species (E. obliteralis, S. multiplicalis, O. terebrantis, and N. affinis) were found at every field site. At the end of the experiment, plots exposed to unrestricted herbivory contained 63.1% less biomass and covered 32.0% less surface area compared to plots with restricted herbivory. These results indicate that naturally occurring and introduced species are suppressing the growth of waterlettuce populations in the field in Florida. Future research will examine the synergistic potential of actively managing herbicides and herbivorous arthropods to suppress waterlettuce.

Technical Abstract: Waterlettuce, Pistia stratiotes L. (Araceae: Pistieae) is an invasive free-floating aquatic weed found throughout the world that has been targeted for control using various methods including classical and conservation biological control and herbicides. In Florida, herbicides are the primary strategy employed by land managers, often without regard to the impact of herbivorous arthropods including Samea multiplicalis (Lepidoptera: Crambidae) Guenee, Elophila [=Synclita] obliteralis (Crambidae) Walker, Argyractis [=Petrophila] drumalis (Lepidoptera: Crambidae), Draeculacephala inscripta (Hemiptera: Cicadellidae) VanDuzee, Rhopalosiphum nymphaeae (Hemiptera: Aphididae) L., Orthogalumna terebrantis Wallwork (Acarina: Galumnidae), and Neohydronomus affinis (Coleoptera: Curculionoidea) Hustache. A series of field experiments from 2009 to 2012 were conducted at three sites in Florida to quantify the levels of suppression by these species, using an insecticide-check approach to produce restricted and unrestricted herbivory conditions. Four of the species (E. obliteralis, S. multiplicalis, O. terebrantis, and N. affinis) were found at every field site. At the end of the experiment, plots exposed to unrestricted herbivory contained 63.1% less biomass and covered 32.0% less surface area compared to plots with restricted herbivory. These results indicate that naturally occurring and introduced species are suppressing the growth of waterlettuce populations in the field in Florida. Future research will examine the synergistic potential of actively managing herbicides and herbivorous arthropods to suppress waterlettuce.