Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 4: Spartina Control and ManagementECOLOGICAL INVESTIGATIONS OF NATURAL ENEMIES FOR AN INTERSTATE BIOLOGICALCONTROL PROGRAM AGAINST SPARTINA GRASSESD. VIOLA 1,2 ,L.TEWKSBURY 1 AND R. CASAGRANDE 11Department <strong>of</strong> Plant Sciences, University <strong>of</strong> Rhode Island, Kingston, RI 028812dviola@myrealbox.comSpartina alterniflora (smooth cordgrass) is a dominant member <strong>of</strong> salt marsh communities in itsnative range along <strong>the</strong> East Coast <strong>of</strong> <strong>the</strong> United States as well as an introduced invasive in severalWest Coast intertidal areas. In 2000, a biological control agent, Prokelisia marginata, was releasedin Willapa Bay, Washington, USA where S. alterniflora was rapidly spreading. Despiteestablishment <strong>of</strong> this agent, <strong>the</strong> invasive population was not brought under control. Although <strong>the</strong>natural enemies <strong>of</strong> S. alterniflora have been previously catalogued, little has been written regarding<strong>the</strong>ir ecology, with <strong>the</strong> exception <strong>of</strong> P. marginata. The purpose <strong>of</strong> this study was to provideadditional information on <strong>the</strong> ecology <strong>of</strong> insect herbivores <strong>of</strong> S. alterniflora in Rhode Island insupport <strong>of</strong> a larger effort to develop biological control agents for <strong>the</strong> West Coast.An intensive survey <strong>of</strong> insect species found on S. alterniflora in Rhode Island was conducted todescribe <strong>the</strong> composition <strong>of</strong> <strong>the</strong> insect herbivore community. Vacuum samples taken at both highand low marsh locations facilitated <strong>the</strong> characterization <strong>of</strong> species assemblages. Our results suggestthat <strong>the</strong>re is little variation in insect herbivore species richness among Rhode Island salt marshes.Damage due to Chaetopsis spp. is easily observed in <strong>the</strong> field, but <strong>the</strong> frequency <strong>of</strong> damaged stemsvaries greatly among sites. Additional research is needed to determine <strong>the</strong> factors responsible forthis variation.Keywords: Spartina alterniflora, Chaetopsis, biological control, natural enemies, invasive speciesINTRODUCTIONSpartina grasses have become serious invasive pests inWest Coast intertidal regions since <strong>the</strong>ir introduction in <strong>the</strong>late 1800s. Many Pacific intertidal areas are predominantlyexposed mudflats at low tide, and Spartina is rapidlycolonizing <strong>the</strong>se areas. Its effects range from <strong>the</strong> reduction<strong>of</strong> valuable feeding habitat for migratory shorebirds to <strong>the</strong>possible collapse <strong>of</strong> some areas’ shellfishing industries.Traditional control methods such as mowing, tilling, andherbicide application were not yet effective or economical at<strong>the</strong> writing <strong>of</strong> this article, and a long-term solution was stillbeing sought. In 2000, a biological control agent, <strong>the</strong>planthopper Prokelisia marginata Van Duzee (Homoptera:Delphacidae), was released in Willapa Bay, Washington, tocontrol Spartina alterniflora Loisel. (Grevstad et al. 2003),but <strong>the</strong> invasive population was not brought under controldespite establishment <strong>of</strong> this control agent.Past studies documenting <strong>the</strong> insect fauna in Spartinamarshes (Davis and Gray 1966; Denno 1977; Vince et al.1981; Newton 1984) have demonstrated <strong>the</strong> diversity <strong>of</strong> <strong>the</strong>associated insect communities, but relatively few havefocused on New England marshes. The purpose <strong>of</strong> this studywas to ga<strong>the</strong>r information on <strong>the</strong> ecology <strong>of</strong> insec<strong>the</strong>rbivores <strong>of</strong> S. alterniflora in Rhode Island in support <strong>of</strong> alarger effort to develop biological control agents for releasein Willapa Bay.METHODSThirteen Rhode Island salt marshes (Fig. 1) wereFig. 1: Vacuum samples were collected at sites marked with a circle.Vacuum and stem samples were collected at sites marked with a star.- 273 -