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 Managementlarvae <strong>of</strong> <strong>the</strong>se flies develop inside young S. alterniflorashoots, feeding on meristem tissue and developing leaves.The result is death <strong>of</strong> <strong>the</strong> shoot tip and no flower productionin nearly 100% <strong>of</strong> <strong>the</strong> stems that are infested. Both speciesoccur from Florida to Maine. The potency <strong>of</strong> <strong>the</strong>se flies liesin <strong>the</strong> fact that a single larva can kill a shoot. Bycomparison, it takes approximately 200 planthoppers to killa shoot (Daehler and Strong 1997). In our surveys, we foundseveral sites where <strong>the</strong> rate <strong>of</strong> shoot death due to this insectwas greater than 50%.O<strong>the</strong>r promising candidates include <strong>the</strong> sapsuckinginsects, Trigonotylus uhleri, Haliaspis spartinae, andProkelisia dolas. All three <strong>of</strong> <strong>the</strong>se species have <strong>the</strong>advantage that <strong>the</strong>y already occur in California, where <strong>the</strong>native Spartina foliosa occurs. Thus, introduction <strong>of</strong> <strong>the</strong>seinsects to Washington does not pose a risk to S. foliosa if<strong>the</strong>y were to disperse from Washington to California. T.uhleri is a mirid bug that feeds primarily on <strong>the</strong> tips <strong>of</strong> <strong>the</strong>leaves. H. spartinae is a scale insect that occurs in lowdensities on <strong>the</strong> Atlantic Coast but can be found at very highdensities in San Francisco Bay. P. dolas is a close relative <strong>of</strong>our current biocontrol agent. P. dolas has been shown to bemore tolerant <strong>of</strong> low host quality than P. marginata (Dennoet al. 2000), which suggests that it could be a potentbiocontrol agent. However, this species has been shown tooutcompete P. marginata (Denno et al. 2000). This could bedetrimental to <strong>the</strong> overall biocontrol program because unlikeP. marginata, P. dolas is unable to exploit <strong>the</strong> majority <strong>of</strong>Spartina occuring in mid to lower tidal elevations.UPDATE ON BIOCONTROL PROGRAMMuch has happened with regard to control <strong>of</strong> Spartinain Willapa Bay and Puget Sound since this report was originallyprepared in 2004. In particular, <strong>the</strong> state and federalagencies involved in <strong>the</strong> control program increased capacityand improved <strong>the</strong> effectiveness <strong>of</strong> <strong>the</strong> herbicide control treatmentsand eventually sprayed all Spartina-infested areas inWashington including biocontrol sites in an effort to eradicate<strong>the</strong> plant. As <strong>of</strong> 2007, prior to herbicide treatment <strong>of</strong><strong>the</strong> last remaining biocontrol site, <strong>the</strong> P. marginata populationwas increasing and spreading in <strong>the</strong> north end <strong>of</strong> WillapaBay with measured densities <strong>of</strong> more than 10,000 perm 2 , sufficient to cause browning <strong>of</strong> <strong>the</strong> plants over a twoacrearea. The full impact <strong>of</strong> biological control may never beknown. If P. marginata is capable <strong>of</strong> persisting on <strong>the</strong> sparseshoots that remain, it may help suppress any reinvasion <strong>of</strong>Spartina if traditional control methods are discontinued.CONCLUSIONSThe biological control agent, Prokelisia marginata, hasa demonstrated capacity for reducing Spartina biomass andseed set in Washington. In <strong>the</strong> first few years <strong>of</strong> <strong>the</strong>biocontrol program, poor overwintering survival <strong>of</strong> nymphskept populations from growing from year to year. With <strong>the</strong>introduction <strong>of</strong> P. marginata ecotypes from <strong>the</strong> East Coast,we are confident that we have provided <strong>the</strong> best opportunityfor P. marginata to be successful. P. marginata from RhodeIsland outperformed P. marginata from o<strong>the</strong>r locations in<strong>the</strong> first summer after release. Impacts to Spartina in <strong>the</strong> lab(Daehler and Strong 1997) and in field cages (Grevstad et al.2003) have been clearly demonstrated. Impacts on a muchlarger scale were beginning to be seen in 2007 prior toherbicide treatment <strong>of</strong> biocontol sites.The success <strong>of</strong> a biological control program for Spartinacould be fur<strong>the</strong>r improved with <strong>the</strong> screening andintroduction <strong>of</strong> additional biocontrol agents. Severalpromising candidate agents have been selected from adiverse community <strong>of</strong> insects and o<strong>the</strong>r organisms that use S.alterniflora as a host in <strong>the</strong>ir native range. Biological controlcould be a valuable tool in o<strong>the</strong>r parts <strong>of</strong> <strong>the</strong> world whereSpartina has invaded, especially where complete eradicationis too expensive or not feasible. Even where traditionalcontrol programs are underway, biological control cancontribute to Spartina reduction in an integrated weedmanagement approach, or it can serve as a backup in <strong>the</strong>case that complete eradication is not achieved.Unfortunately, San Francisco Bay is not a good targetlocation for biological control because <strong>of</strong> <strong>the</strong> risk to <strong>the</strong>native S. foliosa. However, it would be an excellent option inChina, New Zealand, and Australia where <strong>the</strong>re are no nativeSpartina species.ACKNOWLDEGMENTSWe would like to acknowledge <strong>the</strong> following agenciesand sponsors who have made <strong>the</strong> Spartina biocontrolprogram possible: National Sea Grant Program, U.S. Fishand Wildlife Service, U.S. Department <strong>of</strong> Fish and Wildlife,Coastal Resource Alliance, Washington State Department <strong>of</strong>Agriculture, Washington State Department <strong>of</strong> NaturalResources, and <strong>the</strong> Willapa National Wildlife Refuge. Wewould also like to thank <strong>the</strong> following individuals who havecontributed to <strong>the</strong> program in a wide variety <strong>of</strong> ways: BobDenno, Dino Garcia-Rossi, Robin Switzer, Carol O’Casey,Deanna McQuarrie, Hea<strong>the</strong>r Davis, Allison Fisher, KimPatten, Kathleen Sayce, Janie Civille, Todd Brownlee,Wendy Brown, Charlie Stenvall, Teri Butler, Dave Heimer,Kyle Murphy, Sue Moreno, Dick Casagrande, David Viola,and Lisa Tewksbury.REFERENCESCruttwell-McFayden, R.E. 1998. Biological control <strong>of</strong> weeds. AnnualReview <strong>of</strong> Entomology 43:369-393.Davis, L.V. and I.E. Gray. 1966. Zonal and seasonal distribution <strong>of</strong>insects in North Carolina salt marshes. Ecological Monographs36:275-295.Davis, H.G., D.R. Strong and D. Garcia-Rossi. 2002. The use <strong>of</strong>molecular assays to identify plant pathogenic organisms vectoredby biological control agents. BioControl 47: 487-497.- 271 -