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 ManagementIn addition to climate and host plant adaptations,seasonal adaptations affecting <strong>the</strong> phenology <strong>of</strong> <strong>the</strong>biocontrol agent are also likely to vary among potentialagent source populations. Many insects use photoperiod as acue for synchronizing life history events with seasonalchange in environmental conditions. When an insect ismoved from one geographic location to ano<strong>the</strong>r, itsphenology may not be synchronized to <strong>the</strong> new seasonalschedule. In Willapa Bay, <strong>the</strong> California population <strong>of</strong> P.marginata has been observed to emerge in late February, atime that may be too early for nymph survival in <strong>the</strong> coolerand longer winters <strong>of</strong> coastal Washington. Based on a match<strong>of</strong> <strong>the</strong> timing <strong>of</strong> arrival <strong>of</strong> warm temperatures, a RhodeIsland source may be <strong>the</strong> best match. However, <strong>the</strong>possibility that late emergence could reduce <strong>the</strong> number <strong>of</strong>generations produced each year makes this outcomeuncertain.Ano<strong>the</strong>r consideration in choosing a source is potentialvariation in ability to compensate for plant defenses. Apopulation from a location far<strong>the</strong>r south, such as Georgia,while poorly adapted climatically, could be better adaptedfor overcoming plant defenses to herbivory, which areknown to be greater in sou<strong>the</strong>rn Spartina plants (seePennings et al. 2005 and Katz et al. 2005 in <strong>the</strong>seproceedings). A “new association” between a sou<strong>the</strong>rnherbivore and nor<strong>the</strong>rn plant could make biocontrol moreeffective.In <strong>the</strong> spring <strong>of</strong> 2004, after obtaining permits fromUSDA-APHIS and <strong>the</strong> Washington State Department <strong>of</strong>Agriculture, four populations P. marginata were introducedinto Willapa Bay. The source populations were (1) Sausalito,San Francisco Bay, California, (2) Grayville, Rhode Island,(3) Quinby, Virginia, and (4) Jekyll Island, Georgia. Allpopulations passed through a period <strong>of</strong> quarantine in alaboratory in Davis, California before being imported intoWashington for rearing in a greenhouse.At each <strong>of</strong> five sites in Willapa Bay, we set up four 4x4-meter (m) release plots located at similar tidal elevationswithin <strong>the</strong> same Spartina meadow, but separated by at least100 m. Each plot was randomly assigned one <strong>of</strong> <strong>the</strong> foursource populations. Five thousand insects <strong>of</strong> <strong>the</strong> assignedpopulation were released into each plot by placing heavilyinfested Spartina stems clipped from five rearing plantsuniformly throughout <strong>the</strong> plot. A 100 m distance betweenrelease plots ensures that populations will remain separatelong enough to compare <strong>the</strong>ir phenology and performance.P. marginata were sampled in late September using aninsect vacuum converted from a leaf blower. Eightuniformly spaced sample points 21-cm in diameter(corresponding to <strong>the</strong> vacuum tube’s diameter) within eachrelease area were vacuumed. Adults and nymphs werecounted separately and adults were scored for wing form;P. marginata per m 2Proportion in adult stagePercent macropterous18000160001400012000100000.300.250.200.150.100.050.0080006000400020001008060402000ABGA VA CA RISource <strong>of</strong> populationGA VA CA RICSource <strong>of</strong> populationGA VA CA RISource <strong>of</strong> populationFig. 1. (A) Densities <strong>of</strong> Prokelisia marginata measured at <strong>the</strong> end <strong>of</strong> Septemberfollowing introduction <strong>of</strong> 5,000 individuals from each <strong>of</strong> four geographicsources. (B) The proportion <strong>of</strong> each source population in <strong>the</strong> adult stage at <strong>the</strong>end <strong>of</strong> September. (C) The percentage <strong>of</strong> adults in each population that weremacropterous (long-winged). Each bar represents <strong>the</strong> mean and standard errorfor five replicate populations from each source.- 269 -