DOI: 10.5061/dryad.8pk0p2nt9
title: From ecological menace to roadside attraction: 28 years of evidence support successful biocontrol of purple loosestrife

description: Introduction and spread of non-native plants provide ecologists and
 evolutionary biologists with abundant scientific opportunities. However,
 land managers charged with preventing ecological impacts face financial
 and logistical challenges to reduce threats by introduced
 species.  The available toolbox (chemical, mechanical, or
 biological) is also rather limited.  Failure to permanently
 suppress introduced species by mechanical and chemical treatments may
 result in biocontrol programs using host-specific insect
 herbivores.  Regardless of the chosen method, long-term
 assessment of management outcomes not just on the target species, but also
 on associated biota, should be an essential component of management
 programs. However, data to assess whether management results in desirable
 outcomes beyond short-term reductions of the target plant are
 limited.  Here we use implementation of a biocontrol program
 targeting a widespread wetland invader, Lythrum salicaria (purple
 loosestrife), in North America to track outcomes on the target plant over
 more than two decades in New York State.  After extensive
 testing, two leaf-feeding beetles (Galerucella calmariensis and G.
 pusilla; hereafter ‘Galerucella’), a root-feeding weevil (Hylobius
 transversovittatus) and a flower-feeding weevil (Nanophyes marmoratus)
 were approved for field releases.  We used a standardized
 monitoring protocol to record insect abundance and L. salicaria stem
 densities and heights in 1m2 permanent quadrats at 33 different wetlands
 and followed sites for up to 28 years.  As part of this long-term
 monitoring in 20 of these wetlands, we established a factorial experiment
 releasing either no insects (control), only root feeders, only leaf
 beetles, or root- and leaf-feeders. We document reduced L. salicaria
 occupancy and stem densities following insect releases over time,
 irrespective of site-specific differences in starting plant communities or
 L. salicaria abundance.  We could not complete our factorial
 experiment because dispersal of leaf beetles to root-feeder-only and
 control sites within five years invalidated our experimental controls. Our
 data show that it took time for significant changes to occur, and
 short-term studies may provide misleading results, as L. salicara stem
 densities initially increased before significantly decreasing. Several
 decades after insect releases, pre-release predictions of significant
 purple loosestrife declines have been confirmed.
description: We worked at 33 sites (mix of federal, state, and private
 ownership) varying in size from a few hundred square meters to &gt;10
 ha across New York State.  Initially, most sites (old fields, wetlands,
 marshes, and impoundments) were dominated by<em> L.
 salicaria</em>, although some releases occurred where managers
 documented only small patches.  Water levels varied through time,
 reflecting natural variation in precipitation patterns, beaver activity,
 and intentional manipulations by wetland managers and private landowners.
  We monitored each site for a period of 15 to 28 years, starting the year
 insects were first released.  Releases included one or several of the
 following species: two leaf-feeding beetles (<em>Galerucella
 calmariensis</em> and <em>G. pusilla</em>), a
 root-feeding weevil (<em>Hylobius</em>
 <em>transversovittatus</em>), and a flower-feeding weevil
 (<em>Nanophyes marmoratus</em>).   At each
 site we established 1 to 15 1 m<sup>2</sup> permanent quadrats
 spaced 5–50 m apart.  Presence of <em>L. salicaria</em> was a
 pre-requisite for initial quadrat placement, as the region had well
 established long-term presence of <em>L. salicaria</em> and
 populations were stable and not undergoing short-term fluctuations.  The
 number of quadrats and distance between quadrats was dictated by
 <em>L. salicaria</em> population size.  We used 1.5 m tall PVC
 (2.53 cm diameter) poles to mark each corner of each quadrat, and recorded
 GPS position and hand-drew maps indicating distance and azimuth to help
 relocate quadrats.  Over the 28 years, individual poles and occasionally
 all poles of a quadrat disappeared; we used GPS and field notes to
 re-establish quadrats as close to the original position as
 possible.  We initially visited all sites twice
 annually. At each site, we recorded detailed data about <em>L.
 salicaria</em> growth and reproduction, presence and abundance of
 released insects and co-occurring plant species. In June we counted
 <em>L. salicaria</em> stem density, estimated <em>L.
 salicaria</em> cover (%), and recorded
 <em>Galerucella</em> abundance using timed counts (1 min each
 for eggs, adults, and larvae), and made visual assessments of leaf area
 removed (%).  We did not record presence for <em>H.
 transversovittatus</em> as larvae feed in roots, and adults are
 night active, preventing detection without destructive sampling.  We also
 did not record presence of <em>N. marmoratus</em>.  However,
 during our last sampling in 2019, we recorded presence of flower feeders
 and assessed root-feeder presence at all sites, except those that were
 permanently flooded, by excavating rootstocks and checking for larval
 feeding damage. In September, in each quadrat we recorded <em>L.
 salicaria</em> stem density and cover (%) and, for the five tallest
 stems, height, number of inflorescences, length of the tallest
 inflorescence, and number of flower buds in the central 5cm of that
 inflorescence.  Depending on insect releases, we recorded data for
 variable time periods at each site between 1996 and 2007, and again at all
 33 sites in August and September 2019.  Data was
 entered into excel, formatted, and then analyzed using R.  Please see the
 associated manuscript for more details.
description: Excel or Text-editor R or R studio
description: # From ecological menace to roadside attraction: 28 years of evidence
 support successful biocontrol of purple loosestrife
 doi:10.5061/dryad.8pk0p2nt9 ## Description of the data and file structure
 Data are typically summarized by unique quadrat by time treatment
 combinations (i.e., data rows). Which csv file is needed for each analysis
 is explained within the annotations of the associated R scripts.
 "NA" represents 'missing' values in the dataset. Some
 important variables of note in the data files include area (region of
 state where site was located), month (month of data collection; either
 'June' for summer monitoring or ‘Sept’ for fall monitoring), and
 pl.density (number of stems per permanent 1m<sup>2</sup>
 quadrat). Descriptions of other variables are also found in the main text
 in addition to the detail provided herein. ### Column descriptions by csv
 file: #### dispersal\_distance\_in\_montezuma.csv Note: this represents
 summary data from only a subset of the monitored sites. This file only
 contains data from sites within the Montezuma region, as this was the only
 region in which we established a factorial experiment releasing either no
 insects (control), only root feeders, only leaf beetles, or root- and
 leaf-feeders. We further subset the data in this file to look only at
 sites where leaf-feedings (Galerucella) had not been intentionally
 released, to better assess how long it takes Galerucella to disperse from
 neighboring release sites. Column descriptions are as follows: * area -
 region of state where site was located (overall, we sampled four regions:
 'hudson' [Hudson River Valley, NY], 'mont' [Montezuma,
 NY], 'tnc' [Western New York sites under stewardship of The
 Nature Conservancy], and 'west' [Western Lake Ontario sites in
 NY]; this subset dataset only includes data from Montezuma, NY) * site -
 name of sampled site (i.e., unique site identifier) * latitude - latitude
 of site in decimal degrees * longitude - longitude of site in decimal
 degrees * insect treatment - which insects were intentionally released as
 part of purple loosestrife biocontrol program (this dataset is subset, so
 only contains two treatments: control = no insects were released, hyl =
 only *Hylobius transversovittatus* were released) * closest.site.with.gal
 - name of closest neighboring site where *Galerucella* sp. were
 intentionally released * closest.lat - the latitude (in decimal degrees)
 of the closest neighboring site where *Galerucella* sp. were intentionally
 released * closest.long - the longitude (in decimal degrees) of the
 closest neighboring site where *Galerucella* sp. were intentionally
 released * distance.in.meters - the distance (in meters) between the site
 and the closest neighboring site where *Galerucella* sp. were
 intentionally released * # of quads - the number of permanent
 1m<sup>2</sup> quadrats that were monitored within the site *
 date of insect releases - if applicable, the year of insect releases at
 the site; The 'H' following the year indicates that only
 *Hylobius transversovittatus* were released at the site; many rows do not
 have data for this column, as there were no insects released at those
 sites * first year Galerucella confirmed to be established? - first year
 that *Galerucella* were observed at the site * date since earliest Gal.
 release - Number of years since *Galerucella* were first released at the
 site identified in the "closest.site.with.gal" site ####
 formatted.5.tallest.csv Note: Only the five-tallest stems within each
 permanent 1m<sup>2</sup> quadrat were measured for this
 dataset; each unique sampling year by quadrat combination therefore has
 five rows. If there were less than five stems within a quadrat during a
 specific sampling time, we still included a row for the
 'missing' stems, but left the columns labeled
 "pl.height", "pl.fertile",
 "pl.number.inflor", "pl.inflorescence.length", and
 "pl.number.flowers" as "NA" for this row in the
 dataset. * row.order - the order of the rows in the original, unformatted
 dataset * area - region of state where site was located (we sampled four
 regions: 'hudson' [Hudson River Valley, NY], 'mont'
 [Montezuma, NY], 'tnc' [Western New York sites under stewardship
 of The Nature Conservancy], and 'west' [Western Lake Ontario
 sites in NY]) * site - name of sampled site (i.e., unique site identifier)
 * trt - which insects were intentionally released as part of purple
 loosestrife biocontrol program (four treatments: control = no insects were
 released, gal = only *Galerucella* sp. were released, gal.hyl = both
 *Galerucella* sp. and *Hylobius transversovittatus* were released,
 gal.hyl.nan = *Galerucella* sp., *Hylobius transversovittatus*, and
 *Nanophyes marmoratus* were all released [note: this only applies to one
 site], hyl = only *Hylobius transversovittatus* were released) * year -
 year data was collected * year.of.first.release - year insects were first
 released at the site * num.years.after.release - number of years at time
 of data collection after the first insects were released at the site
 (referred to as 'time' within the manuscript) * quad - unique,
 within-in site identifier for each permanent 1m<sup>2</sup>
 quadrat * pl.height - height of measured purple loosestrife stem in cm *
 pl.fertile - whether the measured stem had an inflorescence *
 pl.number.inflor - the total number of inflorescences on the measured stem
 * pl.inflorescence.length - the length of the longest inflorescence (in
 cm) on the measured stem * pl.number.flowers - the number of individual
 flowers in the middle 5 cm of the longest inflorescence. Note: if
 inflorescence was &lt;5cm, all flowers were counted. * notes - pertinent
 notes pertaining to that row of data * latitude - latitude of site in
 decimal degrees * longitude - longitude of site in decimal degrees *
 initial.density - the number of purple loosestrife stems within the
 permanent 1m<sup>2</sup> quadrat the first year of sampling
 (coincided with the year insects were first released at that site or [for
 the 'control' sites at Montezuma] the years insects were first
 released at neighboring sites) #### formatted.plquad * database.row - the
 order of the rows in the original, unformatted dataset * area - region of
 state where site was located (we sampled four regions: 'hudson'
 [Hudson River Valley, NY], 'mont' [Montezuma, NY],
 'tnc' [Western New York sites under stewardship of The Nature
 Conservancy], and 'west' [Western Lake Ontario sites in NY]) *
 site - name of sampled site (i.e., unique site identifier) * trt - which
 insects were intentionally released as part of purple loosestrife
 biocontrol program (four treatments: control = no insects were released,
 gal = only *Galerucella* sp. were released, gal.hyl = both *Galerucella*
 sp. and *Hylobius transversovittatus* were released, gal.hyl.nan =
 *Galerucella* sp., *Hylobius transversovittatus*, and *Nanophyes
 marmoratus* were all released [note: this only applies to one site], hyl =
 only *Hylobius transversovittatus* were released) * quad - unique,
 within-in site identifier for each permanent 1m<sup>2</sup>
 quadrat * month - month of data collection (either 'June' for
 summer monitoring of insects or ‘Sept’ for fall monitoring of plants) *
 date of insect release - first year insects were released at the site *
 year - the year the data was collected * num.years.after.release - the
 number of years between the first year insects were released at the site
 and the year the data was collected * pl.density - number of purple
 loosestrife stems per permanent 1m<sup>2</sup> quadrat *
 num.infl - total number of inflorescences produced by all purple
 loosestrife stems within the permanent 1m<sup>2</sup> quadrat
 * pl.damage - estimated percent of foliage removed by *Galerucella* sp.
 feeding (note: this data was collected in the Spring only, and was
 estimated as 0, 5%, 10%, or in similar 5% increments thereafter) *
 gal.eggs.actual.count - the number of *Galerucella* sp. eggs observed in a
 1-minute screening of the permanent 1m<sup>2</sup> quadrat *
 gal.eggs.categorical - the number of *Galerucella* adults observed in a
 1-minute screening of the permanent 1m<sup>2</sup> quadrat
 (estimated in categorical 'bins', with 5, 55, 300, 750, and 1500
 representing the midpoint of each category) * gal.larvae - number of
 *Galerucella* sp. larvae observed in a 1-minute screening of the permanent
 1m<sup>2</sup> quadrat * gal.larvae.presence - binary measure
 of whether or not any *Galerucella* larvae were observed in a 1-minute
 screening of the permanent 1m<sup>2</sup> quadrat * gal.
 adults - the number of *Galerucella* sp. adults observed in a 1-minute
 screening of the permanent 1m<sup>2</sup> quadrat *
 water.cover - the percent of the permanent 1m<sup>2</sup>
 quadrat covered in water (note: the sum of the values in water.cover,
 litter.cover, and soil.cover should equal 100) * litter.cover - the
 percent of the permanent 1m<sup>2</sup> quadrat covered in
 litter (note: the sum of the values in water.cover, litter.cover, and
 soil.cover should equal 100) * soil.cover - the percent of the permanent
 1m<sup>2</sup> quadrat where bare soil is visible (note: the
 sum of the values in water.cover, litter.cover, and soil.cover should
 equal 100) * water.depth - the average of the water depth (in cm) measured
 at each of the four corners of the permanent 1m<sup>2</sup>
 quadrat * litter.depth - the average of the litter depth (in cm) measured
 at each of the four corners of the permanent 1m<sup>2</sup>
 quadrat * vertical.cover - lowest number (0.5 dm) seen on a 4"-wide
 board held vertically; observed from 4m distant from the board *
 forb.cover - percent cover of forbs (excluding purple loosestrife) in
 permanent 1m<sup>2</sup> quadrats (note: estimated in large
 categories at Montezuma) * gram.cover - percent cover of graminoids
 (excluding purple loosestrife) in permanent 1m<sup>2</sup>
 quadrats (note: estimated in large categories at Montezuma) * ld.cover -
 total estimated percent cover of all forbs and graminoids in permanent
 1m<sup>2</sup> quadrats (note: not used in the analyses -
 highest number is 100) * veg.cover.by.species - sum of each percent cover
 for estimated for each species (note: sum may exceed 100) *
 num.species.with.pl - number of species in permanent
 1m<sup>2</sup> quadrat (including purple loosestrife) *
 typha.cover - percent cover of **Typha angustifolia** within the permanent
 1m<sup>2</sup> quadrat (categories included: 0 [no **Typha
 angustifolia**], 3 [&lt;5% **Typha angustifolia**], 10 [5-15% **Typha
 angustifolia**], and 10% increments thereafter) * typha.density - the
 number of **Typha angustifolia** stems within the permanent
 1m<sup>2</sup> quadrat * initial.density - the number of
 purple loosestrife stems within the permanent 1m<sup>2</sup>
 quadrat the first year of sampling (coincided with the year insects were
 first released at that site or [for the 'control' sites at
 Montezuma] the years insects were first released at neighboring sites) *
 latitude - latitude of site in decimal degrees * longitude - longitude of
 site in decimal degrees * presence - whether or not purple loosestrife was
 present in permanent 1m<sup>2</sup> quadrat ####
 Loosestrife\_Decimal\_Degrees\_GPS\_Coordinates.csv * area - region of
 state where site was located (we sampled four regions: 'hudson'
 [Hudson River Valley, NY], 'mont' [Montezuma, NY],
 'tnc' [Western New York sites under stewardship of The Nature
 Conservancy], and 'west' [Western Lake Ontario sites in NY]) *
 site - name of sampled site (i.e., unique site identifier) * latitude -
 latitude of site in decimal degrees * longitude - longitude of site in
 decimal degrees * insect treatment - which insects were intentionally
 released as part of purple loosestrife biocontrol program (four
 treatments: control = no insects were released, gal = only *Galerucella*
 sp. were released, gal.hyl = both *Galerucella* sp. and *Hylobius
 transversovittatus* were released, gal.hyl.nan = *Galerucella* sp.,
 *Hylobius transversovittatus*, and *Nanophyes marmoratus* were all
 released [note: this only applies to one site], hyl = only *Hylobius
 transversovittatus* were released) ## Code/Software We used R to run the
 included scripts for data analyses. ### Brief explanation of R scripts
 related to analyses In order of how they are presented in Table 1 in the
 associated manuscript: * GAM.presence.R - model selection approach of
 models fit to data of **occupancy** (i.e., whether or not purple
 loosestrife was present or not within monitored quadrats) over time *
 GAM.pl.density.negative.binomial.R - for quadrats where purple loosestrife
 was present, this script includes the model selection approach for models
 fit to data of purple loosestrife **stem density** over time *
 GAM.five.tallest.height - for data of five tallest stems within each
 quadrat, this script includes the model selection approach for models fit
 to data of purple loosestrife **stem height** over time * GAM.fertile.R -
 for data of five tallest stems within each quadrat, this script includes
 the model selection approach for models fit to data of **proportion of
 fertile** stems over time * GAM.numinflorescences.R - for data of five
 tallest stems with each quadrat, this script includes the model selection
 approach for models fit to data of **number of inflorescences** over time
 * GAM.5.tallest.inflor.length - for data of five tallest stems with each
 quadrat, this script includes the model selection approach for models fit
 to data of **inflorescence length** over time * GAM.number.of.flowers.R -
 for data of five tallest stems within each quadrat, this script includes
 the model selection approach for models fit to data of **flower density**
 over time *Note: more detailed explanations of the response variables are
 available in the preceding column descriptions section and in the
 associated manuscript*