Distribution And Classification Of Aquatic Weevils (Coleoptera : Curculionidae) In The Genus Euhrychiopsis In Washington State

10 Pages·1999·3.4 MB·English

by  M Tamayo

Vol. 110,No. 2,March&April, 1999 103
DISTRIBUTION AND CLASSIFICATION OFAQUATIC
WEEVILS (COLEOPTERA: CURCULIONIDAE) IN THE
GENUS EUHRYCHIOPSIS IN WASHINGTON STATE1
MarianaTamayo2,Charles\V.O'Brien3,RobertP.CreedJr.4,ChristianE.Grue2,
KathyHamel5
ABSTRACT: During the summers of 1993, 1996 and 1997, we surveyed a total of66 sites in
WashingtonStatetodeterminethepresenceanddistributionoftheaquatic weevil Euhrychiopsis
lecontei.E.leconteiwasfoundin8sitesin 1993,allineasternWashington.In 1996theweevilwas
foundin9lakes,2ofwhichwherelocatedinwesternWashington.During 1997,wefoundweevils
in 14 sites, all except one were located east ofthe Cascade Mountains. Previously, the genus
Euhrychiopsiswasconsideredtohave2species,leconteiandalbertanus.However,examinationof
themalegenitaliafromspecimensofbothspeciesinthisgenusfrom20populationsacrossNorth
Americashowednodifferenceswithinorbetweenpopulations.Therefore,thereisonlyonevalid
species in the genus Euhrychiopsis, namely lecontei. E. albertanus is ajunior synonym [NEW
SYNONYMY].
Inrecentyears, the aquatic weevil Euhrychiopsis lecontei (Dietz) has been
receivingagreatdealofattentionfrombothresearchersandresourcemanagers
asapotential biological control agentofEurasianwatermilfoil (Myriophyllum
spicatumL.),anaquaticmacrophytenativetoEurope,AsiaandnorthernAfrica
(CouchandNelson 1986).Thisweevil isnativetoNorthAmericaandhasbeen
associated with declines ofM. spicatum in the continent (Creed and Sheldon
1995,Lillie 1996,Jesteretal. 1997,Creed 1998).Inaddition,mostoftheunex-
plained declines of M. spicatum in North America have occurred within E.
lecontei's original range (Creed 1998). Laboratory and field studiesconducted
in Vermont and Minnesota have concluded that this weevil is a watermilfoil
specialist and that itcanhave anegative impacton Eurasian watermilfoil (e.g.
CreedandSheldon 1995,SheldonandCreed 1995,Newmanetal. 1996,Solarz
and Newman 1996).
Given the promising results seen in Vermont and Minnesota and that Eur-
asian watermilfoil is currently found in 86 lakes and rivers throughout Wash-
ington State (Parsons 1997), E. leconteimay be an alternative forcontrolling
1 ReceivedApril30, 1998.AcceptedJuly4, 1998.
2 Washington Cooperative Fish and Wildlife Research Unit, School ofFisheries, University of
Washington,Box357980,Seattle,WA98195-7980USA.CorrespondencetoM.Tamayo.
- Entomology-BiologicalControl,DivisionofAgriculturalSciences,CollegeofEngineeringSci-
ences,TechnologyandAgriculture,FloridaA&MUniversity,Tallahassee,FL32307-4100USA.
4DepartmentofBiology,AppalachianStateUniversity,Boone,NC28608USA.
^WaterQualityAssistanceProgram,WashingtonDepartmentofEcology,P.O.Box47600,Olym-
WA98504USA.
pia,
ENT.NEWS 110(2) 103-112,March&April, 1999
04 ENTOMOLOGICALNEWS
1
Eurasianwatermilfoil inthisstate. However,severalquestionsaboutthedistri-
bution ofE. lecontei need to be determined before implementing a biological
control program thatusesthisweevil inWashington State. Priortoourstudy, it
wasnotknown ifthe weeviloccurredthroughoutWashingtonorwaslimited to
certain regions. Forexample, ifthe weevil is present only in easternWashing-
ton it may not be possible to use it as abiological control agent in the western
part of the state. We were also interested in determining which watermilfoil
speciesare servingashostplantsforE. lecontei. In additiontodeterminingthe
geographic distribution and host plant usage ofE. lecontei in Washington, we
alsoresolvedtheconfusion thatexistedwithregardstothe taxonomy andclas-
sification of weevils in the genus Euhrychiopsis. Dietz erected this genus in
1896asasubgenusofPhytobiusSchoenherrandbased ituponasinglespecies,
leconteiDietz.Subsequently in 1932,Brownaddedasecondspecies,albertanus
tothegenusPhytobius.BrownconsideredE. leconteitobeajuniorsynonymof
theEuropeanEubrychiusvelatusBeck,followingtheconsensusofotherAmeri-
can weevil specialists. Buchanan (1937) corrected this error and pointed out
that Eubrychius was restricted to Europe. Aprevious examination by the sec-
ond author (CWOB), of specimens identified as Eubrychius from numerous
museums inthe United States,showedthatall suchNorthAmericanspecimens
weremisidentifiedEuhrychiopsislecontei.InColonnelli's(1986)WorldCheck-
list of Phytobiini, Eubrychius was considered to be Holarctic. However,
Colonnelli did not list any actual localities in the United States or Canada. In
addition, he recognized Euhrychiopsis as having two species, lecontei and
albertanus. This classification was based on differences in coloration, but it
was unclear if these were two separate species or only one. To determine if
CWOB
thesecolordifferences are indicativeoftwospecies, examined numer-
ous individuals from across North America within the genus Euhrychiopsis,
including those collected in the present study.
METHODS
1993 Surveys
The third author (RPC) surveyed 20 lake and riverine sites in Washington
forEuhrychiopsis.Threeofthe20siteswerelocatedwestoftheCascadeMoun-
tains and 17 were in eastern Washington. Surveys were conducted in late July
andearlyAugustandspecimenswerecollectedbyeitherwadingorsnorkeling.
Eurasianandnorthern watermilfoil (M. sibiricum Komarov = M. exalbescens
Fernald)wereexaminedforadultweevilsandlarvaldamage.Watermilfoilspe-
cies were distinguishedby morphological differences (Aikenetal. 1979). Lar-
val damage,unique toE. lecontei, was identifiedbyexamining plantstemsfor
holes and burrowing created by late instar larvae (Creed and Sheldon 1994a,
1995; SheldonandO'Bryan 1996a;Jesteretal. 1997). Sitesinadditiontothose
listed inTable 1 were visited, but no attempt was made tocollectat these sites
Vol. 110,No. 2,March&April, 1999 105
as no watermilfoil was observed from shore.
1996-97 Surveys
Thirty-seven lakes (2 from 1993, Lakes Pateros and Curlew) and a section
ofthe Columbia Riverby the city ofMaryhill were surveyed frommid-July to
theendofAugust, 1996. In 1997, 37 ofthese sitesandanadditional 13 (3 from
1993,OkanoganRiveratOroville,WhitestoneLake,andtheColumbiaRiverat
Brewster) were surveyed from early June to early September. Aquatic plant
data previously collated by Sharon Walton (1996) and Jenifer Parsons (1997)
wereusedtoselectsurveysiteseachyear.Basedontheirdata,mostsitesvisited
were reported previously to have either Eurasian and/or native northern
watermilfoil. We tried to avoid sites where Eurasian watermilfoil was being
controlled asthiscanreduce weevil abundance (SheldonandO'Bryan 1996b).
Of the 38 sites we visited in 1996, 16 were located in western Washington,
while the remaining 22 were east of the Cascades. In 1997, 24 sites were in
westernWashington and 26 were eastofthe Cascades (Table 1).
We surveyed the shoreline of each lake and river site to locate and map
watermilfoilbeds.Wheneverpossible,5 locations withinthe watermilfoil beds
(monotypicand/ormixedspecies, includingplantsotherthanwatermilfoils)of
each waterbody were selected randomly in 1996. These same locations were
surveyed again in 1997. If we did not find any watermilfoil in a location in
1997, we selected anew one randomly. Three snorkel surveys wereconducted
ineachofthe 5locationsinbothyears.Each surveyconsistedofsnorkelingfor
m
5 minutes, examining the top 0.50 ofwatermilfoil plants for adult weevils
and larval damage; this is the same method used inVermont(H. Crosson,Ver-
montDepartmentofEnvironmentalConservation,Waterbury,VT,pers.comm.).
Any adults that were found were collected and larval damage observed was
recorded. Representative samplesoflarval damage werecollected in 1996 and
1997. If the survey site consisted of a mixed species bed, plants other than
watermilfoilswere briefly checked;howeveroursurveysfocusedprimarilyon
watermilfoil species.
Twoplantspecimenswerecollectedateachwatermilfoilsurvey site within
each waterbody. One plant sample from each site was pressed, while the other
specimen was identified. Since mostofthe collected plants did nothave flow-
ers,differentiationofthe watermilfoil specieswasbasedon stem andleafmor-
phology(Aikenetal. 1979). Iftheclassificationofanyspecimenwasuncertain
the plants were identified only togenus.
WeevilClassification
Duringall 3 surveyyears,adultweevilswerecollected when foundand the
plants they were associated with were noted. Voucher specimens were depos-
ited in CWOB's collection, at the School ofFisheries, University ofWashing-
106 ENTOMOLOGICALNEWS
ton, Seattle, WA and in RPC's personal collection. To determine ifthe genus
Euhrychiopsistrulyconsistsof2species,leconteiDietzandalbertanusBrown,
CWOB compared the coloration and morphology (male genitalia) ofthe wee-
vilswecollectedtothatofweevilsofthe same genusfrommorethan 20popu-
lationsfromCanada(Alberta,Saskatchewan,BritishColumbia)andtheUnited
States (MN,WA,WI, UT,VT,IA, CO, and IL).
RESULTS AND DISCUSSION
Classification
Based on close examination ofnumerous specimens ofE. lecontei and E.
albertanusbyCWOB,thereisonlyonevalidspeciesinthegenusEuhrychiopsis,
namely lecontei Dietz. E. albertanus Brown is ajunior synonym ofthe latter
[newsynonymy].Dissectionsofmalegenitaliashowedthattherearenodiffer-
enceswithinorbetweenpopulations.Thespecimensexaminedrepresentasingle
specieswithawiderangeofcolorformswhichvary sogreatlythattheyshould
notbe treated even as subspecies. In fact, multiple colorforms have been col-
lected within the same waterbody in at least Washington and Wisconsin (R.
Lillie,WisconsinDepartmentofNaturalResources,Monona,WI;pers.comm.).
Consequently, any specimens which key to Euhrychiopsis using Colonnelli's
key (1986) can be treated asE. leconteiDietz.
Typically, eastern NorthAmericanpopulationsofE. lecontei are distinctly
mottled. Their dorsal surface ranges from pale yellowish brown to greenish
brown,mixed withdarkbrowntoblackmaculae and ayellowishventer. West-
ward populations tend to become darker in a clinal fashion, with the macula-
tionsbecominglargerandmorepredominant.TypicalE.albertanuswerenearly
blackwithadistinctwhitishpostcutellarsuturalvittaandawhitishventer.How-
ever, inall the seriesofalbertanusfrom the westernprairie (including the type
locality)thatwereexaminedby CWOB,darkmottledspecimensalsooccurred
in addition to black specimens. West ofthe Rocky Mountains in Washington
andBritishColumbia,darkmottledformsarepresent,andsofarnosolidblack
formshave been collected. Even though there is this greatcolorvariation, it is
clearthat this is a single species. Hence, Euhrychiopsis is a monotypic genus.
Thelatterisencouragingbecause futurecontrolefforts involvingweevilsfrom
this genus need only to focus onone species, leconteiDietz.
DistributionofE. lecontei
In 1993,wefoundE. lecontei in8ofthe 20sites surveyed; all siteswere in
eastern Washington. During the 1996 surveys, E. lecontei was present in 9 of
the 38 sites. Two ofthe lakes, Sawyer and Meridian, were located in western
Washington, while the other 7 were in eastern Washington. Only 2 of the 8
weevilsitesfrom 1993,LakePaterosandCurlewLake,weresurveyed in 1996.
Bothlarvaldamageand2adultswerecollectedinCurlewLakein 1996.Wedid
notfindeither in Lake Pateros, howeveronly a section ofthe eastern shore of
Vol. 110,No. 2,March&April, 1999 107
the lake was surveyed. In 1997, we found E. lecontei in 14ofthe 50 sites sur-
veyed. All sites except for Lake Sawyer were in eastern Washington. Only 3
weevil sites from 1993,LakePateros,Curlew Lake and the Okanogan Riverat
Oroville,weresurveyed in 1997.Wefound larvaldamageboth inCurlewLake
and the Okanogan River at Oroville, while in Lake Pateros we did not detect
any adults or larval damage. In addition, all ofthe weevil sites from 1996 had
larval damage and/or adults in 1997, except for Lake Meridian where neither
were detected.
To date, we have found E. lecontei in 21 lake and riverine sites around
Washington (Table 1). Most ofthese sites were located in eastern Washington
(19), howeverwe did findE. lecontei in westernWashington. Westofthe Cas-
cades, the weevil was present only in King County, in Lakes Meridian and
Sawyer.IneasternWashington,E. leconteioccurredin7counties,Chelan,Ferry,
Grant, Lincoln, Okanogan, Pend Oreille and Spokane. Only 3 of the 19 sites
with weevilseastoftheCascadeswere located inthe Columbiaand Okanogan
Rivers. We found the greatest number of adult weevils in Fish Lake (17) in
1996, followed by Sawyer Lake (9) in 1997. The presence of E. lecontei in
eastern and western Washington is promising, as this would facilitate future
biological control programs using this weevil in both regions. In addition, it is
encouragingthatwefoundE. leconteiintheColumbiaandOkanoganRiversas
well as in King County, because Eurasian watermilfoil is a nuisance in these
areas.Infact,theearliestherbariumspecimenofEurasianwatermilfoil inWash-
ingtonStatewascollectedfromLakeMeridianinthemid 1960's(Parsons 1997).
We also found that inWashington, E. lecontei is associated with both Eur-
asianandnorthernwatermilfoil(Table2),the latterbeingnativetothestateand
North America. To date, E. lecontei has been found primarily on Eurasian
watermilfoil inwesternWashington.Incontrast,ineasternWashingtonweevils
were found in more waterbodies with northern watermilfoil than Eurasian
watermilfoil. Northern watermilfoil is widely distributedthroughoutWashing-
ton, particularly east of the Cascades. In 11 of the 19 weevil sites in eastern
Washington, E. lecontei was associated with northern watermilfoil. Ofthe re-
maining 8 weevil sites in eastern Washington, weevils were present on Eur-
asian watermilfoil in 6 (Lake Pateros, SacheenLake, Evergreen Lake, Colum-
bia River at Entiat, Okanogan River at Oroville and below Lake Osoyoos),
while in the other2 sites (Aeneas and Stan Coffin Lakes) E. leconteioccurred
on both Eurasian and northern watermilfoil. Because our surveys focused pri-
marily on watermilfoil species, we can notcommenton the host specificity of
E. lecontei. However, our data do provide further evidence that northern
watermilfoil is a native host ofE. lecontei. In at least 7 lakes with weevils, M.
sibiricum has been the only watermilfoil species present. Ourresults corrobo-
rate those ofCreed and Sheldon (1994b) who found E. lecontei in 1 lakes in
Alberta, Canada where Eurasian watermilfoil was absent, but northern
watermilfoil was present.
108 ENTOMOLOGICALNEWS
Vol. 110,No. 2,March&April, 1999 109
ENTOMOLOGICALNEWS
110
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Vol. 110,No. 2,March&April, 1999 111
There are several questions that still need to be answered before imple-
mentingabiologicalcontrol program withE. leconteiinWashington State. For
example, do differences exist in the life history ofE. lecontei in eastern and
westernWashingtonsincebothregionshaveverydifferentclimaticconditions?
Most, if not all of the lakes in eastern Washington where weevils have been
collectedfreezeduringthe winter; this isnotthecase forthe lakeswith weevils
inwesternWashington.Also,doesthe weevil interactwithothernative species
ofwatermilfoil inWashington?We are uncertain ifnorthern watermilfoil is the
only nativeplantthat isahostforE. lecontei inWashington. Inaddition,wedo
notknowwhatimpacttheweevil mayhaveonothernativewatermilfoilsfound
in the state, such as western (M. hippuroides Nuttall) and whorled (M.
verticillatumL.)watermilfoils.Finally,howdoweevil densitiesinWashington
State compare with those ofotherstates whereE. leconteihas been associated
with declines ofEurasian watermilfoil (e.g., Illinois, Vermont, and Wisconsin
[Jesteret al. 1997])? The "low" numbers ofweevils collected in our study do
notnecessarily implylowweevildensities.Similarly,thefactthatweevilswere
notfound inmostofthewaterbodies surveyed(60% in 1993,76% in 1996 and
%
72 in 1997) does not necessarily indicate that weevils are not presentthere.
Local areas where weevils were presentmay nothave been surveyed. In addi-
tion, lakes may have been surveyed too early or too late in the season, thus
missing peak weevil densities.
Table2. Number(%)oflakessurveyedinWashingtonStatewithEuhrychiopsisleconteiandthe
watermilfoilspeciespresent.'
EasternWashington WesternWashington
No.ofwaterbodiessurveyed
112 ENTOMOLOGICALNEWS
WaterQualityAssistanceProgramthroughtheWashingtonCooperativeFishandWildlifeResearch
Unit. C.E.Grueisemployedbythe Biological Resources Divisionofthe USGS andthe Unitis
supportedbytheUSGS,theUniversityofWashington,andtheWashingtonDepartmentsofEcol-
ogy, Fish and Wildlife, and Natural Resources. Research by CWOB was funded in part by the
USDA'sCooperativeStateResearch,Education,andExtensionService(FLAX910001).Surveys
conductedby RFC in 1993 were fundedinpartbythe USArmyCorpsofEngineers'Waterways
ExperimentStationinVicksburg,MS.RFCwasalsosupportedbytheUSEnvironmental Protec-
tionAgency,theVermontDepartmentofEnvironmentalConservationandMiddleburyCollege.
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