Occurence of alderfly larvae (Megaloptera) in a West Virginia population of the purple pitcher plant Sarracenia purpurea L. (Sarraceniaceae)

4 Pages·1996·1.4 MB·

by  J L Pittman

Vol. 107,No.3,May&June, 1996 137
OCCURRENCE OF ALDERFLY LARVAE
(MEGALOPTERA) IN A WEST VIRGINIA
POPULATION OF THE PURPLE PITCHER PLANT,
SARRACENIA PURPUREA L. (SARRACENIACEAE)1
J.L. Pittman,2T.S.Turner,2 L.Frederick,2 R.L.Petersen,2 M. E. Poston,2
M. Mackenzie,3 R. M.Duffield2'4
ABSTRACT:Eightalderfly(Sialidae)larvaewereidentifiedinthecontentsof99leavescollected
May 14-15, 1994, fromapopulation ofthe purple pitcherplant,Sarraceniapurpurea, from Big
RunBog,TuckerCounty,WestVirginia.Fiveofthelarvaeweresurroundedbymyceliamats.The
fungus belonged to the water mold genus, Sapmlegnia (Saprolegniaceae). Adult alderflies col-
lectedfromthesamelocalityinJuneweredeterminedtobeSialisjoppa.Theoccurrenceofalderfly
larvaeinpitcherplantsisunusual,andprobablyrelatedtofloodingofthehabitat.
Alderflies(Sialidae)areasmallfamilyofaquaticinsectswithapproximately
23 North American species (Evans, 1984). The predacious aquatic larvae can
be abundant in streams, rivers and ponds. Larvae migrate from the water and
pupateon dry ground several yards from the water. Adult insects are generally
found in the same areas as the immatures. They are usually inactive, resting in
thevegetationneartheirlarvalhabitats.InWestVirginia,fourspeciesofalderflies
have been reported (Tartaretal., 1973; 1978) .
While studying apopulation ofpurplepitcherplants, Sarraceniapurpurea
L, in West Virginia, the contents trapped at the base of several leaves were
analyzed by transferring the materials into separate petri dishes. One of the
leavescontained alarvaapproximately 1.0cmlong, which was lateridentified
as belonging to the genus Sialis (Sialidae). Astudy was initiated to determine
whethersialid larvae are common to this population ofpitcherplants.
This study is significantbecause itaddstoourknowledgeofthe biology of
pitcher plants. Although a variety of species of arthropods are known to be
regular inhabitants ofthese unusual carnivorous plants, it is not clear whether
sialid larvae areprey, occasional associates orregular inhabitants.
1 ReceivedOctober23, 1995;AcceptedNovember28, 1995.
2 DepartmentofBiology,Howard University,Washington,D.C.20059.
3UnitedStatesDepartmWenVtofAgriculture,ForestService,Forest-HealthProtection, 180Canfield
Street,Morgantown, 26505.
4Towhomcorrespondenceshouldbesent.
ENT.NEWS 107(3): 137-140,May&June, 1996
138 ENTOMOLOGICALNEWS
METHODS
TheS.purpureaWpopulation is located in BigRun Bog located at39 07'N
latitudeand 79 35' longitude, TuckerCounty, WestVirginiaatanelevation
of 980 m above sea level. The bog occupies approximately 20-25 ha in the
MonongahelaNational Forest (Wiederetal. 1981). Big Run Bog (also known
asOlsonBog)isdominatedbySphagnumandPolytrichumwhichtogethercover
85% ofthe surface (Wiederetal. 1981). Sarraceniapurpurea was introduced
tothisbogin 1946(StrausbaughandCore, 1970)andiswellestablishedtoday.
On May 18, 1994 fourmatureplants werecollected forleafanalysis. Indi-
vidual plants were scooped up by hand,placed inplasticpans with water, cov-
eredandtransportedbacktothelaboratoryatBlackwaterFallsStatePark.Three
additional plants werecollectedJune 14-15, 1994.
During thetwo visits to the bog in 1994, adultinsects werecollected using
bothasweepnetandabeatingsheet.Inearlyspringofthenextyear(March30,
1995), aquatic specimens were collected using an aquatic insect net from the
shallow waterin the same vicinity where thepitcherplants had been collected
previously. Specimens werepreserved in 70% ethanol.
Individualleaveswereanalyzedafterremovalfromthemainclusterbycut-
tingthebasewitharazorblade.Liquidcontentsofeachleafwerepouredintoa
watch glass. The leafwas then slitlengthwiseand folded open. The solidcon-
tents at the base ofthe leafwere removed with a spatula and placed in a vial
containing 70% ethanol. Ninety-nine leaves wereprocessed from theMay 20,
1994 collections and an additional forty-seven leaves from the June 14, 1994
collections. Each sample was examined under low magnification and alderfly
larvae wereremovedandplaced in separate vials.
RESULTS
A
total ofeightalderflylarvaewereidentifiedin thecontentsofthe leaves.
All larvae wererecoveredfrom theMay collections; none wasrecoveredfrom
theJunecollections. Eachoftheplants sampled in May had atleastonelarvae
in a leaf sample. Microscopic examination revealed dense mycelial growths
attached tothemembranousareasofthe larvae.Thefungus was identified asa
species ofSaprolegnia, a true watermold (Saprolegniaceae) (Coker, 1923).
Although no adult alderflies were collected in May from the sweep netor
beatingsheetsamples, several werecollectedinJuneincludingoneadultmale.
The specimen was identified as Sialisjoppa Ross. Four species of alderflies
have been recorded inWestVirginiaincludingS.joppa (Tartaretal., 1978).
Vol. 107,No.3,May&June, 1996 139
DISCUSSION
Pitcher plants are usually associated with bogs or swamps and are rather
unusual becausethey exhibitpassivecarnivory.Anumberofreportsdocument
that S. purpurea capture a broad spectrum of insect species as well as other
arthropods (Rymal and Folkerts, 1982; Bradshaw and Creelman, 1984). Spe-
cies found in the pitcher plant may be classified as inhabitants, prey, pitcher
plant herbivores or occasional associates. Purplish/red nectar guides lead
attracted insects up the brightly colored leaves to the lip where some ofthem
fall into the water-filled reservoir below (Joel, 1986). Pitcher plants rely on a
diversecommunityofbacteria,protozoaandinsectlarvaefordecompositionof
trapped prey and absorption ofnutrients (Addicott, 1974).
Alderflylarvaehavepreviouslybeenrecoveredfrompitcherplants. Mather
(1981) recovered S. joppa larvae from a population of S. purpurea in New
Jersey, one in late April and the other May 30. The collection dates for our
material coincide well with the New Jersey collections. No fungal growth on
the specimens was reported by Mather. There also was no indication of the
numberofplants sampled.
The presence ofeight sialid larvae in 99 leafcontent samples shows that
sialid larvae are relatively common insects found in this population ofpitcher
plants. Since the same species has now been found in two widely dispersed
pitcher plant populations, it may be inferred that they are not rare in pitcher
plants. Whether sialid larvae are prey is notclear. Five ofthe larvae exhibited
dense growths ofSaprolegnia indicating the specimens were dead when col-
lected. It is not known whether the other two larvae were alive or dead at the
time ofcollection.
Alderfliesaregenerallyassociatedwithbothloticandlentichabitats.Mather
(1981) suggestedthatthelarvaemayhaveenteredthepitcherplant insearchof
pupation sites. We suggest that in early spring the water level in the bog is
higherdue to both snow meltandrain. During thattime sialid larvaedistribute
throughoutthebog, somemoving intopitcherplant leaves where a rich source
ofdead insects and live Diptera larvae can provide nourishment. As the water
level recedes, the sialid larvae become stranded in the leaves. In March, 1995,
weattemptedtotestthishypothesisbycollectingaquaticinsectsfromtheshallow
waterinthevicinityofwherepreviouspitcherplantcollectionshadbeenmade.
No sialid larvae wererecovered.
Milesetai, (1975)reportedthatarelatedpitcherplantspecies, Sarracenia
flava, producesanumberofnaturalproductsincludingtwoamines, an unusual
enol diacetal monoterpene, sarracenin, andconiine, oneofthe poisonous alka-
loids found in hemlock (Conium maculatum). The two amines are responsible
forparalyzing insects afterthey become entrapped in the pitcher.
Itispossiblethatconiine, sarracenin,orothertoxicaminesarepresentinS.
purpurea. Theseorrelatedcompoundsmay immobilizeorkill sialid larvaethat
140 ENTOMOLOGICALNEWS
enter the pitcher plants. The dead insects may subsequently be invaded by a
species ofSaprolegnia which decomposes the larvae, providing nutrients for
theplant.
ACKNOWLEDGMENTS
ThisstudywasaresultofasummerForest BiologyandEcology FieldCoursesponsoredby
theU.S.D.A.-ForestService(EasternRegion)throughamemorandumofunderstandingwithHoward
University.WethankBillWoodland,DistrictRanger,CheatDistrict,MonongahelaNationalForest
forthecoordinationandlogisticalsupportofthefieldcourseandMaryBethAdams(ProjectLeader,
SustainableForestEcologyInCentralAppalachianForests)forassistingwithteachinginthefield
course.EcologicalReport#2.
Wewould liketothankOliverS. FlintJr. (DepartmentofEntomology, Smithsonian Institu-
tion,Washington,D.C.)fortheidentificationoftheadultalderfly.
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