Table Of ContentVol. 107,No.3,May&June, 1996 169
SAMPLING TECHNIQUE FOR
SOIL MACROARTHROPODS
INHABITING FOREST FLOORS1
PierrePaquin,DanielCoderre^
ABSTRACT: Mostsoilfaunasamplingtechniqueshavebeendevelopedformicroarthropodsand
arenotsuitable forsamplingmacroarthropods.Thispaperdescribesabettersampling methodol-
ogy fortheentire macroarthropodsassemblage.Agiven sampleareaof 12.5cmby25cmexempt
frombiasesandobstaclesisdividedintothreefractions(aerial,epigeicandendogeic).Thecollec-
tionofeachfractionisadaptedtothebehaviorofthesoilfaunathatitcontains.Flyinginsectsare
firstcollectedwitharemovablenetattachedtothetopedgeofthesamplingmold,thelitteristhen
gathered by hand, and finally the deeper organic layers are collected in a block. This method
permits sampling ofthe soil by taking into consideration the vertical distribution oforganisms.
Samplesstoredasblocksofsoilinpolyethylenebagsaresufficientlylargeandstabletoinsurethe
survival oforganisms until extraction. This new methodology has certain advantages overtradi-
tional methods in that it allows aquantitative sampling ofall soil organisms according to their
verticaldistribution.
Most sampling techniques for soil fauna have been developed by taking
into consideration the microdistribution, small size and high density ofmicro-
arthropods (especially Collembola and Acarina). These sampling parameters
are not suitable for macroarthropods which are, in general, less numerous per
unit area (Edwards 1967). The dimensions of the sample must therefore be
proportional tothesizeoftheorganisms (Kaczmarek 1993), whereasthe shape
mustattempttomaximizetherepresentationofthesoil understudy. Indeed,the
number ofsamples and the sample volume itselfmust attempt to compensate,
through sufficient volume and number, the potentially contagious distribution
ofedaphic organisms (Gorny and Griim 1993, Huflejtand Karwowski 1993).
Good sampling must be representative of the environment under study
(Kasprzak 1993) and avoid biases caused by nonhomogeneous features ofthe
soil, which often harbor a particular fauna. FlogaYtis (1983) recommends that
stumps,dead woodandproximity totreesshouldbeavoidedby keepingacon-
stant minimal distance between these biases and the sample. Indeed, thesedis-
tinctivefeaturesofthesoil harbortheirowncharacteristicfaunaandaresources
ofcontaminationtobeavoidedduringsampling.Stumps(SmithandSears 1982),
dead wood (Teskey 1976), animal excrement (Peck 1991), and fungi (Pielou
andVerma 1968)aremicrohabitats tobeavoided. Random sampling in an area
exempt from biases and obstacles is thus recommended for the study of soil
1ReceivedApril 11, 1995.Accepted May 14, 1995.
2UniversiteduQuebecaMontreal,GroupedeRechercheenEcologieForestiere,Departementdes
SciencesBiologiques,C. P.8888,Succ."A",Montreal,Quebec,H3C3P8.
ENT.NEWS 107(3): 169-176,May&June, 1996
170 ENTOMOLOGICALNEWS
organisms. Gorny and Griim (1993) suggest a flexible rather than a rigid
approach to sampling in respectofrandomly chosen plots. Goodjudgementis
thereforecalleduponwhendecidingwhethertoincludeorexcludehabitatchar-
acteristics during sampling. Forexample, old cedar forest soils are associated
withthepresenceofdecomposingwood(BergeronandDubuc 1989).Thisdis-
tinctivefeature should therefore be included in representative samples ofsuch
soils.
Geoffreyetal. (1981)andZukowski (1993)mentionthatadultDipteraand
Hymenoptera associated with the soil are rarely collected, even though these
insects play an important role in the dynamics in soil assemblage at the larval
stageorasparasitoidsorparasites(Zukowski 1993).Traditionalsamplingtech-
niques are not well suited for the characterization ofhighly mobile or flying
macroarthropods associated with the soil.
We believe thatthemethoddescribedhere is an improvementforthe sam-
pling and characterizationofsoil macroarthropods. Itisthebestpossiblecom-
promise given the numerous constraints and variables associated with the
collectingofsoilorganisms.Themethodhasproven itssuperiority inanexten-
sive forestsoil ecology samplingprogram.
MATERIALS
The equipment includes: (1)An aluminum sampling mold 6mm thick and
20cm high, witha 12.5cm by 25cm sampling surface (Fig. 1). Themold's bot-
A
tomedgeistaperedtoinsureagoodbiteintothesoil. (2) removableTerylene
net with an elastic band at its lower border(Fig. 1). This elastic bordercan be
adjustedtothetopedgeofthesamplingmold.ItshouldbenotedthattheTerylene
20cm
Elastic band
Figure 1.Samplingmoldandremovablenet.
Vol. 107,No. 3,May&June, 1996 171
can be replaced by another material transparent enough to allow visual local-
ization ofthe insects within the net. Terylene, however, is resistant to tearing
andisnotdegradedby light,asisthecasewithothermaterials.(3)Awashflask
filled with acetic alcohol. (4) Flexible tweezers. (5) Scintillation vials. Their
advantageis thatthey aremadeofunbreakableplastic. One vial isrequiredper
soil sample. (6)A knife with a long blade. (7)Asquare shovel. (8)A60cm by
90cm clean, white and smooth surface. A surface covered by melamine or
Formica is ideal. (9)Two-literpolyethylene bags. One bag persoil sample is
required. (10)Ten-literpolyethylenebags. Onebagpersoil sampleisrequired.
A
(11) measuring tape.
METHODOLOGY
This method was tested in boreal forests: including a deciduous forest
(PopulustremuloidesMichx.);amixedforest(Abiesbalsamea(L.)Mill.,Picea
glauca (Moench) Voss and Betulapapyri/era Marsh.); and a coniferous forest
(Thuya occidentalis L. andAbies balsamea (L.) Mill.). These forests are situ-
atedinwesternQuebec'sclaybelt, intheDuparquetLakeregion (4830'North,
79 15, West). SeeBergeron etal (1983) foramore detailed description ofthe
vegetation and soils in this region.
Ourtechniqueisaimedatquantifyingdiversityandbiomassatthreemacro-
arthropod groups: (1 ) flying adult insects associated with soils (Diptera and
Hymenoptera), (2) fast-moving epigeic insects in the litter (larval and adult
Staphylinidae, Carabidae,Arachnida, etc.) and (3) slowerendogeic organisms
found in the deeperorganic fraction (Diptera larvae, etc.).
The collection ofthe three fractions (aerial, epigeic and endogeic) consti-
tuting a sample is carried out in eleven distinct steps: (1) Sampling plots are
randomly chosen in areas exempt from biases and obstacles (as a function of
included and excluded characteristics). Walking heavily is avoided since soil
vibrations cause highly mobile insects to flee. (2)The sampling mold covered
by theremovable netis forcefullydriven intothesoil, sothatthetaperededges
ofthe mold penetrate the litter. (3)Afterone minute, the flying organisms can
be found in the net. They rarely numbermore than one or two at a time. (4)A
careful inspection allows one to locate and fix them using the wash flask filled
with acetic alcohol.Asinglejetofalcohol through the net is enough to immo-
bilize them. (5)Afterthe insects are immobilized, the net is removed. Because
ofthe surplus alcohol, the insects remain stuck on the innersurface ofthe net.
With the flexible tweezers, the insects are transfered to the scintillation vials.
This constitutes the aerial fraction ofthe sample. The vials must then be filled
with acetic alcohol and labeled according to the sample to which they belong.
(6) The litter (superficial layers composed of dead leaves, needles or twigs)
contained within the mold is then delicately gathered by hand. This litter is
transfered totwo-literpolyethylene bagsandconstitutes theepigeic fractionof
ENTOMOLOGICALNEWS
172
the sample. During the first steps oftheprocedure, because themold is driven
intothesoil, litterorganismsarepreventedfromescaping. (7)Theknifeisused
to cutthrough the soil along the inneredges ofthe sampling mold.The square
shovelcanbeusedtobreakrootsthattheknifecannotcut. (8)Themoldisthen
removed, afterwhich theblockofsoilislifted fromthegroundwiththesquare
shovelandplacedon theFormica board. (9)Theorganiclayersarethen sepa-
ratedfromthemineral layers soastotransferinoneblocktheorganiclayersto
the ten-literpolyethylene bags. This fraction constitutes theendogeic fraction
of the sample. In luvisols or podzols, the separation of organic layers from
mineral layersiseasilyaccomplished. (10)Thebagscontaininglitter,aswellas
theblocksoforganic layers,areplaced inan icechestuntil theycanbebrought
tothe laboratory. Caremustbe taken sothatthe blocks areplaced asthey were
originally found in the ground, with the top part of the blocks facing up, to
avoiddisturbingtheorganismstheycontain. (11)Thethicknessofthelitterand
ofthe organic layers are measured in the hole left after the samples are taken.
Thesedata will laterserve to calculate the volumeofeach fraction.
The total duration of the entire procedure in the field is ten minutes per
sample. In the laboratory, the contents ofthe scintillation vials are transfered
to vials that can better prevent the alcohol from evaporating. The fractions
4C
contained in the polyethylene bags are stored in a refrigerator at until
extraction.
DISCUSSION
We believe our methodology possesses many advantages over previously
used techniques. (1) Our approach for the choice of sample plots in areas
exempt from biases complements that ofFlogai'tis (1983). The elimination of
biases associated with nonhomogeneousdistinctive features ofthe soil insures
agreaterrepresentativity ofthe sample. Thegreatervolumecollected, in com-
parison with traditional soil core techniques (Vannier and Vidal 1965), results
in only slightly less flexibility regarding thechoice ofplots.
(2) Compared with the average small surface areas of samples generally
used in studies ofsoil fauna (Murphy 1958a, 1958b, Vannier and Vidal 1965,
Vannier 1966), that used in our method (312.5cm2) is 12.5 times larger. Be-
cause of its small size, traditional coring, aimed especially at Acarina and
Collembola, does notpermitatrueevaluationoflarger(andhence less numer-
ous per unit surface) macroarthropods (Edwards 1967). Vannier and Alpern
(1968), however, underline the fact that a sampling surface should correspond
to aprecise surface area. Thatproposed in ourmethodcorresponds to 1/32m2.
Vannier and Vidal (1965) recommend that the number rather than the size of
samples be increased; it ispreferable to have many smaller samples insteadof
one large sample. In that perspective, we are specifying that the sample size
Vol. 107,No.3,May&June, 1996 173
must respect the physical characteristics such as the distribution, the size and
the numberperunit areaofthe organisms understudy.
(3) The size ofthe sample proposed in ourtechnique approaches that used
by VannierandAlpern (1968), who adopted a20cm by 10cm surface, and that
by Flogai'tis (1983) with 25cm2. However, a rectangular rather than a square
shapewasadoptedbecause,foragivensurface,arectangularshapesampleson
a longer transect, which better distributes the sampling effort and tends to
reduce the influence ofacontagious distribution.
(4) Ourtechnique was tested in threetypesofforestsoils. Itisalsosuitable
for agricultural soils, as well as many other types ofecosystems. With respect
to its adaptability to different soil types, its versatility is comparable to the
traditional coring sampling techniques.
(5)Thevolumeofthesamplesandthemethodologydescribedhereinallow
the collection ofevery type ofsoil organism: flying organisms, organisms in
the litterand those fromdeeperlayers, be they macroormicroarthropods. Our
technique is nonselective, with each collected fraction adapted to the behavior
of the organisms that comprise that fraction. Collecting in three fractions
allowsarapiddeterminationoftheverticaldistributionoforganismsrelativeto
aprecise surfaceorvolume, withoutriskofcontamination, since ourapproach
eliminates migration of organisms from one soil layer to another due to the
layers' being collected separately. In general, traditional coring does not take
the vertical distribution oforganisms into consideration. Vannier and Alpern
(1968) propose a method, inspired by Murphy (1958a), to study the vertical
distribution oforganisms, but the small sampling area (20 cm2) of this tech-
nique is not suitable for macroarthropods. Our method, in this sense, comple-
mentsthatofFlogai'tis (1983)forthe separationofsublayersofthesample. No
othermethod allows the collecting offlying insects. With ourproposed meth-
odology, itispossibletosampleadultDipteraand Hymenoptera.Althoughcol-
lectedinlessernumbersthanbytheuseoftheterrestrialemergencecages(Martin
1977),thesespecimenscanfacilitatetheidentificationofimmaturestagesfound
in the soil, yield information on the phenology of the species
involvedandprovide thefirststep in associating parasitoids and parasites with
their hosts.
(6) Within a global approach to edaphic communities, our technique leads
to a large quantity of microarthropods (Acarina and Collembola) because of
their small size and the high densities they can reach (Edwards 1967). A sub-
samplingofthesegroups,oncethespecimensareextracted, isthereforerecom-
mended (Niedbala and Rajski 1993).
(7)Thequantitativeapproachofthistechniqueallowstheassociationofthe
organisms collected with a precise unit ofsurface or volume. The organisms
collected intheepigeicfractionarethesameasthosecollectedbytheEuropean
sifting technique described by Smetana (1971). The sifting technique is quali-
tatively moreefficientdue tothe large volumeoflitter it allowsone toprocess
ENTOMOLOGICALNEWS
174
The quantitative measure is however, more precise with a fixed soil surface
such as proposed by ourtechnique.
(8) Ourcollecting technique insures thatthe specimens are well preserved.
Theorganismsinthefirstfractionareplacedinalcoholwhileinthefieldandso
remain in aperfect condition. Those found in the litterare subjected to only a
delicatepressureduringthemanualcollecting,whichinsurestheirgoodcondi-
tion.Theorganismscontainedinthethirdfractionsustainonly aminimalpres-
sure during the cutting out ofthe block ofsoil. The large size ofthe samples
resultsintherebeinglittledisturbancefortheorganisms(Murphy 1958b,Vanier
andAlpern 1968).Traditionalcoring,becauseofthesmallsizeofthesamplesit
yields, exerts a physical pressure (Vannier and Alpern 1968) that can damage
fragile specimens.
(9) The technique of collecting soil samples in the shape of blocks was
initially proposed by Murphy (1958b) but the aim of his proposition was to
latersampletheblocksbycarefulcoringwithoutpressure. Ourtechniqueleads
to larvae samples andrequiresmore time forextraction than the smallertradi-
tional samples. Edward and Fletcher (1970) and Leinnas (1978) studied the
effects ofstorage on small samples. These were determined negligible forde-
laysof28 to 29 days. RapoportandOros (1969) reported variableeffectsfora
delay of 120days. They also showed that the useofpolyethylene bags (rather
than othermaterials) minimizes biases due to storage. Samples collected with
ourtechnique(intheshapeofblocksandstoredatlowtemperaturesinpolyeth-
ylenebags) allowanequivalentdurationofstorage, andprobably alongerone
becauseofthelargevolumeinvolved.Theseblockscreateatemporaryenviron-
ment sufficiently large and stable to insure the survival ofthe organisms they
contain. A low refrigerator temperature (4C) minimizes organism activity.
Maturationisnegligibleandreproductionofmostmacroarthropodsrequiresan
adultsexualphaseimpossibleundersuchconditions.Thelowlevelsofactivity
byindividualsandthelargesamplevolumeminimizepredationduringstorage.
Theproposedtechniqueis aimedmainlyatforestsoil macroarthropodsbut
isequally suitableforall edaphicorganisms. Ourmethod allows thecollection
ofindividualsbelongingtotheaerial,epigeicandendogeicfractionsofthesoil.
This quantitative method also considers the vertical distribution oforganisms.
The method is simple, inexpensive, efficient and rapid. It lends itselfto many
types ofbiological studies such as inventories, environmental impact evalua-
tions,parasitism,voltinism,microhabitatstudiesandtheverticaldistributionof
the soil fauna.
ACKNOWLEDGMENTS
TheprojectwassupportedbyagrantfromtheMinisteredeI'Enseignementsupe"rieuretdela
ScienceduQuebec(FCAR)toD.Coderre.WethankFernandTherrienforhelpinthefield,Laurent
LeSage,YvesBergeron,andtwoexternalreviewersforhelpfulcomments.
Vol. 107,No.3,May&June, 1996 175
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