a nestable fiber pot for sampling resting mosquitoes
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Journal of the American Mosquito Contol Association, ll(4):463467, 1995
Copynghi O 1995 by the American Mosquito Control Association, Inc'
A NESTABLE FIBER POT FOR SAMPLING RESTING MOSQUITOES
MCHOLAS KOMAR' RICHARD J. POLLACK eNo ANDREW SPIELMAN
Department of Tropical Public Healt|t, Haward School of Public Health,
665 Huntington Avenue, Boston, MA 02115
ABSTRACT To enhance the effectiveness of an arbovirus monitoring program, we evaluated a com-
mercially available device for sampling resting vector mosquitoes. Diverse Anopheles, Culiseta, and,Culex
mosquitoes were taken in these nlstable fiber pots. The pots sample about as many Culiseta melanura
mos{uitoes per device as do conventional resting boxes, but fewer than do boxes fitted with expanded
framis. Mori Cs, melnnura, and more bloodfed mosquitoes, but fewer species of mosquitoes are harvested
with fiber pots than with CDC light traps. Fiber pots are more readily used, transported, and stored and
are less expensive than conventional resting box devices or CDC light traps. A monitoring program based
on the use of fiber pots, therefore, expends fewer resources than one using conventional resting boxes
and collects about as many vector mosquitoes,
INTRODUCTION
Various kinds of devices have been used tocapture resting vector mosquitoes (Service
1976). Prt traps (Muirhead-Thomson 1958), bytheir nature, are placed permanently in a site andgenerally require elaborate construction. Wood-en kegs, once used for shipping nails, wereadapted for sampling anopheline mosquitoesduring World War tr (Smith 1942), and othermodifications on this theme have been usedsince. These resting box devices are open on oneside and generally are dark colored (Goodwin1942. Burbutis and Jobbins 1958. Gusciora1961, Moussa et al. 1966). Efficacy is enhancedwhen the apparent area of the opening is en-larged by mqrns of a funnel-like extension (Ed-man et al. 1968). These devices continue to beused in numerous malaria and arbovirus sur-veillance programs.
Although the efficacy and simplicity of thestandard rectangular resting box devices renderthem attractive for routine monitoring, their costand bulk impede their operational use. Becausenails no longer are packed in kegs, wooden rest-ing devices must be specially fabricated. Theirparallel-sided design, howevet prevents themfrom nesting and renders contained mosquitoesdifficult to harvest. A less expensive resting boxdevice that is more convenient to transport andeasier to use may facilitate efforts to monitormosquitoes.
To improve the efficiency of an ongoing ar-bovirus monitoring program, we evaluated theeffectiveness of commercially available, nesta-ble fiber pots for sampling natural populationsof Culiseta melanura (Coq.), a diurnally restingmosquito that is the enzootic vector of easternencephalitis (EE) and Highlands J viruses (Mor-ris 1988). Efficacy was compared among fiberpots, conventional plywood resting boxes, andCDC light traps.
MATERHLS AND METIIODS
Sampling devices: Commercially available fi-ber pots (Western Pulp Products Co., Corvallis,OR), are molded from recycled wood pulp in theform of hollow, truncated pyramids (Fig. 1) witha height of 28 cm. The base (open end) is 28 x28 cm, and the top (closed end) is 15 x 15 cm.The thickness of the fiber walls is I cm. Allsurfaces of the pot are dark brown.
For comparison, we used conventional ply-wood boxes (20 X 38 X 3O cm) fashioned fromplywood and with their interiors painted matteblack. Funnel-shaped entrance frames wereplaced on these boxes during part of the study(Fig. 2), effectively expanding the opening to 6OX 120 cm. Resting boxes and frames were pro-vided by John D. Edman, University of Massa-chusetts. Portable CDC miniature light traps(John W. Hock, Inc., Gainesville, FL) also wereused for comparison (Sudia and Chamberlain1962).
Study sites: Mosquitoes were sampled at 12sites in southeastern Massachusetts (Bristol,Plymouth, and Norfolk counties). Seven of thesesites were located in the Hockomock SwampWildlife Management Area, a location knownfor arbovirus activity, in the towns of Thuntonand Easton (Bristol County) and Bridgewater(Plymouth County). Three additional sites werelocated in Kingston (Plymouth County) and oneeach in Hingham (Plymouth County) andStoughton (Norfolk County). All sites appearedsuitable for capturing resting mosquitoes andwere near avian roosting sites.
Procedures: Fiber pots and resting boxeswere placed on the ground with their openingsoriented at random. Light traps were suspendedl-2 m above the ground at intervals ofabout l0m and operated overnight using 6-V motorcyclebatteries. Mosquitoes in light traps generallywere harvested during morning hours; resting
Frsen Pors ron Slt.,rpLwc ResrINc MoSQUIToES 465Decerrassn 1995
Table 1. Number of mosquitoes harvested in2,500 collections from nestable fiber pots set in
12 southeastern Massachusetts sites.
Mosquitoesper l,0OOcollections
Females
Species
7ablood- No.
No. fed males
Culiseta melanuraCuliseta morsitansAnopheles quadri-
maculatusCulex territansAedes cinereusCulex restuansCulex pipiensAno p he le s p unctip enni sUranotaenia sapphirinaCulex salinariusUnidentified
Total 51 294
to October 3, 1994 (Table 1). Culiseta melanurapredominated, comprising 75Vo of the harvest.Some Anopheles quadrimaculatus Say also wereharvested from these devices. More than half ofthe females harvested contained readily detect-able vertebrate blood. On average, about onemosquito was taken from each pot per day.Highlands J virus was detected in 2 of 95 poolsof pot-harvested Cs. melanura. Nestable fiberpots, therefore, sampled numerous vector mos-quitoes.
The harvest of mosquitoes taken in fiber potswas compared to that taken with conventionalplywood resting boxes and with resting boxesenhanced by an expanded frame. In Test I, 16fiber pots and 15 resting boxes were randomlyplaced within a 0.5-ha wooded space from Sep-tember 1 to September 17, 1994. A similar arrayof devices was monitored from July 18 to Au-glst 23, 1994, in Test II, except that expandedframes were placed on all resting boxes. Similarharvests of mosquitoes were recorded in the fi-ber pots and the frameless resting boxes (Table2). Boxes with expanded frames, however, har-vested far more mosquitoes than did the fiberpots. We conclude that fiber pots sample asmany mosquitoes as do resting boxes, but fewerthan do boxes fitted with expanded frames.
We then comp€ued the diversity of mosquitoestaken with flber pots to that taken with CDClight traps in Kingston, MA, from August 30 to
Table 2. Comparison of number of female
mosquitoes harvested from nestable fiber pots
with that from conventional resting boxes orresting boxes augmented by an expanded
frame.
Mosquitoesper l0O
collections
Culisetamelanura
No.col-lec-tions
48667
60 2063 1 0
3 2 43 2 r
1 9 069 <l62 l0 < l0 00 0o 4 l
2624
65J
2I
< 14
625
Collectiondevice
Totalno.
Voblood-
No. fed
24 132 t 2 l
13 2982 18
9590
u l96
II
Test
Fiber potResting box
Fiber potBox and frame
2830
l 6107
September 19, 1994. Twenty fiber pots wereplaced in a l-ha site near 6 light traps. This sitesupported the roosting of more than 1,000American robins (Turdus mi7ratorius Linn), butcontained no habitat suitable for larval Cs. me-lanura. More than twice as many female Cs. me-Ianura were taken per fiber pot than per lighttrap (Table 3). Our light trap collections includedmany more human-biting mosquitoes than didthe fiber pot collections; no Aedes mosquitoes,Coquillettidia perturbans (Walker), nor Culexsalinarius Coq. were taken in fiber pots. Al-though anopheline mosquitoes were taken withboth kinds ofdevices, light traps collected 3-foldmore than did fiber pots. Overall, more than 6times as many bloodfed mosquitoes were takenin fiber pots than in light traps. More Cs. me-lanura, and more bloodfed mosquitoes, but alesser diversity of mosquitoes, are harvestedwith fiber pots than with light traps.
DISCUSSION
Monitoring systems for vector mosquitoesmust be adapted to the peculiar features of thetarget mosquito and to the prevailing physicaland political environment. The nocturnal flightbehavior of Cs. melanura renders them vulner-able to capture in light traps, and their attractionto dark cavities results in their entry into artifi-cial diurnal resting devices. For various reasonsthe Encephalitis Surveillance Program of theCommonwealth of Massachusetts has beenbased on light trap collections (Edman et al.1993) and that of New Jersey on resting boxes(Crans 1994). A 3rd option, adopted by the stateof Florida, employs serological monitoring of
466 Jounxal or rne AunnrceN Mosqurro CoNrnol AssocterroN Vor . l l , No.4
Table 3. Comparison of number and feeding status of female mosquitoes harvested fromnestable fiber pots with that from CDC light traps.
Mosquitoes per 1,000 collections in
Fiber pots(260 collections)
Light traps(33 collections)
Species MeanVo
bloodfed MeanVo
bloodfed
Culiseta melanuraCuliseta morsitansAnop he I e s q uadrimac ul at u sCulex territansCulex restuansCulex pipiensU ranotae nia s ap p hirinaCulex salinariusAedes cantatorAedes vexansUnidentified
Total
9683o0
80loo
o
1799542I
< l000o
8 l6
1 80
l5J
J
369J
5
r79
2650o
20oo000o
152M 9 l
sentinel chicken flocks (Morris 1988). Eachsampling strategy produces data requiringunique modes of interpretation.
The fiber pots that we evaluated for monitor-ing Cs. melanura in Massachusetts may benefitencephalitis surveillance programs. As many Cs.melanura were harvested by means of theseconvenient and inexpensive devices as with theplywood resting boxes that have conventionallybeen used for this purpose. Although CDC lighttraps are said to collect about l0 times as manyfemale Cs. melanura as do resting boxes (Nascil98O'), we found that nestable fiber pots col-lected more mosquitoes than did unbaited CDClight traps. Larger collections of Cs. melanurafrom resting boxes than from CDC light traps atan upland farm site, but not in forested wetlandsites, have been reported (Joseph and Bickley1969). This finding may be explained by theabundance of vertebrate hosts at upland sites.Perhaps the attraction of a dense nidus of birdsoutcompetes the attraction of a light trap. Mos-quitoes seem to enter our pots most abundantlyearly in the afternoon, perhaps because they ini-tially rested postprandially in the canopy neartheir roosting avian hosts. Harsh daytime envi-ronmental conditions may drive these mosqui-toes toward the ground near our fiber pots. Therelative frequency of blood-engorged Cs. melan-rra distinguishes resting collections from light
'Nasci, R. S. 1980. Vector biology of Culiseta me-lanura (Coquillett) in southeastern Massachusetts.Ph.D. dissertation. Universitv of Massachusetts, Am-herst, MA. lfi) pp.
trap collections. A diversified monitoring pro-gram may be particularly useful because restingdevices sample a different segment of the vectorpopulation than do light traps.
The nearly total absence of Aedes mosquitoesin our fiber pot collections confirms observa-tions with other resting devices (Burbutis andJobbins 1958). The harvesting potential of fiberpots for Cq. perturbans, an important pest andpotential EE epidemic vector (Howitt et al.1949), has yet to be determined because thisspecies' adult population was exceedingly lowduring the period of study at our sites. Althoughfiber pots sample many more nocturnally activeCuliseta and Culex mosquitoes, light traps inMassachusetts have the advantage of samplingdiverse Aedes, as well as Cq. perturbans mos-quitoes. Information on the density and virus in-fection rate in these "bridge-vector" mosquitoesis useful in formulating an intervention decision,and this information will be lacking in a moni-toring program that does not include light traps.
Nestable fiber pots sample as many Cs. me-lanura, including virus-infected females, as doconventional resting boxes. Because diversekinds of mosquitoes, including anophelines, restin these pots, they may be useful for monitoringthe intensity of transmission of other mosquito-borne pathogens, such as human malaria.
We confirm that resting boxes fitted with fun-nel-like collapsible frames, which increase theapparent area of the entrance 9.6-fold, collectabout 6 times more mosquitoes than otherwisewould be collected (Edman et al, 1968). Oneperson, however, can service many more pots
FBsn Pors pon SnuplrNc Rrsrnqc MosQultor's 46'7Dncsl,aen 1995
than frame-mounted boxes in a given period of
time. and at far less cost. The disadvantages of
mounting frames, therefore, appear to outweighbenefits gained in collection efficacy.
Economic factors may influence the choice offiber pots over conventional resting boxes. Weestimate that a resting box can be procured forabout $15 and that a frame costs an additional$15. A fiber pot, in contrast, costs only $1.30(delivered). A 0.5-kg (1-lb) fiber pot weighs sig-nificantly less than a resting box (about 3 kg)and a plywood box with its frame (about 7 kg).The nestable feature of the fiber pots combinedwith their light weight promotes portability andstorage. Indeed, we believe that one person cancomfortably carry either 20 flber pots, 2 restingboxes, or one resting box with its accompanyingcollapsed frame. None of the 295 flber pots thatwe have installed appears to have lost structuralintegrity during 1 year of exposure to an accu-mulated IOO cm of precipitation. In Practice, wefound that mosquitoes can be harvested in halfthe time from a trapezoidal fiber pot than froma cuboidal resting box. Furthermore, we foundthat artiflcial illumination of the interior of theresting device was essential for mosquito collec-tion from plywood boxes, but not from fiberpots. Thus, monitoring programs that use fiberpots expend fewer resources than those usingconventional resting boxes.
Our experience with nestable fiber pots forsampling arbovirus vector mosquitoes encour-ages us to recommend their further evaluationfor use as sampling devices for mosquitoes thattransmit the agents of malaria, filariasis, RiftValley fever, and various other encephalitides.Use of these pots may facilitate routine moni-toring of vector mosquitoes.
ACKNOWLEDGMENTS
This research was supported in part by theMassachusetts Department of Public Health andthe Northeastern Mosquito Control Association.We thank Yvonne Chase of the Massachusetts
Department of Public Health for identification of
virus isolates.
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