Journal of the Ameican Mosquito Contol Association, 12(3):491-493, 1996Copyright O 1996 by the American Mosquito Control Association, Inc.

CONSTRUCTION OF A FIELD TRAP FOR INITIATING ANOVIPOSITIONAL RESPONSE IN AEDES TAENIORHYNCHUS

E LANCE WALLACE

Departmcnt of Biology, l7l Moultrie Street,The Citadel, Charleston, SC 29409

ABSTRACT An oviposition trap w:rs constructed for the black saltmarsh mosquito, Aedes taenio-rhynchus. The trap consisted of a 50 x 60-cm piece of contaminated 1007o cotton bath towel, saturatedwith 85Vo tap water, a container, and a cover of dried plant parts placed over the contaminated toweling.This combination initiated oviposition. Contamination of the toweling was due to populations of bacteriaand fungi. The eggs recovered were free from soil and debris.

Bentley and Day (1989) stated: "A tremen-dous amount has been written concerning mos-quito oviposition. A large proportion ofthe stud-ies have dealt with laboratory investigations onmosquito response to chemical and physical as-pects of the oviposition site; relatively few fieldstudies have been attempted." The field studiesconducted have largely employed either the re-moval of eggs from the soil with the use of somemechanical device (Horsfall 1956, Service 1968,Miura 1972, Trpis 197a) or placing the soil fromoviposition sites in water and counting the num-ber of larvae that hatch (Bradley and Travis1942, Bidlingmayer and Schoof 1956, Elmoreand Fay 1958). Service (1976) emphasized thategg sampling is more difficult and time consum-ing than larval surveys because of the problemsencountered in extracting the eggs from the soiland debris.

In addition to numerous studies on laboratoryinvestigations of chemicals as oviposition attrac-tants, some studies have focused on the impor-tance of bacteria as oviposition attractants. Ger-hardt (1959) suggested that adult female mos-quitoes were attracted to test plots by com-pounds resulting from the anaerobic decay oforganic materials. Rockett (1987) demonstratedthe ovipositional response of Culex pipiensLinn. to bacterial attractants. Hazard et. al.(1967) commented that gravid floodwater mos-quitoes were no doubt attracted to odors pro-duced by fermentation. In the laboratory theydemonstrated the olfactory attraction of Aedesaegypti (Linn.) and Culex quinquefascinras Sayto chemicals produced by bacteria.

The purpose of this research was to developan oviposition field trap for the black saltmarshmosquito, Aedes taeniorhynchus (Wiedemann).The attractant consists of a IOOVo cotton towelcontaminated with a microorganism populationcomposed largely of bacteria and fungi. Otherfactors that proved to be important for initiatingoviposition were a container, a high moisture

percentage, and plant materials for covering thetowels.

The study was conducted near the coast atFolly Beach, SC from July I I to August 9,1995.The site chosen was a high marsh inlet, open totidal flushing. Water remains in the inlet basinfor long periods of time due to poor drainageand an accumulation of rainwater. This circum-stance has led to the accumulation of a layer oforganic matter in the basin. The dominant veg-etation along the embankment and in the basinis Spartina alterniflora, Loisel, Salicomia vir-ginica Lrnn., Iva frutescens Linn., Myrica ceri-fera Linn., and Fimbristylis spadicea (Linn.).

The rap (Fig. l) is simple in its construction.The design consists of an upper and lowerMacCourt black plastic tub (purchased at Lo-we's Home Centers) measuring 20 X 60 X 90cm. The upper tub is supported at each cornerby a I.27 X 120-cm steel rebar rod. The rodsare pushed into the ground approximately 8O cmallowing for a clearance of about 20 cm betweenthe top and bottom tubs. The bottom tub con-tains the contaminated towel covered by plantmaterials.

A randomized block of 8 traps was arrangedin 2 rows of 4 traps each in a 3 X 4-cm plot,near a sloping embankment of the inlet. Fourtraps were used as treatment traps and 4 as con-trols. Bath towels of lOOTo cotton containing ap-proximately 6OVo tap water were contaminatedby spores of airborne microorganisms over a pe-riod of 2-3 wk in the laboratory. Four pieces ofcontaminated toweling, which measured 50 X6O cm, were saturated with tap water andweighed. Water was removed by squeezing untilthe difference in the amount of water at satura-tion and the amount removed was approximately857o moisture. Four uncontaminated pieces ofthe same size and percentage of moisture servedas controls. A piece of contaminated or uncon-taminated toweling was placed, at random, ineach tub. Each piece was covered by plant partssuch as dried pine needles and bark, or leaves

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Other factors were tested, such a sulfides, l7osalt solution, and a slurry of ground plant parts,but those found to be significant in initiating ovi-position were a combination of a container, acover, approximately 857o moisture, and a con-taminated l(X)7o cotton towel.

The choice of the container was based on sizeand not color. It was felt that the larger the con-tainer the better would be the chance of recov-ering eggs. Later it was discovered that ovipo-sition would take place in smaller containers.Eggs were recovered from red, white, and darkgreen containers and from different colored tow-els. Tests were conducted over a 24-h period.The heaviest oviposition occurred from dusk todawn. A smaller number of eggs were recoveredduring the daytime. This information, coupledwith the fact that the toweling was covered withplant materials, indicates that color does not playa significant role in initiating oviposition.

The selection of the type of cover was basedon the observation of the material found at theoviposition site. It was felt that the natural odorof plant material would not interfere with theodor coming from the contaminated towels. Oth-er materials may also work, but those selectedwere easy to acqufue and proved to be effective.

Knight and Baker (1962), in a laboratorystudy on the role of substrate moisture, foundthat the optimum percentage was 65Vo. The in-formation from that study was used in selectingthe amount of moisture believed to be significantin initiating oviposition. It was observed in thefield that very few eggs were recovered fromsaturated or dried toweling. The largest numbersof eggs were recovered from towels with 857omoisture content. In weighing the towels after a24-h period, moisture decreased approximately25Vo. This was the reason for choosing the 85Volevel ratler than the 65Vo level reported byKnight and Baker (1962).

This research was jointly funded by The Cit-adel Development Foundation and The Interna-tional Center for Public Health Research. Ap-preciation is extended to Dwight C. Williams.The International Center for Public Health Re-search; Martin G. Hyatt, Charleston Mosquito

Abatement Program; Robert E. Zack, George-town County Mosquito Control Program; MacA. Tidwell, University of South Carolina; B. JoeKelley, The Citadel, for assisting with the statis-tics; and Alix Darden, The Citadel, for review-ing the paper. I would like to thank the manyCitadel cadets who assisted over the years anda very special thanks to my wife Julia A. Wal-lace for putting up with the marsh mud and longhours of absence.

REFERENCES CITEDBentley, M. D. and J. F, Day. 1989. Chemical ecology

and behavioral aspects of mosquito oviposition.Annu. Rev. Entomol. 34:4Ol-421.

Bidlingmayer, W. L. and H. F, Schoof. 1956. Studieson the viability of salt-marsh mosquito eggs. Mosq.News 16:298-301.

Bradley, G. H. and B. V- Travis. 1942. Soil samplingfor studying distribution of mosquito eggs on saltmarshes in Florida. Proc. N.J. Mosq. Exterm. Assoc.29:143-146.

Elmore, C. M. and R. W. Fay. 1958. Aedes sollicitansand, A. taeniorhynchus larval emergence from sodsamples. Mosq. News 18:23O-233.

Gerhardt, R. 1959. The influence of soil fermentationon oviposition site selection by mosquitoes. Mosq.News 19:151-155.

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Miura, T, 1972. Laboratory and field evaluation of asonic sifter as a mosquito egg extractor. Mosq. News32:433-436.

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Service, M. W. 1968. A method of extracting mos-quito eggs from soil samples taken from ovipositionsites. Ann. Trop. Med. Parasitol. 62:478-48O.

Service, M. W. 1976. Mosquito ecology. John Wiley& Sons. New York.

Trpis, M. 1974. An improved appruatus for separationof mosquito eggs from soil. Zentralbl. Bakteriol.Hyg. 226:418-423.