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Tropical Biomedicine 22(2): 249251 (2005)

Research Note

A comparative study of adult mosquito trapping using dryice and yeast generated carbon dioxide

Oli, K.1, Jeffery, J.2 and Vythilingam, I.31 Vector Control Unit, P.O. Box 30, Suva Fiji Islands,2 Department of Parasitology and Medical Entomology, Faculty of Medicine, Universiti Kebangsaan Malaysia,50778 Kuala Lumpur, Malaysia3Parasitology Unit, Institute for Medical Research, Jalan Pahang 50588 Kuala Lumpur, Malaysia

Abstract. Adult mosquito collections were conducted for 12 weeks in two residential areasin Kuala Lumpur. The CDC light traps were compared using dry ice and yeast as sources ofcarbon dioxide attractants for mosquitoes. The efficacy of the dry ice baited trap wassignificant over yeast generated CO2 trap. The predominant species obtained were Culexquinquefasciatus, Stegomyia albopicta and Armigeres subalbatus.

Researchers have used CDC light traps tosample mosquito populations for manyyears (Service, 1976). However, it has beenfound that light traps on their own are notvery attractive to mosquitoes (Vythilingamet al., 1992). Most often the light traps areaugmented with carbon dioxide from dryice. However, in some remote areas whereit is difficult to obtain dry ice one ishampered in the collection of mosquitoesusing CDC light traps. In a recent studyin Japan Saitoh et al. (2004) evaluated theefficacy of yeast generated CO2 as anattractant for mosquitoes in fieldcollections by using yeast which convertssugar into CO2 and ethyl alcohol.

Thus the objective of this study was tocompare the efficacy of CDC light trapsusing CO2 from two different sources.

Two sites were selected in KualaLumpur and mosquito trapping wasconducted from June to August 2005.Federal Hill is an upper middle classresidential area situated in the heart ofKuala Lumpur. It is surrounded by forest.The second site was 3 km away from the

Institute of Medical Research whichhouses the staff quarters.

Four traps were operated in each areafrom 1800 hours each night to 0600 hoursthe following morning. In each area twoCDC light traps were augmented withdry ice (Vythilingam et al., 1992) whileanother two used CO2 generated fromyeast mixture. A five liter plastic bottlecontained the mixture of 18 gm yeast(Saccharomyces cerevisaie), 250 gm ofsugar and 3250 ml of water. The five Lbottle was connected to a 500 ml bottlewith tubes. The smaller volume bottle wasused to hold the overflow water solution.CO2 generated was released from a 5mmhole on the side of the 500 ml bottle. Arubber tube was connected from the bottleand placed near the CDC light trapentrance. The yeast mixture was preparedfive hours prior to setting up the traps. Thefour traps were arranged in a quadrate andthe position of the two sources of CO2 wasrotated for each collection. Distancebetween the traps varied between 1.7 m to5m on different collection days.

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Although other insects were present,only mosquitoes collected during thestudy were counted and identified tospecies. Number of mosquitoes/trap/nightwere transformed to log (X+1). Thistransformation is necessary in view of themany influences other than populationchanges that affect the size of trapcollections (Bidlingmayer, 1969). Thetransformed data were statisticallyanalysed using the SPSS program for t testand mean comparison.

A total of 864 mosquitoes werecollected of which 677 (mean log 0.9748)was from the dry ice augmented trap and187 (mean log 0.4696) from the yeastgenerated CO2 trap. Therefore the efficacyof dry ice as an attractant for mosquitoeswas significant (P=0.00). The predominantspecies was Culex quinquefasciatus,followed by Stegomyia albopicta andArmigeres subalbatus (Table 1). Therewas a significant difference for all threespecies between the two traps indicatingthat the trap augmented with dry ice wasmore efficient than the yeast generatedCO2 trap.

Similar results were obtained bySaitoh et al. (2004) in their experiment.The amount of CO2 released is important

in attracting the mosquitoes. Thus oneway would be to increase the yeastsugar mixture so that more CO2 will beobtained. Petric et al. (1995) studied therelationship between sample size andevening temperatures in order to providebetter standardized CO2 baited trapsamples. They reported that blood seekingactivity of mosquitoes showed a significantcorrelation with evening temperature.However, the catch ratio depended moreon the CO2 baited traps. In addition,research by Vythilingam et al. (1992) inMalaysia, using CO2 and octenolaugmented CDC light traps gave increasedyields of trapped mosquitoes.

It has been well established thatCDC trap without CO2 is not attractive tomosquitoes. CDC traps augmented withCO2 from dry ice is an efficient trap.However, since it is difficult to obtain dryice in many remote areas in tropicalcountries, yeast generated CO2 traps couldbe used since it is easily available andcheap. Thus this technique should befurther researched and evaluated to makeits use feasible in regions where obtainingdry ice is an obstacle to conductingeffective mosquito surveillance.

Table 1. The calculated means for the different mosquito species collected andthe P values at the 95% confidence interval

Species Trap N Mean log t- value P value

Culex quinquefasciatus Dry ice 36 0.7222Yeast 36 0.3328 3.101 0.003

Culex vishnui Dry ice 36 0.0551Yeast 36 0.0084 1.808 0.075

Stegomyia albopicta Dry ice 36 0.4318Yeast 36 0.2048 2.576 0.012

Stegomyia aegypti Dry ice 36 0.1330Yeast 36 0.0000 1 0.321

Armigeres subalbatus Dry ice 36 0.2422Yeast 36 0.0216 3.620 0.001

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Acknowledgements. The authors wish tothank Dr. Ng Kok Han, Director Institutefor Medical Research for his permission topublish this paper, staff of EntomologyUnit, IMR especially Mr. Rosman S for helpin setting up the traps. The 1st author wassupported by WHO to conduct this projectas part of fulfillment for Diploma inApplied Parasitology and Entomology.

REFERENCES

Bidlingmayer, W.L. (1969). The use oflogarithms in analyzing trap collections.Mosquito News 29: 635-640.

Petric, D., Zgomba, M., Ludwig, M. &Becker, N. (1995). Dependence ofCO2 baited suction trap captures ontemperature variations. Journal ofAmerican Mosquito ControlAssociation 11: 6-10.

Saitoh, Y., Hattori, J., Chinone, S., Nihei, N.,Tsuda, Y., Kurahashi, H. & Kobayashi,M. (2004). Yeast generated CO2 as aconvenient source of carbon dioxidefor adult mosquito sampling. Journalof American Mosquito ControlAssociation 20: 261-264.

Service, M.W. (1976). Mosquito ecology.Field sampling methods. AppliedScience Publications, London, 583 pp.

Vythilingam, I., Chiang, G.L. & Chan, S.T.(1992). Evaluation of carbon dioxideand 1-Octen-3-ol as mosquitoattractants. Southeast Asian JournalTropical Medicine Public Health 23:328-331.