502 J. A*. Mosg. Coxrnol Assoc. Vor. l, No.4

THE EFFICIENCYOF VARIOUS COLLECTION TECHNIQUES FOR SAMPLING CULEX ANNULIROSZRIS IN SOUTHEASTERN AUSTRALIA

RICHARD C. RUSSELL School of Public Health and Tropical Medicine, University of Sydney, New South Wales, 2006, Australia

ABSTRACT. Dry-ice (COr) baited EVS (Encephalitis Virus Surveillance) light traps collected significantly more Culex annulirostris than unbaited EVS or CDC light traps, chicken-, guinea pig- and rabbit-baited EVS traps, or cubic foot resting boxes. Results from the animal-baited traps indicated a preference for bird versus mammal bait. Females sampled by the resting boxes had significantly lower parity rates than females sampled by dry-ice baited EVS traps. Parity rates were generally similar among females sampled by dry-ice baited EVS traps, unbaited CDC light traps and animal baited EVS light traps.

INTRODUCTION trap) similar to the model of Goodwin (1942)1. Traps were set in pairs 20 m apart across the The mosquito Culex annulirostris Skuse is an prevailing breeze, and each test was replicated important vector of arboviruses from both bird three times. The traps were situated approx- and mammal reservoirs in Australia (Doherty imately 250 m from the major larval habitats at 1974). Mosquito populations can be monitored Appin, and approximately 2 km from the larval to predict seasons when above average abun- habitats at Echuca. dance can occur, and investigate the bionomics Female Cx. annulirosfris were counted and of the vector species that relate to its involve- parity status was determined according to the ment in virus cycles. The use of different tech- dissection technique of Detinova (1962). When niques may relate to the objectives of field in- collections were large, randomly collected sub- vestigations. This paper reports the results of a samples were dissected. Abundance data were study at two sites in southeastern Australia, in analysed by paired ,-test after square root which collecting techniques were compared to transformation, and the proportion of parous determine their relative efficiency for assessing females sampled were tested by Chi-square test. the relative abundance, host response and parity of female Cx. annulirostris. RESULTS AND DISCUSSION MATERIALS AND METHODS The dry-ice baited EVS trap collected the The first study area was in the Kanyapella greatest numbers of Cx. annulirosfrls, but was State Forest adjacent to the Kanyapella Basin almost ineffective if operated without dry-ice wildlife area, situated on the floodplain near (Table l). The CDC light trap collected signifi- the junction of the Goulburn and Murray riv- cantly fewer adults than the dry-ice baited EVS ers, 12 km east of Echuca in northcentral at both Appin and Echuca (p < 0.05). The EVS Victoria. Within the wildlife management area trap also collected more Cr. annuli,rostrk at both were artificial ponds maintained for waterfowl, locations when baited with dry-ice than when which were a major larval habitat for mos- baited with either a chicken or guinea pig. quitoes, particularly Cx. annulirostris. The sec- When the animal baits were compared, traps ond study area was in a dry sclerophyll forest baited with a chicken were superior to traps adjacent to Brian Road, Appin, New South baited with either a guinea pig (p < 0.01, p < Wales, approximately 70 km southwest of Syd- 0.05) or rabbit (p > 0.01, p < 0.05) at Appin ney. The area has been partially cleared for and Echuca, respectively. There was no signifi- grazing, and there are empoundments with cant difference in collection sizes when traps vegetated margins, which were larval habitas for were baited with either a guinea pig or rabbit. mosquitoes particularly Cx. annulirostris. Resting boxes were far more successful for During February 1980, field studies were ini- sampling female Cx. annulirostrls at Appin than tiated to compare collecting techniques includ- at Echuca, but they collected on average only ing a dry-ice (500 gm) baited EVS (Encephalitis 2-bVo as many as the dry-ice baited EVS trap. Virus Surveillance) light trap (Rohe and Fall Mafe Cx. annulirostris were regularly collected in 1979); an unbaited CDC light trap (Sudia and the resting boxes of the above traps. The CDC Chamberlain 1962); an unbaited EVS light trap occasionally collected males of the species, trap; EVS traps modified to accommodate small but the dry-ice and animal baited traps did not animals (chicken, guinea pig or rabbit-all ap- collect male Cx. annulirostrar on any occasion. proximately 500 gm); I cu ft resting boxes [5 Culex annulirostris responded more to traps boxes were used in each comparison per EVS baited with a chicken versus guinea pig at both DrcrMenn.1985 J. At"t. Mosq. CoNrnol Assoc. 503

Table l. Comparison of sampling techniques for determining the relative abundance and parity of Culex annulirostris at Appin, New South Wales and Echuca, Victoria, Australia February 1980.

Appin Echuca No. Prop. No. Prop. Sampling method Abundancer dissected parous Abundance dissected parous Dry-ice EVS t13.3*119.1) 200 0.58 972.9* (68.0) 200 0.88* Unbaited EVS s.3* (2.1) l6 0.69 6.0* (4.6) 18 0.55* Dry-ice EVS 99.3*123.9) 200 tr.5/ 1060.0* (92.b) 200 0.69 CDC light trap 39.3*(21.7) 100 0.63 627.7* (8s.b) 200 0.72 Dry-ice EVS ,63.7*119.5) 200 0.53* 706.3* (194.8) 200 0.70 Chicken EVS 46.7* (5.9) 100 0.65* 226.0* (21.9) 200 0.75 Dry-ice EVS 94.0*(15.1) 200 0.59 693.7* qr7z.7) 200 0.7| Guinea pig EVS 29.0* (8.2) 80 0.60 137.0* (27.5) 200 0.74 Chicken EVS 54.3*(14.6) 150 0.69 227.7* (59.4) 200 0.69 Guinea pig EVS 39.3,r,113.0) 90 0.62 t47.3* (41.6) 200 0.73 Chicken EVS 64.3 (r4.2) 150 0.60* 192.3* (17.6) 200 0.69 Rabbit EVS 47.7 (20.2) 100 0.47* 136.7* (24.0) 200 0.73 Guinea pig EVS b3.7 (6.7) 150 0.63 143.7 (44.4') 200 0.62{, Rabbit EVS 57.7 (4.2) 150 0.58 136.3 (17.5) 200 0.78r, Dry-ice EVS 127.3*(18.0) 200 0.70* 1627.7* (22t.6) 200 0.76* Rest-boxes (5) 31.0*(14.1) 90 0.43* 128.7* (26.2) 200 0.56*

I Mean number of mosquitoes per trap night (sample standard deviation). *: significantly different (at least at the p<0.05 level) as tested by paired t-test after square root transformation for the abundance values and by Chi-square test for the proportion parous values.

Echuca and Appin, and similarly responded to the present investigation. However the COz traps baited with a chicken versus rabbit at output from the dry-ice bait might have ex- Echuca. Comparisons of mammalian baits ceeded that from either animal, and may be showed that female Cx. annulirostris responded responsible for the greater number of mos- equally to traps baited with either a guinea pig quitoes collected by the dry-ice baited EVS trap or rabbit at Echuca or Appin. Thus in this study when compared to the animal baited traps. Cx. annulirostris responded more to birds than Culex annuliroslns females must be parous to to mammals as a possible bloodmeal source. be potentially infective for arboviruses, so es- In southern Australia Cx. annuliroslril has timating proportion parous in a population is been reported to feed on a wide variety of ani- epidemiologically important. The proportion mals (Dobrotworsky 1965, Lee et al. 1954, parous of a mosquito population can be used to Reeves et al. 1954). The baits used in this study estimate population survival rates and thus re- are not indigenous hosts, and may not necessar- lates to potential to survive to an infective age ily represent host feeding patterns of Cx. an- for transmitting arboviruses. Female Cx. an- nulirostris in southeastern Australia. The results nulirostris collected by dry-ice baited EVS traps from the present study indicate feeding pat- exhibited marginally lower parity rates than terns more associatedwith birds than mammals, females collected by the animal baited traps. and thus are at variance with the general con- Compared to a CDC light trap and guinea pig clusions of Kay et al. (1979) that Cx. annulirostris baited trap, the dry-ice baited EVS trap col- prefers mammal to bird hosts in Queensland lected a slightly smaller (not significant) pro- (with no evidence of a seasonal shift in host portion of parous females at both locations. preference), and Wright (1981) that rabbit However, when compared to chicken baited baited traps collected more Cx. annukrostris than traps, the dry-ice baited EVS trap collected a chicken or guinea pig baited traps in norrhern significantly (p < 0.01) lower proportion of Western Australia. The latter author suggested parous females only at Appin. At Appin fe- that the larger size of the rabbits, with their males collected at bird bait exhibited a higher relatively greater output of carbon dioxide, parous rate than females attracted to either could have been responsible for the advantage guinea pig (not significant) or rabbit bait (P < (along with the habit of the chickens of ingest- 0.05). At Echuca, however, the mammal baited ing captured mosquitoes). The use of similarly traps attracted a higher proportion of parous sized bait animals. and their isolation from the females than chicken baited raps. Parity among captured mosquitoes in the modified EVS trap females sampled by mammal baited traps var- was an attempt to overcome these problems in ied between locations. At Appin, there was no I I 504 J. Au. Mosg. CoNrrol Assoc. Vor. l, No.4

significant difference berween the proportions are alsodue to Assoc.Prof. G. Berry for statisti- parous attracted by guinea pig or rabbit bait, cal assistanceand Assoc.Prof. J. H. Bryan for but at Echuca the females attracted to the manuscript review. guinea pig bait had a significanrly (p < 0.05) lower parity rate than those attracted to the rabbit bait. The resting boxes sampled females with significantly lower parity rates than dry-ice ReferencesCited baited EVS traps at both Appin and Echuca (p < 0.05, p < 0.05 respecrively). Bidlingmayer, W. L. 1974. The influence of envi- ronmental factors and physiological stage on the Gillies (1974) discussed the problem of ob- flight patterns of mosquitoes taken in the vehicle taining a representative sample for determining aspirator and truck, suction, bait and New Jersey the physiological age of a mosquito population, light traps. J. Med. Entomol. ll:l19-146. and indicated that age composition of females Detinova, T. S. 1962. Age-grouping methods in Dip- in a sample may vary according to the method tera of medical importance with special reference and time of capture, geographical location and to some vectors of malaria. W.H.O. Monogr. Ser. physiological state of individual females. Si- 47:l-216. multaneous use of different sampling methods Dobrotworsky, N. V. 1965. The mosquitoes of Victoria. Melbourne which operate upon different principles has Univ. Press, Carlton. Doherty, R. L. 1974. Arthropod-borne viruses in been proposed by Bidlingmayer (1974) to ob- Australia and their relation to infection and dis- tain a more objective sampling of the popula- ease.Progr. Med. Virol. l7:13&-192. tion being investigated. It has been reported Feldlaufer, M. F. and W. J. Crans. 1979. The relative that CO2-baited traps collect a significantly attractiveness of carbon dioxide to parous and nul- greater proportion of nulliparous females than liparous mosquitoes.J. Med. Entomol. l5:140-142. light traps (Feldlaufer and Crans 1979, Mag- Gillies, M. T. 1974. Methods for assessingthe density narelli 1975), but a significantly higher propor- and survival ofblood-sucking Diptera. Annu. Rev. tion of parous females may be sampled by Entomol. L9:345-362. Gillies, M. T. CO2-baited traps than by artificial resring shel- 1980. The role of carbon dioxide in host finding by mosquitoes (Diptera: Culicidae): A re- ters (Milby et al. 1983). However, Morris and view. Bull. Entomol. Res. 70:525-532. DeFoliart (1969) reported variability in parity Goodwin, M. H-,Jr. 1942. Studies on artificial resting among different mosquito species sampled by places of Anophelzsquadrimaculatus. J. Natl. Malaria light and COr-baited traps. Parous rates were Soc. l:93-99. higher among female Culix tarsalis Coquillett Kay, B. H., P. F. L. Boreham and G. M. Williams. sampled by CO2-baited CDC light traps than 1979. Host preferences and feeding patterns of (Diptera: among females sampled by New Jersey light mosquitoes Culicidae) at Kowanyama, traps and resting boxes in California (Meyer et Cape York Peninsula, norrhern Queensland. Bull. Entomol. al. 1984). High parity rates have also been re- Res. 69:441-457. Lee, D. K.J. Clinton and A. K. O'Gower. 1954. ported for Culex salinarlzs Coquillett sampled by J., The blood sources of some Australian mosquitoes. CO2 trap (Slaff and Crans l98l). Epidemiologi- Aust. J. Biol. Sci. 7:282-3O1. cally, the host-seeking and parous component Magnarelli, L. A. 1975. Relative abundance and par- of a vector population is of most concern and ity o[ mosquitoes collected in dry-ice baited and individuals taken at CO2-baited traps are con- unbaited CDC miniature light traps. Mosq. News sidered to represenr rhe host-seeking popula- 35:350-353. tion (Gillies 1980, Reisen et al. 1983). Meyer, R. P., R. K. Washino, T. L. McKenzie and The dry-ice baited EVS trap can 6" ,"co*- C. K. Fukushima. 1984. Comparison of three methods for collecting mended as the superior collection method for adult mosquitoes associated with rice field and irrigated pasture habitats in female Cx. annulirostris in southeastern Austra- northern California. Mosq. News 44:315-320. lia, and this trap also representatively samples Milby, M. M., W. K. Reisen and W. C. Reeves. 1983. parous the component of the Cx. annulirostris Intercanyon movement of marked Culex tarsalis population at least as well as the other methods (Diptera: Culicidae).J. Med. Entomol. 20:193- 198. tested. Thus the dry-ice baited EVS trap would Morris, C. D. and G. R. DeFoliart. 1969. A comoari- be more suitable for collecting arbovirus pools son of mosquito catches with miniature light iraps than from CDC light traps or shelters. and COr-baited traps. Mosq. News 29424-426. Reeves, W. C., E. L. French, E. N. Marks and N. E. Kent. 1954. Murray Valley encephalitis: a survey of ACKNOWLEDGMENTS suspected mosquito vectors. Am. J. Trop. Med. Hyg. 3:147-159. The late Mr. J. Dawson, formerly Health Reisen, W. K., M. M. Milby, W. C. Reeves,R. P. Meyer Surveyor for the Echuca City Council, sug- and M. E. Bock. 1983. Population ecology of Culex gested the Kanyapella site for this study, and tarsalis (Diptera: Culicidae) in a foothill environ- accessto the Appin site was with permission of ment of Kern County, California: temporal the Macarthur Developmenr Board. Thanks changes in female relative abundance, reproductive Drcnnnrn, 1985 J. Ar"r.Mosq. CoN'rRoLAssoc. 505

status, and survivorship. Ann. Entomol. Soc. Am. Culex salinarius (Diptera: Culicidae) populations. J. 76:800-808. Med. Entomol. l8:6F-68. Rohe, D. L. and R. P. Fall. 1979. A miniature battery Sudia, W. D. and R. W. Chamberlain. 1962. Battery powered CO2 baited light trap for mosquito borne powered light trap, an improved model. Mosq. encephalitis surveillance. Bull. Soc. Vector Ecol. News 22:126-129. 4:21-27. Wright, A. E. 1981. Ord River arboviruses-mosquito Slaff, M. and W. J. Crans. 1981. The activity and captures during 1976/77. J. Aust. Entomol. Soc. physiological status of pre- and posthibernating 20:47-57.

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