JOURNAL oF THE AMERTCAN Mosquno corqrnol Assochrrolr vol,. 4. No. 4

SUBURBAN ACCUMULATIONS OF DISCARDED TIRES INNORTHEASTERN ILLINOIS AND

THEIR ASSOCIATED MOSQUITOES

DONALD L. BAUMGARTNER

Northwest Mosquito Abatement District, 142 W. Hintz Road, Wh,eeling, IL 60090

A-BSTRACT.-In response to a growing, human suburban population and an escalating problem ofused tire disposal, a summer-long survey of discarded tires and their associated mosquitoes wij conductedin northeastern Illinois in 1985. Within a 291 km2 area, a monthly average of ?,823lires were distributedamong 127 sources classified into 7 categories: fields/ditches (25% of total sources); salvage yards (?%);trucking/construction companies (13%); woodlots (15%); school playgrounds 1fi%); s&vice staiions(l6Vo); and tire dealers (11%). Distribution and abundance of each souice category appeared to reflectIocal land-usage and extent of urbanization. Wooded sites surpassed service stations, dealers, and salvageyards in the average percentage of flooded tires (86% vs. 25Vo ea.) and percentage of those lawal-infested(58% vs. 25Vo ea.). Overall,6,398 mosquito larvae emong g species were collected witlr,Cubx restuans(82%) and' Cx. pipicns (13%) predominating. Species segregations with respect to the tire source arerevealed. Possible control strategies ofmosquitoes in tires are summarized.

INTRODUCTION

Discarded tires have long been recogrrized asa larval habitat for some mosquitoes but todayare emerging as important contributing sourcesof particular species in urban areas, especiallythose which normally reproduce in tree holesfAedes triseriattrc (Say)], containers lAedes ae-gypti (Linn.), Aedes ahopictus (Skuse)], androck holes lAedes atropalpus (Coq.)1. Recently,the problem of tire accumulation, disposal, andmosquito breeding therein has escalated in re-sponse to an ever-growing human population,increasing sale and use of automobiles, and con-comitant reduction of natural breeding sites inurban areas. In the United States. the sale ofmerchandise by tire dealers has increased 7l%from 1977 to 1982 (Anonymous 1984), with anincreasing number of unscrupulous tire dealers,trucking companies, and disposal companiesdumping waste tires in fields and woodlots forconvenience, rather than paying high disposalfees. An estimated 200 million tires are dis-carded annually in the U.S. (see Beier et al.1983a) with few options available for their ulti-mate disposal. Additionally, the importation ofwaste tires from abroad has contributed to theproblem (Reiter and Sprenger 1987). Cul.ex pi-picns Linn., Ae. acgypti, and Ae. triseriatus arcamong the more important disease-vectoringmosquitoes in the U.S.A. which frequently breedin tires, in close proximity to human dwellingsand activity (Beier et al. 1983b).

The tire problem is magnified by growingevidence that tires promote rapid developmentof mosquitoes and enhance their vector ability.Pupation of. Ae. triseriatus occurs nearly amonth earlier in discarded tires than in treeholes, with a greater percentage of females pro-duced in the former (Haramis 1984). Female Ae.triseriatus derived from tires may be more ag-

gressive and efficient in feeding, and depositmore eggs per cluster than tree hole derivedcolonies (Means et al. 1977). Aedes atropalptnemerging from rock pools are entirely autoge-nous during their first gonotrophic cycle whilethose from tires readily take blood (Restifo andLanzaro 1980). Tire habitats tend to yieldsmaller, perhaps nutritionally deprived Ae. tri-seriatus females which may transmit La Crosse(LAC) encephalitis virus at elevated rates (Har-amis 1984, Paulson and Kobayashi 1985).

Although tire-breeding mosquitoes have beenwell studied in Indiana (Beier et al. 1983a,1983b; Berry and Craig 1984), Iittle is known oftire mosquito dynamics in other states. Servicestations, tire dealers, and salvage yards are com-mon sources of discarded tires but knowledge oftheir incidence and relative importance in mos-quito production is lacking. In this investigationan attempt was made to locate the majority ofsources and accumulations of discarded tires inan Illinois suburban area and determine theirmosquito production. The effect of tire storagepatterns on water retention and mosquito colo-nization, and habitat partitioning with respectto tire size and seasonalitv were also investi-gated.

METHODS

From mid-April to late November, 1985, anintensive effort was made to locate and map allaccumulations of discarded rubber tires withina 29I km2 suburban area (population 404,800,1980 census) in northwestern Cook County,northeastern Illinois. Few extensive tracts offorest or farmland remain, with the southernthird ofthe study region heavily industrialized.

Any accumulation of 2 or more tires, withoutmounted rims, in woods or fields was considered

502 JounNu, oF THE AnrpnlclN Mosqulro CoNrRor, AssocrerroN V o L . 4 , N o . 4

number containing water and number of thesewith mosquito larvael and, sporadically, tirewater temperature and pH. Tires mounted onrims do not hold water generally and so wereexcluded. Ten to 20 tires/size-class/site wereinspected for the presence of mosquito larvae.At least 3 to 5 randomly chosen tires at eachsite were sampled for surface larvae with a short-handled dipper (300 ml), the number of instarsrecorded, and the samples pooled per size class/site/day. No tire was sampled more than onceand all sampled tires were from surface piles.Tire water was not mixed prior to sampling,acknowledging that collection data densitiesmay be misleading due to larval aggregation ordisturbance (larvae diving to bottom). All sam-ples were secured with a minimum of disturb-ance or shading of tires. Larvae collected fromtires were transported to the laboratory andrefrigerated at 4'C for 1-4 days for convenienceprior to identification. All identifications arebased on third or fourth instars, using Ross andHorsfall (1965) and Siverly (1972). Voucherspecimens were deposited at the U.S. NationalMuseum. Adult mosquito recoveries from 6 NewJersey light traps, roughly spaced 7 km equidis-tant throughout the survey area and operatingnightly all summer, were compared with larvalrecoveries from tires for seasonal differences.

AII mosquito-infested tires were treated withB. t. i. (B ac illus thuringiensis v ar. is r ael.ensls Ber-Iiner) on corncob granules (5-10/tire, 0.8%active ingredient, Sandoz Inc.) following inspec-tion. The physical attributes of this carrier madeit well suited for easy dispersion and deep pen-etration to lowermost tires in piles. This inspec-tion and monitoring was repeated 5 timesthroughout the summer (May-August) atroughly monthly intervals for 51 sites. Manyother sites were subsequently discovered duringan intensive fall/winter survey and remappingof regrrlar mosquito sources at a time whenIeaves had fallen from deciduous trees andground vegetation was sparse. These latter siteswere sampled only once up to November 14,after which time the temperature dropped,freez-ing all standing water. The entire survey wasconducted during a relatively dry season;monthly mean temperatures and precipitationwere 1.1"C and 12.6 mm, respectively, lowerthan normal (20.1'C and 91.4 mm, respectively,N.O.A.A. at O'Hare Airport). It is doubtful thatthe mosquito control efforts enacted within theDistrict during this study greatly affected mos-quito breeding in tires; adulticiding was mini-mally practiced and the majority of larvicidingactivities were directed against floodwater Aedesuexans (Meigen), which is rarely reported fromtires (Beier et al. 1983a).

In order to determine if partitioning exists

among mosquito species in tires of differentsizes, all tires were grouped into 1 of 3 sizeclasses, and the data and larvae collected notedwith respect to these classes. Automobile tireswere the smallest, generally measuring ca. 0.7 mdiam and containing 8-11 liters of water in avertical position, 4-6 liters laying on its sidehorizontally, and ca. 5 liters in a partiallystacked, diagonal position. Truck tires were in-termediate in size (ca. 1 m diam), usually con-taining 14 liters of water when standing verti-cally. Tractor tires were the largest (ca. 1.8 rhdiam), retaining ca. 76 liters of water in a hori-zontal position and ca. 62 liters when partiallystacked. A few even larger (2 m diam) tires fromearth movers were encountered, which held 190liters of water in a horizontal position.

RESULTS

Tire sources. Within the 291 km2 suburbanarea of northeastern Illinois, 127 sources ofdis-carded tires were located, containing a meantotal standing crop of 7,823 tires per month(Table 1). Prior to this intensive survey, only 7sources were known, mapped, and regularly in-spected. Field/ditch sites comprised 25% of the127 sources, with the remainder equally dividedamong service stations (16%), wooded lots( 1 5 % ), trucking/construction companies ( 13 % ),school playgrounds (ll%), and, tire dealers(11%). Auto salvage yards with tires were scan-tily represented(7%). However, all salvage yards(n : 9) within the study area possessed tireswhich mosquitoes could colonize, while only17% ofschool playgrounds (n :86), 38Vo oftftedealers (n = 37), 41% ofwoodlots (n = 46), and42% of service stations (n : 50) inspected hadsuch tire deposits.

The category and number of tire sources be-tween different townships appeared to reflectthe overall land usage and extent of urbaniza-tion. Fewer total sources were found in the 2most urbanized townships (n : 56,166 km2 area,pop. 260,520) than the more suburban ones (n:71,L25 km2 area, pop. 144,280). Tires in fields/ditches and woodlots made up a large part ofsources (68%, n: 34) in the least urbanizedarca (61% urban land cover) where tires werecommonly disposed of in 1 to 5 acre woodlotsintermingled among populated areas and farm-Iand rather than in forest preserve tracts whichare regularly policed and maintained by stateemployees. Trucking/construction companysources were prevalent in the more heavily in-dustrialized township; the number of sites there(n : 10) are probably underreported since it wasnot possible or feasible to inspect behind everycompany building. Service station and tiredealer sources were prevalent (43% of sites, n :

DECEMBER 1988 SusunsA.N TIRE MoSQUIToES

Table 1. Mean number of tires per month deposited at various sites over entire season which breedmosquitoes.

Tire size class Mean tiresper

site + SESource Truck TractorNo.

sitesrTotal( % )

Fields/ditchesService stationsWoodlotsTruck/constr.School playgrd.Tire dealerAuto salvageTotal(%)

I Sites are excluded which possessed abnormally large numbers oftires (5-10x norm), atypical ofthe majorityof sites. This includes a service station (i : 312 car), woodlot (190 car), three truck/construction companies(1?8 truck, 210 and 478 car), two tire dealers (450 truck, 182 tractor), and a salvage yard (971 car).

2 Total increases to 7.823 tires when large site accumulations mentioned above are included.

a t

2018t4I O

t28

tt7

2271,009

r23tt2285

r,541638

3,935(81)

373 (8)1,009 (21)

r42 (3)603 (12)447 (9)

1,5e6 (33)682 (14)

4,8522

1 2 ! 45 0 + 88 + 3

4 3 + 53 4 + 7

133 + 258 5 r 3 9

r42 40 0

1 9 0457 34t62 0o o u4 4 0

879 38(18) (1 )

56) in the most populated and urbanized town-ships. School playgrounds (3-5/township) andauto salvage yards (2-3/township) containingwaste tires were evenly distributed among alltownships. A preliminary suwey of an affluentrural area of equal land coverage, adjacent toand west of the study area, indicates that farfewer tires (among ca. 25 sources) are discardedin fields/ditches and woods there. with the ab-sence of many of the service stations, tire deal-ers, and construction companies common to themore populated, lower income, eastern half ofthe District. However, on rural farmlands sev-eral small, old tire accumulations were discov-ered in farm waste heaps behind barns and atmargins of corn fields.

The total number of unmounted outdoor tireswithin the District is presented in Table 1. Au-tomobile tires dominated most sources except attrucking/construction companies, which fre-quently discarded Iarger truck and tractor tires.Accumulations of tires at service stations. tiredealers, and salvage yards accounted for 66% ofthe tires (n : 7,823) available for mosquitocolonization. with the mean number of tires ata single site/source also high (50, 133, 85, re-spectively). Fewer mean tires per site were dis-carded in fields/ditches (12) and woodlots (8).

Other sources of waste tires were encounteredwhich were not surveyed for water content ormosquito larvae and not included in this study,but nevertheless deserve mention. Twelve au-tomobile tires were found scattered on the lawnand bare gtound at a seldom used police academytraining facility. Sixty truck and 130 automobiletires were discovered in a refuse pile near theservice hanger of a small, Iocal airport. Auto-mobile tires (n = 139) scattered among weedymargins of a gravel parking lot served as abumper guard at a retail business. Tires dis-carded by construction firms were observed near

land development areas. Numerous tires wereused to delineate a race track at a go-cart estab-Iishment. Tires lacking drainage holes have alsobeen sighted in park playgrounds behind severalday-care (nursery) centers. Tires were presentoutdoors, behind some privrite residences (2-13/yard), contributing to the overall mosquito prob-lem. In older neighborhoods with large yardsand mature trees (5-10 residences/mile2) water-filled tires (l-2 / yafi) suspended from tree limbswere common in backyards for children's recre-ation, albeit infrequently used and continuallycollecting rainwater and leaf litter to supportmosquito populations. Outside the survey regiontires were also used as holddowns for large tar-paulins at a garden nursery; as guides for adriveway and as bumper guards at factorydocks.

Method of storage and their frequency of re-moval are critical factors which determine waterand organic matter accumulation in tires, andinfluence mosquito colonization. Tires at fields,woods, and salvage yard sites were considered tobe permanent with little rernoval or disturbancethroughout the entire study. Such was not thecase at service stations and tire dealers where,upon questioning, 18 managers profess to havetheir discarded tires removed by a disposal ser-vice at mean intervals of 13 + 7 days (range 7-30). Extremes omitted from this average are 2service stations which disposed of tires at 2 dayand 6 month intervals. All tires in fields/ditchesand woodlots, and most at salvage yards andconstruction companies were randomly scat-tered about which maximized their water collec-tion, while tires at service stations and tire deal-ers were frequently vertically stacked or shinglestacked horizontally (Fig. 1). A survey of auto-mobile tires stored at service stations and tiredealers over the summer confirmed the suspi-cion that vertically stacked tires are less likely

JounNer, oF THE AunRrcnN Moseurro CohlrRol AssocrerroN V o L . 4 , N o . 4

to trap rain water than scattered tires. withthose shingle stacked intermediate. Signifi-cantly fewer (x2 : 40, P < 0.01) verticallystacked tires held water (227o, n : 1,382) at thetime of inspection compared to scattered tires(32Vo, n: 1,980), with shingle stacked tiresintermediate (28%, n : 4,497). However, 2EVo(n : 298) of these water-filled column stackedtires contained larvae compared to 4l% (n :1,254) of shingle stacked and only I4To (n :626) of scattered, flooded tires (all significantlydifferent, x2 : t47, df:2, P < 0.01)-

The mean number of water-filled tires andmosquito breeding in all automobile tires fromeach of the 7 sources were compared. Servicestations, dealers, salvage yards, and construc-tion companies exhibited similar mean percent-ages of tires containing water (ca, 257o) and,mean proportion of these breeding (ca. 25%)over the entire season. Wooded sites differedthough, with 86% of tires water-filled and 58Voof these mosquito infested. Too few field/ditchand playground sites were surveyed for anymeaningful conclusion. Generally, mosquito lar-vae were rare in tires situated in direct sun, ongravel or cement, and/or away from vegetation,while those in the shade, under trees, and/or ongrass beds bred abundantly.

Species segregation. During this study 413samples (73% from service stations, tire dealers,and trucking/construction companies) contain-ing 6,398 mosquito larvae among 9 species werecollected from tires (Table 2\. Culex restuansTheobald and C x. pipiens comprised 82 and. L3Vo,respectively, of the larvae collected. Cul.ex terri-fons Walker, Culex salinarjus Coq., and. Ae. tri-seriatus were rarer, each representing l-2% ofthe total collections. Anopheles punctipennis(Say), Aedes hendersoni Cockerell, Orthopodo-myia signifera (Coq.) and Culex tarsalis Coq.were scarce, all totaling less than 1%. Otherimmature flies (Chironomidae, Stratiomyidae,Psychodidae, and Syrphidae) were also occa-

sionally recovered from woodlot tires. Larvae ofCx. restuans, Cx. pipiens, Ae. triserintus, Ae.hendersoni, and Or. signiferawerc abundant andactive in the cool water of sun-exposed tires upto the first freeze on November 14 (middav airtemp. 4-7"C, water 5-7'C)

Data in Table 2 shows that species are gen-erally indiscriminate and do not preferentiallyoviposit in tires of different size classes. Addi-tionally, the mean number of larvae/dip (300ml) in auto (20.3 + 24.2), truck (15.5 + 12.2),and tractor tires (11.1 + 8.5) declined slightlywith increasing tire size, suggesting that ovipo-sitions do not greatly increase with increasingwater volume or surface area. Tractor tires hold13-fold more water volume than auto tires butlarval density was one-half as much.

Species exhibited segregation with respect tothe tire source (Table 3). Culex restuans wasmost frequently encountered at service stationsand represented the majority of species breedingat all other sources. Culexpipiens was second ofimportance at all sources, showing minimalbreeding at service stations and school play-grounds. Culex territans and Cr. salinarius wererare at service stations and tire dealers, with theformer collected mostly from trucking compa-nies and salvage yards, and the latter fromtrucking companies, fields/ditches, and wood-lots. Aedes triseriatus, Ae. hendersoni, and Or.signifera were found only in wooded sources.Overall, tires in woodlots supported the greatestspecies diversity and service stations the least.

Aedes triseriatus infested auto and truck tiresin woodlots, varying in size from 10 to 1,560 m2,with 7-85 m (mode 25 m) the shortest distancefrom these tires to nearby human habitation.From August to October, only 6-ll% of thervater-filled tires available for mosquito coloni-zation in woodlots (n : 133) contained Ae. tri-seriatus, the remainder infested with either Cr.restuans or Cx. pipiens. Frequently, Ae. triseri-ot&s was the dominant or sole species when

Table 2. Number (percent/tire size) of mosquito larvae sampled from tires (May-November, 1985).

Tire size class Total

SpeciesAuto(269)1

Truck(e5)

Tractor(4e) %

Cx. restuansCx. pipiensCx. tenitansCx. salinariusAe. triseriatusOr. signiferaAn. punctipennisAe. hendersoniCx. tarsalisTotal

3,774 (84)536 (12)45 (1)37 (1 )70 (2)18/q

1

4,494

e57 (80)135 (1r)46 (4)3e (3)6

l1 ,190

543 (76)1.42 (20)12 (2)12 (2)00

00

7t4

5,274813103887620l 1I 12

6,398

8213211

<l<1<1<<1100

I Number of dipper samples (300 ml ea).

DECEMBER 1988 SusunseN TIRB MosQuttoes

Table 3. Frequency (%) of species per source/frequency source per specres.

Source of used tires

505

Species

Service Tire Truckstation dealer co.(109)1 (78) (116)

FieldSchool2 ditch Woods

(5) (34) (55)

Autosalvage

(16)Total(413)

Cx. restuansCx. pipiensCx. territansCx. salinariusAe. trberiatusOr. signiferaAn. punctipennisAe. hendersoniCx. tarsalisTotal

30/8e L7/7622/10 26/189/<r 3013

rc/<r 30121/<r

27/<r 45/<1

50/<r1,800 r,t67 375 78

4/57 5/50 5,274L3/3r 18/25 813r4l4 9/2 1033018 2614 88

9S/r3 76100/4 2027 /<1 11

100/2 1150/<r 2338 566 6,398

381e6e/49/<r

2,074

6/851812524/75/r

9/926/8

1 Number of dipper samples, 300 ml ea.'Source sampled meagerly and only in early fall.

present in tires, with associated Culex speciesrare or absent, while nearby (1-2 m) organicallyrich tires lackingAe. triseriatus often held largenumbers of Cul.ex.

Species seasonality. Proportions of Cx. res-tuans ftomtires remained hieh (98% of allCul.exspp.) and stable through May and June, decreas-ing slightly in July (90%, n: 1,401) and sub-stantially so in August (65%,n: 1,393). Lighttrap collections of this species followed a similar,but more substantial, seasonal decline; repre-senting 37% of all Culex spp. (n = 386) in Mayto 5% (n: 928) in August. Culex pipiens, notpresent in tires until July (9.6%), peaked inAugust (29%), while light trap collections reflectits presence throughout the summer (62% May-June) with increases in the latter half (95% inJdy, 88% in August). Culex tenitans was equallyrepresented throughout the season in tires andtraps; C. salinarius only appeared in late sum-mer.

DISCUSSION

The results indicate that a potentially large,unrealized number of tires may be hidden in thesuburbs of large metropolitan areas, contribut-ing significantly to the seasonal populationgrowth of particular, medically important mos-quitoes. Although most of these accumulationsmay be relatively small, they should not beoverlooked but regularly monitored as addi-tional mosquito breeding sites since their cu-mulative number can be quite substantial.Sources of these tires are numerous, but mostcan be grouped into 1 of 7 categories with theabundance ofthese different sources a reflectionof local land usage and development. For ex-ample, in St. Joseph Co., Indiana, salvage yardsand tire dealers were productive sources of mos-quitoes, with larvae recovered from 60-100% of

exposed tires (Beier et al. 1983b), but in thisstudy larval infestations at these sources weremuch lower e5%\. Differences in the surround-ing urbanization, tire turnover time, organiccontent, and weather are just some of thesefactors which may account for this discrepancy.The apparent paucity of tire sources in the moreaffluent, rural western half of the District andgreater abundance in more urban, lower incomeeastern half agrees with another survey in Lou-isiana which found that the economic level ofthe resident human population definitely influ-ences the number of artificial containers depos-ited (Chambers et al. 1986).

Although every effort was made to locate andsample all waste tires within the survey area,several hundred additional scrap tires discardedin backyards were excluded since it was impos-sible to inspect every residence. Backyard tireaccumulations may be important contributingsources of urban, disease-vectoring mosquitoes(Hedberg et al. 1985, M. A. Parsons, personalcommunication). Other surveys of smaller resi-dential areas have yielded backyard tire frequen-cies of3/block to l/household, representing 25-31% of all larval positive backyard containers(Chambers et al. 1986). Once again, the averageeconomic income of the surveyed area influencesthese proportions.

Tire orientation influences water accumula-tion and subsequent mosquito colonization. Asignificantly greater proportion of scattered tiresat service stations and dealers contained water(32%) as compared to vertically stacked tires(22%), but the percentage of these larval-in-fested was inversely related (14 vs 25%, respec-tively). The greater sun exposure of scatteredtires likely deters Culex oviposition as observedin sunny, subsurface concrete containers(Baumgartner 1987).

All of the 9 mosquito species recovered from

JouRNu, oF THE Aurnrcen Moseurro Cor.trRor, AssocrarroN V o L . 4 , N o . 4

tires in northeastern Illinois (Table 2) have alscrbeen reported from tires elsewhere (Rupp 1977,Barton 1978, Gordon and Peterson 1980, hestifoand Lanzaro 1980; Beier et al. 1988a, lgg3b).However, the relative proportion ofeach ofthesespecies differs from 2 tire surveys in nearbyIndiana (Beier et al. 1988a, 1988b); likely areflection of environments and habitats uniqueto this study. Culex restuans and Cr. pipi.enscomprised 82 and 13%, respectively, of a[ Ervaecollected from mostly sun.exposed tires while inIndiana each represented, l8-52Vo and.6-8To,respectively, of mosquitoes from exposed tires.Proportions of Cx. tenitans, Or. si6nifera, andAn. punctipennis werc in agreement with Indi-ana populations while Ae. triseriatus was rarelvencountered in northern Illinois (1%) but wasmore abundant (15-23%) in Indiana. Amongshaded tires in Indiana, Ae. triseriattrc was pre-dominant (62-89%), and Cr. restuans (74b,%\and Cr. pipiens (0.2-4Vo) were lesser constitu-ents. In this study, shaded tires of woodlotscontained a much lower percentage of Ae. tri-seriatus (13%) with Cx. restuans (.50%l and Cx.pipiens (25Vo) mote prevalent (Table B). Therelatively dry season during this survey couldaccount for the lower proportion of Ae. triseri-afus since frequent rainfall and floodwater arenecessary to stimulate the hatching of eggs.However, the species proportions herein re-ported are in better agreement with data col-lected by Berry and Craig (1984) from recentlydiscarded tires at the same tire yards in Indiana,showing that Cr. restu.ans, Cx. pipiens, and. Ae.triseriatus comprised 92Vo, l7o, and, !Vo, respec-tively, of the exposed tires and g0%, <I%, and8%. respectively, of shaded tires. As the waterin tires age, they are reported to undergo asuccession of species from Cr. restuans to Ae.triseriatus (Blaustein 1983). The closer fit ofspecies proportions from Illinois suburban tiresto that of "colonizing" tires (Berry and Craig1984) than to "aged" tires (Beier et al. 1983a,1983b) reaffirms the fact that most tires encoun-tered in this study were of recent depositions.Aedes aegypti, Ae. atropalpus, Ae. albopictus, Ae.uexans, Toxorhynchites rutilus septentrionalisDyar and Kn ab, Anopheles barberi Coq., Culisetamelanura (Coq.), and Orthopodomyia alba Baketare among the other species known to occur, ormay range, in Illinois (Ross and Horsfall 196b)and have inhabited tires elsewhere (ref. cit.) butwere not collected in this study. However, theformer 3 species have been subsequently re-covered from a large tire dump in Chicago (40km distant from study site), likely introductionswithin tires imported from southern states (BobFarmer, Clarke Outdoor Spraying Co., personalcommunication, Sept. 1987). The great produc-tivity of Cr. restuans and.Cx. pipicns from north-

e-rn Illinois tires, in close proximity to humandwellings, and their implicated role as an avianamplifier and bird-to-man vector, respectively,of St. Louis encephalitis (see Baumgartner 19gi)poses a constant threat to residents.

Each category oftire source provides a differ-ent habitat which, in turn, dictates a particulararray of mosquito species (Tables 2 and B).Species such as Cx. restuans, Cx. pipiens, Cx.territahs, Cx. salinarius, and An. punctipenniswhich are able to tolerate a wide range ol habi-tats (Siverly 1972) were present in varying butsimilar proportions intraspecifically at iachsource. The low species diversity and predomi-nance of Cx. restuans at service stations (9G%oftotal spp.) is likely a reflection of rapid turn-over (i : 13 days) and minimal leaf debrisaccumulation in these tires since it is a pioneerspecies of new tire habitats (Berry and Craig1984). Aedes triseri.atus, Or. signifera, and. Ae.hendersoni, which normally inhabit tree holesin forests, were mostly recovered from smallerauto tires of woodlots and rare or absent in thelarger truck and tractor tires on open ground atall other sources. This preference of Ae. triser-iatus for shaded tires rich in organic materialhas been repeatedly observed in Indiana (Beieret al. 1983a, 1983b; Berry and Craig 1984).

The preponderance of Ae. triserintus in wood-lot tires (Table 3) is not particularly surprisingsince it is principally a forest, tree hole species(Siverly 1972). All the necessary requirementsof a prime oviposition site such as shade, roughtextured and dark-colored walls, presence of or-ganic matter, and dark-colored water (Wilton1968) are met in woodland tires. Aedes triseria-tus readily attacks humans and is the primaryvector of LAC encephalitis in the upper midwest(Clark et al. 1983). OId tires containing Ae.triseriatus near residences in Minnesota (Hed-berg et al. 1985) and Ohio (Gordon and Peterson1980) have been incriminated as the majorsource of LAC cases. The close proximity (7-85m) of Ae. triserintus infested tires to humanactivity as found in this study implies that res-idents near woodlots containing tires are at anelevated risk for LAC encephalitis since it isknoWn to disperse 100 m from woodlands intoopen terrain in search of blood meals and ovi-position sites (Mather and DeFoliart 1984).Aedes triseriofus is also emerging as an impor-tant vector of canine heartworm [Dirofilariaimmitis (Leidy)l in the Midwest (Rogers andNewson 1979).

Seasonality of the predominant mosquito spe-cies recovered from tires generally agrees withtheir phenolory in Indiana tires (Berry andCraig 1984), and from light traps and othercontainer collections within the survey area(Baumgartner 1987). The large representation

SusuRslN Trnr MosQulrons 507DECEMBER 1988

of larval Cx. restuans over C.r. pipiens in tires(65 vs 5% of all Culex larvae, respectively' inAugust) despite an abundance of adult Cx. pi-piens in the environment (29 vs. 88%, respec-tively, from light traps) suggests that tires areselectively favored and generally more attractiveto Cx. restualr.s than Cx. pipiens. Species com-positions from other tire surveys support this(Beier et al. 1983a, 1983b; Berry and Craig1984). AlthoughCx. restuans is generally consid-ered a cool weather, spring species (Siverly1972), its abundance throughout the summer intires in Connecticut (Andreadis 1988) andherein reported, and summer abundance in con-struction sites (Baumgartner 1987), suggest thatit may be more prevalent during warm periodsthan previously thought or implied by Iight trapcollections.

Control of tire mosquitoes in metropolitansuburbs may involve several possible strategies,depending on the source category. Informationalpamphlets may be distributed to service sta-tions, tire dealers, and salvage yards alertingthem to the hazard. Indoor storage or outdoorstorage of tires under a roof would certainlyprevent rainwater entry and associated mos-quito colonization. If outdoor roofs are not pos-sible or desired, mosquito production can beminimized by combining frequent disposal withcareful storage; vertical stacking of tires in steeppyramids, rather than shingle stacking or ran-dom scattering, so that only uppermost tiresreceive rainwater, and in sunny areas away fromvegetation. Those businesses concerned withdisposal should not discard tires in landfillsbecause of eventual resurfacing but may accepttires for: recapping; shredding for use in moldedproducts, playgrounds, or asphalt (Frank 1981);or incineration to produce electricity or oil(Anonymous 1987). Tires deposited at schoolplaygrounds should: possess large (>5 cm)drainage holes to prevent water accumulation;be placed on sand beds, not woodchips or lawns,and; be regularly inspected for clogged drainholes. Wood chips, frequently employed as asubstrate for playgrounds, are not recommendedaround tires because they are easily kicked intotires and are excellent mosquito ovipositiona^attractants and larval growth propagators wheninundated (see Baumgartner 1987). Discardedtires in woodlots, fields, and ditches may beregularly monitored and treated with granularinsecticides or removed and properly disposed.For many mosquito abatement districts tire re-moval, perhaps best performed during fall andwinter months, is less expensive than periodiccontrol and is the best permanent solution (S.A. Wagner, Saginaw Valley Mosquito Abate-ment, MI, personal communication). In the caseof backyard, residential tire sources, the public

can be directed to disposal facilities or instructedto retain only rim-mounted tires outdoors'Abatement district cooperation with local andstate governments in developing legislation andenforcing a tire removal and storage ordinanceis certainly advantageous. Besides these, severalother options exist for the utilization of dis-carded tires (Reiter and Sprenger 1987). As apossible future control technique, predaceoustree hole mosquitoes (Toxorhynchitfes spp.) arecurrently being evaluated as biocontrol agentsfor container-breeding mosquitoes (Focks et al.1985).

ACKNOWLEDGMENTS

Numerous owners and managers of servicestations, tire dealers, trucking/constructioncompanies, and salvage yards graciously permit-ted me access to their property and cooperatedwith the study. Dr. R. S. Nasci (McNeese StateUniversity, Lake Charles, LA), Dr. G. R. De-Foliart (University of Wisconsin, Madison), Dr.L. D. Haramis (Illinois Department of PublicHealth, Springfield), and Ms. M. A. Parsons(Vector-borne Disease Unit, Ohio Departmentof Health, Columbus) reviewed the manuscriptand offered suggestions for its improvement.Two anonymous reviewers provided critical re-views helpful to the final synthesis. This studywas financed by the Northwest Mosquito Abate-ment District.

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