JUNE 1987 Moseutro PnrnocpNs AND PARASITES 23r
FIELD INCIDENCE OF MOSQUITO PATHOGENS AND PARASITES IN CENTRAL ALBERTA
MARK S, GOET'TELI
Department of Entomolngt, (Jniuersity of Aherta, Edrnonton, Aherta, T6G 2E3
ABSTRACT. Ten pools and ponds were monitored on a weekry basis _for pr-esence-9f mosquito Microsporidia '""ap"ifrog"* "na parasites over a tlree year period near Edmonton, Alberta-.-Acari, fungi, p""tit.i.ftida were found associatei witlh mosquitoes. Percentage of collections with pathogens and in parentheses 'iestimated'%o".urii". tpt"ralence) followed by the mean percintage infection within the samples, incidence) for the three year period were as follows: Coelnmom-yces-psorophnrae uar. psoroDhnrac0.9(0.01-0.02), Culicirnmycis claiisporus 1.2(0.09-0.2),Saprolegniales 50-1(15), Smittium- !r. zf.otnf . Uiciosporidia'i0.9(0.6-1.4), Peritricliida 43.4(30)and Acari 3.2(0.04).The high incidgnce of S'"otoiumi"i.. -"y b. a resuli of attack on stressed individuals under laboratory conditions.. S-e-v.9r$ ["It ""& ."""try records are reported. It is concludedthat pathogensand parasites generally had little effect on the mosquito populations'
visu- INTRODUCTION pae) were brought back to the laboratory, ally examined for presenceof pathogels or -par- Recently there has been much interest in use asites, counted and placed into Bates' medium of pathogensand parasites as control agents of S (Mclintock 1952) in trays or 500 ml plastic mosquitoes.Many potential control agentshave containers.Immatures were rearedat 20'C until been identified (see Jenkins 1964, Roberts and emergenceor death. Dead larvae were removed Castillo 1980,Roberts and Strand 1977,Roberts daily, identified to speciesusing the key of Wood et al. 1983), however, most of these represent et ai. (19?9),and then examinedmicroscopically limited collectionsand very little is known about for sigrrsof pathogens and parasites. At times, their epizootiology.Very few studies have been dead immatures were stored at 4'C for 24-48hr parasite made to determine fluctuations in ac- prior- to examination. tivity or the long term incidence of parasites. PathngenI parosite identificatinns/ isol'ations' Such studies are required in order to better Pupae parasitized by mites were removed and evaluate pathogens and parasites as potential plaied in a separatecontainer until adult emer- biological control agents of mosquitoes' The gence.Adults were then examined for mite in- present study was made to determine impor- festation. Mites preserved in 70Voalcohol were tance and seasonalincidence of naturally occur- sent to Dr I. M. Smith, BiosystematicsResearch ring mosquito pathogens and parasites in 10 Centre, Ottawa for identification. selectedpools in central Alberta. Microsporidian-infected immatures were kept at 4'C in sterile water and sent to Dr A. H. Animals MATERIALS AND METHODS Undeen, Insects Affecting Man and ResearchLaboratory, Gainesville, FL, for iden- Larual rnonitoring an'd'd.iagnasis. Ten pools tification. Whole cadavers with Coelnmotnyces and ponds 4 km NW of Devon, Alberta infections were mounted on slides in lactofuch- (114"47'W, 53'23'N) were regularly monitored sin and identified using the key of Couch and between June 1982 and September 1984. In Bland (1985). Immatures infected with fungi 1982, monitoring began June 15; in 1983 on other than Coelomom.yceswere bathed for 5 min April 28; and in 1984 on May 6. Five to 120 in 50 pg/ml chloromycetin before being placed (usually 10-30) samples were taken from each on the surface of Sabouraud dextrose agar sup- pool on a weekly basis using a 350 ml dipper. plemented with 60 pg/ml penicillin and 30 pS/ During each field trip, pool parameters such as ml streptomycin. Hyphal growth on the agar water temperature (taken 10 cm below the water was subcultured until pure cultures were ob- surface),pH and conductivity were monitored. tained. Saprolegrriaceousfungi were subcultured Dippers and the collectors' boots were rinsed in onto 2.5% V8@juice with 2% agar and sent for 5% householdbleach aft'ercollection at eachsite identification to Dr D. J. S. Barr, Biosystematics in order to minimize the possibility of spreading ResearchCentre, Ottawa. -pathogens between study sites. Initial attempts were made to isolate pure Field-collectedimmatures (i.e., larvae and pu- cultures of most fungal pathogens.However, due to the high incidence of fungi in the order Sap- and difficulties associatedin isola- 1Present address:Insect Pathology ResourceCen- rolegniales this was discontinued ter, Boyce Thompson Institute, Tower Road, Cornell tion and identification, only University, Ithaca, NY 14853. after the first few months. Subsequently JounNer,oF THEAnrnnrclx Moseurro CoNrnol AssocrATroN Vol.3, No.2
Culicirwmyces clguisporus Couch, Romney and All other sites were monitored for the entire Rao was isolated;details are presentedelsewhere study period as long as they contained water. (Goettel et al. 1984). No attempts were made to Properties of the water were generally similar at isolate trichomycete fungi. These were preserved all sites. Temperatures of bitween B and 5.C in lactofuchsin on slides and were sent for iden- were recordedin early spring. The highest tem- tification to Dr R. W. Lichtwardt, Department perature recordedwas 2b"C at sites H and I. At of Botany, The University of Kansas, iawrence. the other sites, the highest temperaturesranged "be- Peritrichida were not identified. No attempts between 20 and 24"C. Conduciivity ranged were made to identifu or isolate possible bacle- tw-een105 and 1710pmhos/cm and pH bitween rial pathogens. 6.0 and 9.2. In 1982 and 1983,the total rainfall Percent inri.d,ence estimates.Since large num- betwee.nJune and August was approximately B0 bers of mosquitoes were unaccounted f6r while cm while in 1984 during the sameperiod it was reared under laboratory conditions and only 5.5 cm (Environment Canada,Edmonton Inter- dead immatures were examined for pathogens national Airport 14 km SE of the study area). and parasites,three methods *ere .rred to 6sti- As a result, in 1984most pools were dry by late mate infection rates of field-collected mosqui- summer. toes as follows: Mosquitoes.In general, pools were first colo- nized- Minimum estimated Voincidence by spring Aedes species.Specimens col_ (1) lected included: Aedes cataphy[ta Dyar, Ae. : numbbr infected/total collected x 100. eu Table 1. Descriptions of pools in central Alberta monitored for mosquito pathogensand parasitesbetween June 1982and September1984. Sit€ Habitat description Vegetationr Size (m) A Shallow, semipermanentpool in Carex.sp. (d) 15x34 partially wooded area Populus spp, Salir sp. (e) Typln latifoli.a (s) Shallow, temporary roadsideditch Calthasp.(s) 1x8 ScJr.rsp. (s) Typlw latifolia (s) Deep, semipermanent roadside pool Iamrn rninnr 25x50 with seepagefrom adjacent lake Solir sp. (s) Typha latifolia (s) D Same as C Sameas C 3UX40 E Shallow, temporary roadsideditch Carer sp. (d) 2x25 Typlwlatifolia (s) F Large shallow marsh fed by stream Caltlwsp. 210x 210 Corer sp. (d) P opul.us balsamif er a (s) Salrr sp. Twlnlatifolia (g) Large shallow marsh Carer sp, (d) 600x 750 Sclir sp. (s) TWlwlatitolia (s) H Permanent pond Carer sp. (d) 25x50 Lemrnmircr (d) Solir sp. (s) Shallow, temporary roadside pool Ccrer sp. (d) 18x25 Solir sp. (s) Typlw latifolia (s) Sameas I Sameas I 30x50 I d : dominant,s = scattered chida had the highest incidence (Table 2). The On June 28,44larvae (3 first, 35 second,6third- Ieast abundant organisms were Acari, Coelomo- instar) were collected in 10 dips and on July 12, rnyce s and Culicinomy ce s. 33 larvae (8 first, 11 second, 14 third) and 50 Incidences of pathogens and parasites were pupae were collectcd in 5 dips. The single-in- generally too low to make any comparisonsbe- ?ectedlarva from the June 28 collection died 17 tween pools and years. There were no apparent days post-collection while the 2lawae from the correlations b€tweenpool parametersand infec- .luiv iz collection died 6 and 9 days post-collec- tion rates. Details of pool parameters are there- tion. fore presented only f.or C. clauisporusas very Coelnrnomycespsoroph.orae var, psorophorae little is known about its occurrencein nature. has been collected from many mosquito hosts and habitats world-wide (Couch and Bland 1985). In Canada C. psoroplwrae vat. psoroph' FUNGI orae is widely distributed and well established Coelamomyces.Only 4 larvae were found in- in southern Alberta occurring in larvae of Cs. fected with Coelnmomyceson 3 occasionsand at inornnta and less commonly in Ae. uerons (She- 2 sites. All were identified as Coelornomycespso- manchuk 1959,Zebold et al. 1979).Incidences roplwrae var,psorophorae Couch with Ae. uexans ofup to 80% have been observedin Cs' irwrnata as the only host. The first infection was detected (Shemanchuk 1977) while in 1956, 12% of alL at site J on July 23, t982. This pool was flooded Cs. inornata were infected (Shemanchuk 1959). as a result of heavy rain in the first week of July Coelomomryceshas also been reported from Ae. and was colonizedby large numbers of Ae. uex- triuittatus (Coq.) in Manitoba (Taylor et al. ons. The sample consisted of 11 dips which 1980).These authors reported incidencerates of yielded 581 larvae (primarily fourth-instar) and up to 56% in field-collected mosquitges, l-row; 43 pupae. The infected larva died 3 days post- ever, infections were apparent in blood-fed collection. adults only. Infection rates in the present study The second and third occurrenceswere de- may therefore have been higher since adults tected on June 28 and July 12, 1983 at site A. were not examined.In the Manitoba study how- 234 Jounnnr,oF THEAupuceN Moseurro CoNrnoLAssocrerrot Vor,.3. No. 2 qtr Ee l I r I rA \tr |l rt 9r OrO|l Orrll Nll c\ Ol t'- Oi 6t 6 '= 5Q in ilq :f (O OJOJ ^{ O) ^d) o ^t-o) roct (o@ o@ . tocoo €: r@ rr i(0 | <0 (l)(9i @rr or@ l@@ r@ lr@m .: di *9 Xx -q xx o Ai im @cO F- O)C6O @ii rO Od O@ r c6 c,o 6'= (o\o ts-co i d (o(o {r $r Fl ^- $9 @r F-O)$ () EX >H h o k\ H= stE q oQ: c6a O t' xe o lO -'= { I Cl ^lO cY.dl.\': q a6. I tNt ol , I O^ lO) 6rt ttsl H I dd I irq I | | lN I im cad lo h 'rl.a HI o cl) S; 6l o) c! r@ oca o q >a Ni i @N i .iE--tt 8c o i,E cl , 6tS Nt-a rO - c')^ i.: o gA iN I iN6l cO I c\ l< dm The first occurrenceof mites was on June 24 aL of field-collected immatures to laboratory con' site E at which time a single spring Aedes sp. ditions probably stresses the individuals as evi- pupa was collected with 156 mites attached. denced by the high mortality rates witnessed. These immatures were identified as belonging Stressed individuals may become targets for "pathogens" to the genusA rrenunsby Dr I. M. Smith. Mites such as Soprolegnia. Most inci- encountered subsequently were not identified. dencesof Saprolegnialeswere probably the re- The prevalencefor 1982 was IlTo with an esti- sult of such attacks; experiments with controls mated incidencerate of 0.5Vo(expressed as num- are required before the potential of these fungi ber of pupae infected/total number of pupae as control agents is ruled out. (2) Since imma- collected). tures were held in the laboratory, infections may Mosquito-parasitizing mites have a wide geo- have been acquired in the laboratory. As dis- graphical distribution and Arrenurus spp. are cussedabove, this probably occurred with Sap- the most common (Mullen 1975).It is generally rolegniales since many cadavers were observed believedthat mites reducefecundity and longev- while the fungus was releasingzoospores. Some ity of their host and therefore have biological C. clavisporu.sinfections were also probably lab' controlpotential (Smith 1983).Larvae of Amen- oratory-acquired as larvae died of infection up uru.s spp. are common in the tropics and sub- to 23 days post-collection. (3) Large numbers of tropics and in some populations the prevalence immatures disappearedbetween the time of col- of parasitization can rcach ffiVo. In temperate lection and the time the last individual either regions mosquitoes are generally parasitized died or emerged as an adult. only occasionally,but prevalencewithin a pop- In order to estimate incidence in the field as ulation may be high (see references in Smith accuratelyas possibletaking the aboveproblems 1983). into consideration, 3 methods were used. Meth- In the present study, mites were found infect- ods 1 and 2 werc used for Coelomam'yces,Culi- ing spring Aedesspecies, Cs. inornata, Cs. min- cinornycesand Microsporidia to give an esti- ncsotoeand Cr tetitans; Cs. minnesotoe is a mated range of percent incidence. It is assumed new host record. Previously mites were found that the possibility of laboratory acquired infec- on spring Aedes species and Cs. innrrwta in tions is minimal (in the case of Coelamomyces Alberta and onCx. territans in Quebec(Leprince and Culicirwmryces,the numbers found were so 1981,Mullen 1975). low that laboratory acquired infections would Pathogens rwt found.. It is interesting that have little effect on the estimates in any case). neither viruses nor nematodes were found. Method 3 was used for Smittiurn sp. and Peri- There are no records of viruses from mosquito trichida as only dead larvae were diagnosed. larvae in Canada, however they are probably Since these organisms are generally considered "host", distributed worldwide (Federici 1985). Inci- not detrimental to their it can be as' dencesof virus diseasein nature are usually less sumedthat the sameproportion of all immatures than LVo,but epizootics with infection rates of collected were infected as those that died and up to 70% occur (Federici 1985). It is highly were accountedfor. If on the other hand, these unlikely that in the present study infections of organisms contributed to the death of the mos' iridoviruses were overlooked.This diseaseis one quitoes, this is an inaccurate method for esti- of the easiest to diagnose as infected larvae are mating field incidence. iridescent. Several suspectspecimens were sent Concluding remnrhs. Even though difficulties to Dr B. A. Federici, University of California, were encounteredin accurately estimating inci- Riverside and were confirmed as being virus- dence in the fiel4 pathogens and parasites ap- free. pear to have had little effect on the larval mos- There are numerous records of nematodes quito populations studied. Similar observations from mosquitoesin Canada (Roberts et al. 1983, were made by Service (1977) in England. In a 6- Roberts and Strand 1977, Roberts and Castillo year study of Ae. cantoins, he estimated that 1980) and most infections are also easily diag- although 95% Iawal and pupal mortality oc- nosed. It can be concluded that viruses and curred, few were killed by pathogensand para- pathogens were either totally absent from the sites. 10 sites during the study period or occurred at The many new locality and host records re- such a low Ievel that they were not detected. ported in the present study further demonstrate Effects on lwEt population. It is diffrcult to that the known geographical distributions of assessthe field incidence ofpathogens and par- pathogens and parasites are only a reflection of asites and their impact on the mosquito popu- the geographicdistribution of entomologistsin- Iation especially when they occur at very low terested in pathogens and parasites of mosqui- levels. Specific difficulties encountered in the toes (Chapman 1974).The extremely low prev- present study include the following: (1) Transfer alence and incidence of some pathogens dem- 238 Jounxll oF THEAunnrcln Moseurro Conrnol Assocrlrrol Vor,.3. No. 2 onstrates how difficult it is to establish such ectoparasites de moustiques (Diptera: Culicidae) du recordsunless long term studiesare undertaken. lac Boivin, Granby, Quebec.Can. J. Zool. 59:&-18. In terms of control of mosquitoes, the wide Lichtwardt, R. W. 1976.Trichomycetes. pp. 651-671. geographicaldistribution and Iow incidence of .In: E. B. Gareth Jones (ed). Recent advances in aquatic mycology. pathogensand parasitesin nature indicates that Elek Science,London. Mclintock, J. 1952.Continuous laboratory rearing the inoculative method of biological of control may Culiseta inorrnto (Wilt.) (Diptera: Culicidae).Mosq. not be successful.Therefore inundative use of News 12:195-201. these pathogens and parasites will probably be Mullen, G. A. 1975.Acarine parasites of mosquitoes. required. Further, if parasitesand pathogensare I. A critical review of all known recordsof mosqui- ever to be fully exploited for mosquito control, toes parasitized by mites. J. Med. Entomol. 12: a much better understanding of biotic and 27-36. abiotic conditions causing epizootics is neces- Rioux, J. A. and F. Achard. 1956. Entomophytose sary. mortelle a Saprolcgnia declinc Humphrey 1892 dans un elevage d' Aedes berlnndi Seguy 1921. Vie et Milieu 7:32G-337. ACKNOWLEDGMENTS Roberts, D. W. and J. M. Castiilo (eds). 1980. Bibli- ography on pathogens of medically impodant ar. I would like to thank S. Aaltonen, K. Fry, T. thropods: 1980.Bull. W. H. O. 58 (Suppl. 1). Lam and C. Seadonfor technical assistance:D. Roberts,D. W., R. A. Daoust and S. P. Wraight. 1983. C. Currie for help in habitat descriptions;J. Bibliography on pathogens of medically important Roland for useful discussions;D. M. Wood for arthropods:1981. W. H. O. VBC/83.1. advice and help in mosquito identifications; B. Roberts, D. W. and M. A. Strand (eds). 19?7.Patho- gens of medically A. Federici for advice on virus diagnosis; important anthropods. BuIL W. D. J. H. O. 55 (Suppl.1). S. Barr, R. W. Lichtwardt, L. Sigler,I. M. Smith Service,M. W. 1977.Ecological and biological studies and A. H. Undeen for pathogen and parasite on Aedes cantans (Meig.) (Diptera: Culicidae) in identifications; and H. C. Chapman, J. Harlos southern England. J. Appl. Ecol. 14:159-196. and R. Currah for critically reading the manu- Shemanchuk,J. A. 1959.Note on Coelornornycespso- script. This work was supported by funds from roplnrae Couch, a fungu.s parasitic on mosquito the Pesticide ChemicalsBranch, Pollution Con- larvae. Can. Entomol. 9l:743-744. trol Division, Alberta Environment to D. A. Shemanchuk, J. A. 1977. Biological control of mos- Craig. quitoes.Canada Agl.ic.22(4):25-26. Smith, B. P. 1983.The potential of mites as biological control agentsof mosquitoes.pp. 79-85.In: M. Hoy, REFENENCESCITED G. Cunningham and L. Knutson (eds). Research needsfor developmentof biological control of pests Andreadis,T. G. 1983.An epizooticArnblyospora sp. by mites. Agric. Exp. Stn. Univ. Calif. Spec. PubI. (Microspora:Amblyosporidae) in field populations No. 3304. ofthe mosquitoAedes cantator. J. Invertebr.Pathol. Sweeney,A. W. 1981.An undescribedspecies of Smit- 42:427-430. tium (Trichomycetes) pathogenic to mosquito lar- Chapman,H. C. 1974.Biological control of mosquito vae in Australia. Trans. Br. Mycol. Soc. 77:55*60. larvae.Annu, Rev. Entomol. 19:33-59. Taylor, B. W., J. A. Harlos and R. A. Brust. 1980. Couch,J. N. and C. E. Bland. 1985.Taxonomy. pp. Coelomomycesinfection of the adult female mos- 8l-297./n; J. N. Couchand C. E. Bland (eds).The quito Aedes triuittatus (Coquillett) in Manitoba. GenusCoebmornyces. Academic Press, New York. Can.J. Zool.58:1215-1219. Couch,J. N., S. V. Romneyand B. Rao.19?4. A new Welch, H. E. 1960.Effects of protozoan parasitesand funguswhich attacksmosquitoes and relatedDip- corrmensals on larvae of the mosquito Aedes com- tera.Mycologia 66:374-379. munis (DeGeer) (Diptera: Culicidae) at Churchill, Federici,B. A. 1985.Viral pathogens.pp. 62-74.In: Manitoba. J. Invertebr. Pathol. 2:389-395. H. C. Chapman(ed). Biological control of mosqui- Williams, M. C. and R. W. Lichtwardt. 1972.Infection toes.Am. Mosq.Control Assoc. Bull. 6. of Aedes aegypti lawae by axenic cultures of the Goettel,M. S., L. Siglerand J. W. 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Inventaire prEliminaire tion in the mosquito pathogen Coelnmarnycespso- d'acariens (Acari:Hydrophantidae et Arrenuridae) roplwrae. Can. J. Bot. 57:27ffi-2770.