MencH. 1986 J. Ar"r.Mosq. Corrnol Assoc. ll

AUTOGENYIN C(ILEXANNULIROSTR/S FROM AUSTRALIA

ABsrrAcr.rn the raboralo.i. f#;',i; ?r"#tiliJ:J;y:T:i#':^rrom BrisbaneandM'dura, Austialia respectively were autogenous when reared and maintained on nutrient rich diets. Females reared and/or maintained on poor dieti mainly had ovaries at Christophers' stage I and exhibited from 0 to O.1Vo autogeny. All autogenous females had previously mated. Insemination rates in the and Mildura coloiies respectivel!, were 72.8Vo and 78.-8%. No.autogeny was detected in 997 females reared from 7 localities throughouiQueensland but this may have been due totheir poorer nutritional status (as indicated b-yyi-ng size) o. -o*.. likeli to a low insemination rate of 0 to 16/o. Our laboratory results, particularly with well-fed females, may have litile relevance to the field situation, where adults are generally smaller and less well-nourished.

INTRODUCTION into 420 x 310 mm rearing trays containing 500 ml tap water. One group was reared on a Culex annuliroslris Skuse is considered the high diet, 7.5 mg/larva, using ground Harper's "Dog major vector of arboviruses such as Murray Chow" and yeast in a 3: I ratio for all days virus Vailey encephalitis, Kunjin and Ross River except the first when 100 mg powdered yeast in Australia (Doherty 1974). On biological and was provided. Pupae were harvested and placed morphological characteristics, this speciescould in two 0.7 m3 cages, one with 25% sucrose and be considered a counterpart of Cx. tarsalis the other with 5%. The second group of larvae (Coquillett) in North America and Cx. were reared on a poor diet of 2'5 mg/larva and tritaeniorhynchls Giles in Asia (Reeves et al. adults maintained on 5% sucrose. 1954). As with Cx. tritaeniorhynchus, Cx. an- In order to estimate differences in the rate of nulirostris has been recognized as being autogeny between sibling groups, egg rafts anautogenous, in contrast to Cx' larsalls which werJreared individually on high diet and the produies eggs both autogenously and adults maintained on 25Vo suctose. After l2- 14 -79oC anautdgenously (Kardos 1959, Spadoni et al. davs. all of these females were stored at r974). for ovary dissection. The number of first instar During 1982, while dissecting Cr. a.nnulirostris larvae from any rafts produced were counted' reared on different diets, JDE noted that l9 of Late instar larvae and pupae were collectec 111 females reared on a rich diet (8.4 mg/larva) from nutrient-rich effluent ponds at 7 localities well developed ova either at stage IV or V had in Queensland (Dalby, Tara, Mitchell, Roma' (Christophers lgll). As these adults had been Charleville. and Kowanyama) and held in a 0.7 m3 cage on 25% sucrose solution the adults maintained for 7-15 days with 2570 (a) for 12-14 days, this suggested autogenous sucrose solution. Some nulliparous females egg development or (b) unobserved blood were also collected from Kowanyama using a feeding on an attendant during the process of battery-powered aspirator (Kay 1983). The This food replenishment and cage cleaning. ovaries and sperrnathecae of the females were (a)' paper reports findings relating to option examined. Fernales were judged to be autogenous if sugar fed individuals contained I (or more) MATERIALS AND METHODS mature (Christophers' stage IVb or V) ovum after the 12-14 day holding period. Nutritional of vector bionomics, 2 To facilitate studies status was detennined by measuring wing were established; colonies of Cx. annulirostris length from the axilliary incision to wing tip. one from , (McDonald et al. 1977), which was later supplernented several times with specimens from Mildura, and one from Brisbane (Mottram et al' in press). Sper- RESULTS females from both colonies were mathecae of Wing length of fernales reared on high and the insemination rate. examined to establish low diet respectively, ranged frorn 3.6 to 3.8 newly hatched Cx. annulirostris Batches of 250 rnrn and 3.1 to 3.3 mm. Of those Cx. annulirostris random frorn colony oviposition were taken at fed high diets as larvae and 25% sucrose as 50- 100 egg rafts and pipetted trays containing adults, 163 of 1,915 (8.5%) and 66 of l'292 (5.1%) of the Brisbane and Mildura colonies respectively, were autogenous (Table l). For the I Institute of Medical Research, Queensland Brisbane colony, expression was significantly Bramston Terrace, Herston, Blisbane, Australia with both high larval and adult 4006. greater-in those (8.5%) to those fed a high 2 Department of Entomology, University of Massa- nutrition compared (1" P<0.01)' chusetts.Arnherst. MA 01003. larval but poor adult dier (0'7%) L2 J. Ar"r.Mosq. CoNrnol Assoc. Vor.2, No. I

f4]" l. Ovarian development of colonized CuLexannulirostris after 12 to 14 days following sucrose feedirrg.

Ovarian stage* Larval Locality diet % sucrose IIa IIb II Ia IIIB IVa IVb V Total Brisbane high 25 32.7 35.4 20.9 1.3 0.5 0.7 2.2 6.3 1,915 high J 63.2 30.I 3.9 0.7 1.3 o.7 r52 low 5 100 189 Mildura high 25 42.8 24.8 24.6 2.0 0.2 0.5 0.5 4.6 t,292 * After Christophers(19l l).

or those fed poorly throughout (0%). Ovarioles 2). Female wing length ranged from 3.2 to 3.5 of this latter group showed the least develop- ment of the 3 groups 'fhe examined. insemination rate of 7-12 day old fe- DISCUSSION males from the Brisbane colony was72.8% (250 dissected) whereas 78.8% of 23 I females of This is the first report of autogeny in Cx. similar age from the Mildura colony contained annulirostris and although the rates were gener- sperrn. All spermarhecaeof 5l femalesjudgec ally low, they offer an additional means of sur- to be autogenous (Brisbane 32, Mildura 19) vival for this species.From the data on individ- were positive. ual raft rearings, it would seem that this trait is There was considerable variation in the au- variably distributed throughout siblings of rafts togeny rates of rafts reared individually. For of all sizesand may reach SlVo (or even higher). : Brisbane rafts (n 16), the mean (+ I stan. However, fecundity resulting from sugar fed dard deviation) number of female progeny autogenous females in the Brisbane and Mil- + dissectedwas 77.8 26.1 with an averagCau- dura colonies was much lower (32-48 eggs/raft) + togeny rate of 9.3 9.87o(range 0-30.9%1: lor than that from blood-fed anautogenous devel- : Mildura (n 7), 70.5 + 33.9 females/raft with opment; quoted as 37-355 eggs/raft for the an autogeny rate of 4.8 * 6.9% (range -fhe precursor of the Mildura colony (McDonald et {u-.-19.37o). correlation berween egg raft size al. 19771. (as number of females dissected) and the au- Previous studies of Cx. tarsalis have linked : -0.086). togeny rate was not significanr (R high nutritional status to the expression of au- Of those females judged to be autogenous, togeny (Kardos 1959, Spadoni et al. 1974),and the mean number of mature ova from the Bris- this also seems applicable to Cx. annuliro.stris. bane and Mildura colonies respectively, was Culex annuliro.srri.rreared on high diet and : 32.7 (n: 84) and 39.6 (n 45). Rafts laid bv maintained on high percentage sucrose showed autogenous lemales from the Brisbane colony greater ovarian development than those fed in- contained a mean ol 47.6 eggs (n : 55). Ai- ferior diets. The failure to find autogeny in the tempts to establish an autogenous colony from field populations tested may be due to two fac- this stock failed. tors, (l) their nutritional status was inferior to The ovaries of 997 females reared from 7 that of high diet mosquiroes produced in the field sites throughout Queensland were at laboratory, as indicated by wing length, but Christophers' stage I, IIa or in one case, IIb. more irnportantly, 12) most were uninsemi- However, the insemination rate after 7- l5 days nated. in 0.7 m3 cageswas low, from 0 ro 16% (Table For most mosquitoes, mating does not di-

Table 2' Ovarian development in field collected Culex annulirostris, 7 to l5 days after feeding with rvzo,40/^ SUCIOS€.

Ovarian stage after 7-15 % positive Larval d Locality spermathecae diet IIa IIb Total Dalby 5 sewage Roma 7 nutrients, 98.8 r.2 8l Mitchell l6 Followed by high 72.6 27.4 I02 Tara 6 laboratory diet 87.6 t2.4 r29 Charleville 0 53.6 44.9 l5 69 Townsville 0 97.4 2.6 3ll Kowanyama 0 100 305 Mancn. 1986 J. Av. Mosq. CoN'rnol Assoc. l3

rectly affect the development of the initial egg Dobrotworsky, N. V. 1965. Mosquitoes of Victoria. batch (O'Meara 1979). However, blood-feeding Univ. Press. viruses,in studies of virgin Cx. annulirostris would indicate Doherty, R. L. 1974. Arthropod-borne Australia and their relation to infection and dis- that mating is an important but not an essen- ease.Progr. Med. Virol. l7:136-192. tial factor influencing ovarian development Kardos, E. H. 1959. The effect of larval nutritional all autoge- (Kav 1978). From this and because level on the developrnent of autogeny in colony nous females were mated, we suggest that au- Culex trtrsalisCoq. Proc. Calif. Mosq. Control Assoc. togeny in Cx. annuliro.sfnsis possibly the male- 27:7l-72. induced forrn that has been described by Kay, B. H. 1978. Aspects of the vector potential of O'Meara (1979) for one type of Ae. taeniorhyn' Culex annulirostrir Skuse 1889 and other mosquitoes cftzs (Wiedemann). Consequently, future (Diptera: Culicidae) in Queensland, with particular at Kowanyatna studies of autogeny in field populations of Cx. reference to arbovirus transtnission Ph.D. thesis, University of annulirostris should be made either with insemi- and Charleville. 200 p. nated females or by inoculation of male acces- Queensland, Kay B. H. 1983. Collection of resting adult mos- gland fluid into virgin females. sory quitoes at Kowanyama, northern Queensland and To date, autogeny has been associated with Charleville, southwestern Queensland, J. Aust' few Australian mosquitoes: the malaria vector, Entomol. Soc. 22: l9-24. Anopheleshilli Woodhill and Lee (Sweeney and McDonald, G., I. Srnith and G. P Shelden.1977.Labo- Russell 1973), Ross River virus vector Ae- uigilax ratory rearing of Culev tnnuliroslris Skuse (Diptera: (Skuse) (Sinclair 1976),Cx. pipiens molestusEors- Culicidae).J. Aust. Entomol. Soc' l6:353-358' Mottrarn, P., B. H. Kay and D. S. Kettle. Effect of kal 1: 6*. pipiens Linn.) and Ae. awtraLis (Erich- temperature on egg hatching, development, sur- son) (Dobrotworsky 1965). With respect to vivai and density of ilnmature stages in Culex an-' the vector potential of Cx. annuliroslns, because nulirostrisSkuse. J. Aust' Entornol. Soc. (in press)' are usu- nutrient levels under field conditions O'Meara, G. F. 1979. Variable expressions of au- ally inferior to those in the laboratory (espe- togeny in three mosquito species' Int. J' Invert' cially high diet level), we suspect that expression Reprod. l:253-261. of autogeny would rarely occur in nature. Reeves.W. C., E. L. French, E. N' Marks and N' E' Kent. 1954. Mut'ray Valley encephalitis: a survey ol suspected rnosquito vectors. Arn. J. Tlop. Med' ACKNOWT,EDGMENTS Hyg. 3:147-159. W. C. Reeves.1974' The study was carried out whileJ.D. Edman Spadoni, R. D., R. L. Nelson and Seasonal occut'rence, egg production and blood- was on sabbatical leave at supported by QIMR feeding activity of autogenous Culex tun(lis. Ann. U.S.-Australia Cooperative Science Pro- the Entornol. Soc. Arn. 67:895-902. gram. Sinclair', P. 1976. Notes on the biology of the salt- '\edeszigrla"v (Skuse) in south-east ReferencesCited rnarsh rnosquito, Queensland. Queensl. Nat. 2l: 134- 139. Christophers,S. R. l9l I . The developrnent of the egg Swieney, A. W. and R. C. Russell.1973. Autogeny in follicle in anophelines.Paludism 2:73-88' Anobheles amictus hilLi. Mosq. News 33:467-468'