Journal of the Americctn Control Association, 20(3):2g6_291,2OO4 Copyright A 2OO4by the American Mosquib Control Association, Inc.

LABORATORY EVALUATION OF THE PREDATION EFFICACY OF NATIVE AUSTRALIAN ON (DIPTERA: CULICIDAE)

TIMOTHY P HURST, MICHAEL D. BRowNI eNo BRIAN H. KAY

Australian Centre International for and Tropical Health and Nutrition at the eueensland Institute of Medical pO Research, Royal Brisbane H

ABSTRACT. The introduction and establishment of fish populations can provide long-term, cost-effective mosquito control in habitats such as constructed wetlands and ornamental . The p.idution efficacy of 7 native Brisbane freshwater fish on I st and 4th instars of the freshwater arbovirus vector culex annulirostris was evaluated in a series of 24-h laboratory trials. The trials were conducted in 30-liter plastic carboys at 25 + l"C urder a light:dark cycle of l4:10 h. The predation eflcacy of native crimson-spotted (Melanotaeniidae), cluboulayi Australian smelt Retropinna semoni (Retropinnadae), pacific blue-eye pseudomugil (Atherinidae), signfer fly-specked hardyhead Craterocephalus stercusmLtscarum (Atherinidae), hretail gudgeon Hypseleotris gttlii (Eleotridae), empire gudgeon Hypseleotris compressa (Eleotridae), and estuary percilet Am- bassis marianus () was compared with the exotic eaitern mosquitofish Getmbusia iolbrooki (poe- ciliidae). This environmentally damaging exotic has been disseminated worldwide and has been declared noxrous in Queensland. Melanotaenia duboulayi was found to consume the greatest numbers of both lst and 4th instars of Cx. annuliro.t/ri.t. The predation efficacy of the remaining Australian native species was comparable with that of the exotic G. holbrooki. With the exception of A- marianu^s, the maximum predation rates of these native species were not statistically different whether tested individually or in a school of 6. Based on these data, M. duboulayi, H. compressa, and A. marianas warrant further investigation as biological control agents in pilot field trials.

KEYWORDS Biological control, predation efficacy, native fish, Cul.ex annulirosrrls, schoolinq

INTRODUCTION mosquito control by Australian native species do not provide any real evidence, mostly citing anecdotal ln 1925, Gambusia holbrooki Girard was intro- examples (Cooling 1923, Hamlyn-Harris 1929). duced into Queensland as a mosquito-control agent There is evidence that native R. semoni and M. du- (Lloyd 1986). This species has subsequently caused boulayi include a higher percentage of mosquito lar- considerable environmental damage by displacing vae in their diets than G. holbrooki (Lloyd 1986). native Australian fish species through competition Also, P. signifer are reported to be equally as effec- and direct predation (Arthington et al. 1986, Ar- tive as G. holbrooki in preying on mosquito larvae thington and Marshall 1999, Ivantsoff and Aarn in saltmarsh pools (Morton et al. 1988). Addition- 1999). Therefore, alternative biological control aIIy, north Queensland populations of eastern rain- agents to G. holbrooki are required to effectively bowfi sh, M elanotaenia splendida splendida (Peters) control mosquito populations with minimum impact and C. stercusmuscarum, were efficient predators on local ecosystems. of mosquito larvae in the laboratory (Russell et al. In Brisbane, stream fish assemblages are predom- 2OOr). inantly comprised of small insectivorous and omniv- Although there are a number of native Australian orous species such as crimson-spotted rainbowfish, fish species that are potentially more effective mos- Melanotaenia duboulayi (Castelnau); Australian quito-control agents than G. holbrooki, careful smelt, Retropinna semoni (Weber); flyspecked har- evaluation of local Brisbane species is required. dyhead, Craterocephalus stercusmuscarum (Gin- Some investigators have compiled lists of desirable ther); firetail gudgeon, Hypseleotris galii (Ogllby); characteristics or presented steps for evaluating ef- empire gudgeon, Hypseleotris compressct (Krefft); ficacy of local fish species as larvivores (Ungu- Pacific blue-eyes, Pseudomugil signiftr Kner; and reanu et al. 1981, Cech and Moyle 1983, Ahmed estuary perchlet, marianus Giinther (Ar- et aI. 1988). In addition to a number of other fac- thington 1992). Small, native fish species such as tors, they recommend quantitative bioassays of these are ideal candidates for mosquito control, and field-collected fish to directly assess their relative while these species have often been cited as effective efficacy in consuming mosquito larvae. Tradition- mosquito-control agents (Hoese et al. 1980, Ivantsoff ally, the predation rate of individual fish is tested 1980, McDowall 1980, Munro 1980, Lloyd 1986), in the laboratory and the resulting consumption as- little rigorous testing has been done. Most reports of sumed to be the maximum consumption rate of this species. However, there is also evidence to suggest I Present address: FMC (Chemicals) Pty. Ltd., Crop and that the predation efficacy of individual fish of Speciality Division, PO Box 329, Hamilton Central, some species may increase when feeding in a Queensland 40O7, Australia. school (Baird et al. 1991, Ranta and Kaitala 1991, SepreNasen2004 PREDATToNop NarrvE FtsH oN MosQutrops 287

Foster et al. 2001). A number of the species tested, General such as R. semoni, M. duboulayi, A. marianus, and P. signifer, are known schooling species (Ivanstoff The laboratory methods applied in this study are 1980, McDowall 1980, Munro 1980) and in an ef- a modification of those detailed by Panicker et al. fort to determine maximum predation rates of each (1985), Homski et al. (1994), and Russell et al. species, schools of fish in addition to individuals (2001). Whereas Homski et al. (1994) ran predation were evaluated. Our study, therefore, provides the trials in 2.5-liter glass jars, we utilized 30 liters of essential laboratory assessmentto determine which tap water held in white plastic containers filled to species are worthy of field assessment. Culex an- a depth of 0.5 m. The increased volume/water depth nulirostis Skuse is a major vector of arboviruses was chosen to allow species to forage at the appro- in Australia and breeds in permanent and temporary priate water levels according to previously stated freshwater (Russell 2002). preferences: bottom (H. compressa), midwater (1L galii), surface (R. semoni, G. holbrooki), or all lev- els (M. duboulayi, A. marianus, P. signifer, and C. 'fhe MATERIALS AND METHODS stercusmuscarum). tap water was aerated, treated with Prime' water conditioner (Seachem Collection and maintenance of local Laboratories Inc, Stone Mountain, GA) to remove freshwater fish chlorine and chloramine compounds lethal to fish, Adult M. duboulayi (mean total length and SD and left to stand for 24 h before use. Individual test -r of 74.30 -r 3.57 mm), R. semoni (46.88 3.49 specimens were removed from the holding aquaria mm), C. stercusmuscarum (4O.46 4- 5.74 mm), 1L and distributed randomly into test containers. The + galii (36.61 + 7.13 mm), and H. compressa(58.76 trials were conducted at 25 loC under a light: 'r 4.35 mm) were collected from Kholo Creek, dark cycle of 14:10 h. For each trial, the fish were Brisbane (27'32'5, 152'51'E). Subadult M. dubou- then held in the containers fbr a 24-h acclimation layi (4O.31 + 2.06 mm) were collected from Little period to standardize hunger levels and ensure all Nerang Dam, Gold Coast (28'09'5, 153'17'E). gut contents had been evacuated and known num- Pseudomugil signifer (34.31 -+ 2.23 mm) and A. bers of Cx. annulirosrris added. After 24 h. the fish marianus (49.63 + 3.65 mm) were collected from were removed from the containers, the total length the brackish reaches of the North Pine , Bris- and wet weight for each individual recorded and bane (21"17'5, 153"01'E). A Department of Pri- remaining larvae (dead or alive) were counted and mary Industries permit (General Fisheries Permit consumption calculated. PRM02079 F) was required for collection of G. holbrooki (3 I . l8 + 5. 13 mm) from Kedron Brook, Brisbane (27"24' S, I 5 3"03'E). Individuals were col- Predation elficacy on 4th instars of lected using a 40- X 40-cm, L2-mm-mesh scoop Cx. annulirostris net (Jones's Tackle Pty. Ltd., Brisbane, Australia) Two hundred 4th instars of Cx. annulirostris and 25- x 25- x 46-cm, 2-mm-mesh bait traps were added to each of 7 treatment and 3 control (Mossop's Tackle Pty. Ltd., Brisbane, Australia). Males females of each fish species Specimens were transported to the laboratory in containers. and possible aerated l5-liter buckets. For those species collected were tested separately to determine differ- predation from freshwater, 4 glliter of table salt was added to ences in efficacy between sexes. Both the water to prevent bacterial and parasite infection adult and subadult M. duboulayi were tested. If all and reduce the effects of stress,osmotic imbalance, larvae were consumed by a species within the ini- and surface damage during transport (Legget 1995). tial test, the individuals were retested, using incre- In the laboratory, fish were maintained in 42- x ments of 50 larvae until the maximum predation 34- X 2-cm glass aquaria equipped with biological rate had been determined. Data was also expressed filtration at25 + l'C. Fish were fed Wardley's trop- as number consumed per gram of body weight. ical food flakes* (Wardley Corporation, Secaucus, NJ) and mosquito larvae daily and were acclimated Predation efficacy on lst instars of for at least 14 days prior to experimentation. Cx. annulirostris

Mosquitoes One thousand lst instars of Cx. annulirostris were added to each of 5 treatment and 3 control The lst and 4th instars of Cx. annuliroslrls used containers and tested over 24 h for predation by in this study were reared from egg rafts obtained males of the 8 species. Again, when all larvae were from a colony maintained at the Queensland Insti- consumed, numbers were increased in increments tute of Medical Research (QIMR). The colony was of 1,000 larvae until the maximum predation rate originally established in 2001 from Cx. annuliros- was determined. Data was also expressed as num- tri.s adults collected from Boondal. Brisbane. ber consumed per gram of body weight. JounNel or rur AvsnrcaN Mosquno CoNrnol AssocrerroN Vor. 20, No. 3

Effects of intragroup competition predation lr on qnqn ln efficacy o qnn la< of native fish c{$O\O O\€i I UEA *vO For comparison FF with individual predation rates, 8ed zz schools of 6 male fish were tested under the same a (,u aqctcl |:qq t* conditions as individual tests using 4th instars holO\oO NO\O\ ts of E r\OF-\O o|,-A Cx. annulirostri.r. To allow for possible increased f- ts predation rate due to schooling, each group of 6 t: fish was offered 12 times qqqolnnat\ the mean number of lar- o o0! *-O$$\aci*\O la, F6*mola-.lN+n ti vae eaten in individual predation trials. E:-b0'i Each ex- E X periment t: was replicated 5 times using different fish E,l5 la., in each trial. The number of larvae cQ > consumed per dcOtj 6'A&6A'bKdo: t^ fish per school was then calculated based on the +oi --;\dGi dd; -i t{ >-i-o (a€N\OoOSr)Oc.le.i assumption that individuals within each school con- o 1,5 lr: sumed equal numbers of larvae. t-

r)r)FclOOSiO\ l$ IB () 6dr;cjoi+dr;c; Statistical methods i;NO@a-tiOt6 k ls To corect for natural larval mortality in au) treat- Q I '1:a:--^-?::ta ments, predation efficacy data was normalized with o 'hm+dbn666hdb t: respect to the controls using Abbott's formula (Ab- o.-i\ori od6i6o--' SS$64--Nt=+ I ,r bott 1925). The effect of fish species on predation olF .ro tt efficacy was tested using a l-way analysis of var- la iance with all pairwise comparisons analyzed by LX ?: n+s\o\ooomr|c.l to Tukey honestly O\cioO6+-0Or)O significantly different test (Tukey o b0: volvcloo-r)\o (SigmaStat THbO 1953) for Windows, version 2, Jandel tr Y'- ts Corporation). The effect of fish gender and intra- E^B j\ o0. cO > Ir group competition on predation efficacy within spe- o9 290-e4n- lq qdaE cies was B> +t o O\+t\O\€ido6 lJ{ tested using a /-test. Raw data was square- 2'- +\oooi 6i d.-Jr-- IH\ OrNr)@Or)ic.) root transformed to satisfy the assumptions of o t3E normality and equal variance. tP p tEs iE r tF a @o@cnor)+r)€ lz' RESULTS : !. 6 f- al o\\ f'- 6I-- b^.9 * ol c.l vo c.l v6 ct l;E ts^ lc R Predation efficacy bg 3- los on 4th instars of tra Cx. annulirostris In k 99!.q9 a t-* Of the 8 atcatr-F-$c.rca*oj species evaluated, only G. holbrooki (t AX c.i j Fr \d.r oi di r; + : -5, : < : r)S:j-*OFN\O\O df 12, P 0.001) and H. galii (t 3.49, o9, NF teq : d.t. 12, P : 0.005) exhibited gender differences t! F cE in predation efficacy (Table 1). Female G. hol- l--c.)$$0O\OtncncO brooki consttmed greater numbers of Cx. annuli- d oo: V r) C'.1 o O\ \O t'- C'l ci IF; ic.'*+vreld!1 tus rostris than males, whilst male 1L galil consumed 6 E b.10 ItoF greater numbers than did females. When reanalyzed E^B cO > relative to body weight, no such differences were dC/l! l;i o +t o +cjoqqq\aqq Itra apparent. When the predation rates of males and mN-c.lciOO\Or) z-- OOlt--oOn\OOiO lHtx females were combined for each soecies. adrJlt M. l]{ d duboulayi consumed significantly ttlgher numbers IUUS o to !{ than all other species tested and, not surprisingly, l'-clt--F-N\OOl€i to B.: a o-odc.i+\ciddF Itr-L q subadultM. duboulayt (F:51.99, df :8, P < N-NO I dv: ta .: 0.001) (Table 1). Subadult M. duboulayi consumed o tra lot! significantly higher numbers than all remaining C) --9r_!-q9 t-uw ll,. , species except R. semoni, which consumed signif- E o F-oO\o.iO\O\Oi0O 6d++oi .-.ioir;d icantly higher numbers than P. signiftr and H. galii $o$niOoIr+ ca+ l9sa (F : 51.99, df : 8, P < 0.001). The predation rate l: !; o lot€ of G. holbroofti was comparable with the remaining le a.s 6 nativespecies evaluated (F:51.99, df:8, P IEES lo:t < 0.001). .i IEE} q o lc< n Relative to body weight (Table l), subadult M. GA duboulayi consumed significantly higher (F : - S 4 { oi\N ';.-t 26.28, dt : 8, P < 0.001) numbers of 4th instars la

Table 2. Comparison of the mean number (Abbott's adjusted t*SDl) of first instar Culex annulirostris consumed by 7 native and 1 introduced fish species versus the mean number consumed per gram of body weight.'

Mean number (aSD) Fish species Mean number (+SD) per g body weight

Ambassis marianus 744.8,r (348.0) 565.2qd (31l.6) C rate roc ephalus ste rcusmus carum 855.9b." (268.5) |,475.5" (526.r) Hypse leotris compressa 402.Od (217.3) 236.Od (133.5) Hypseleotris galii 829.6d (128.6) 1,052.l.d (363.r) M elanotaenia duboulay i (subadult) 7,t64.s" (628.4) 9,708.5b (r,239.O) Pseudomugil signiftr 581.5"d (32s.1) 984.2.t (593.6) Retropinna semoni 863.6o. (236.9) 1,328.8" (392.1) Gambusia holbrooki 1,648.1b (414.8) 15.026.5^ (s,328.9)

rColum means followed by the same letter were not significantly different (P > 0.05)

anus, H. galii, C. stercusmuscarum, adult M. du- of 4th instars of Cx. annulirostris larvae consumed : boulayi and P. signiftr. Retropinna semoni and G. by male M. duboulayi (t = 0.87, df : 10, P - holbrooki were also efficient larvivores, consuming 0.41), R. semoni (t : 1.87, df = 9, P : 0.1), P. significantly higher (F :26.28, df : 8, P < 0.001) signifer (/ : 1.15, df : 9, P : 0.28), C. stercus- numbers of 4th instars of Cx. annulirostris than H. muscarum (t : -2.O8, dt : 17, P : 0.053), 1L compressa, A. marianus, H. galii, and P. signifer. galii (t: -1.03, df : 10, P = O.327), and H. Craterocephalus stercusmuscarum, H. galii, and compressa (F : 3.65, df : 10, P : 0.09). Individ- adtit M. duboulayi consumed significantly (F : ual A. marianus consumed significantly higher 26.28, dt : 8, P < 0.001) higher numbers of 4th numbers of 4th instars of Cx. annulirostris larvae instars of Cx. annuliroslris than either H. compres- within a school than when tested alone (r : -5.1, sa or A. marianus (P < 0.001). d.f.:10.P<0.001).

Predation efficacy on lst instars of DISCUSSION Cx. annulirostris This is the lst evaluation of Australian native Subadult M. duboulayi were found to be the most fish as mosquito predators utilizing G. holbrooki as effective predator of Cx. annulirostris lst instars, a comparison. The predation efficacy of various consuming significantly higher numbers than all species of Gambusia have been evaluated prior to other speciestested (F: 83.85, df :7, P < 0.001) their use in numerous mosquito-control programs (Table 2). Conversely, H. compressa were the least worldwide (Menon and Rajagopalan 1977, Yadav effective predator of lst instars of Cx. annulirostris, et al. 1992, Homski et al. 1994). In comparison, consuming significantly less (F = 83.85, df = 7, P native species performed favorably, some con- < 0.001) than M. duboulayi, R. semoni, and C. ster- sumed greater numbers of mosquito larvae, i.e., M. cusmuscarum. Pseudomugil signiftr, H. galii, and duboulayi arld R. semoni, while others demonstrat- A. marianus were intermediate to, but not statisti- ed similar predation rates to those of the introduced cally different from, these 2 groups. The introduced species. G. holbrooki consumed significantly higher num- Yadav et al. (1992) and Jayasree et al. (1992) bers (F: 83.85,df :7, P < 0.001) thanH. com- used laboratory tests for evaluating the predation pressa, P. signifer, H. galii, and A. marianus. efficacy of candidate biological control agents, pre- Subadult M. duboulayi consumed significantly senting a predatory index, which was defined as the higher (F : 68.75, dt : 7, P < 0.OOl) numbers of number of larvae consumed per gram of body 1st instars of Cx. annulirostris larvae per gram of weight. As size-related sexual dimorphism has been body weight than all other native species tested. noted in both G. holbrooki and H. galii (Hoese et Hypseleotris compressa was least effective, con- al. 1980), use of the predatory index was consid- suming significantly less (F :68.75, df :7, P < ered appropriate in evaluating performance. 0.001) than M. duboulayi, C. stercusmuscarum, and In addition to high predation efficacy, species R. semoni. The introduced G. holbroofti consumed that do not discriminate on the basis of instar are significantly higher numbers (F : 68.75, df :7, P favored for operational use. In this case, popula- < 0.001) than all other species tested. tions will feed continuously without periods of prey switching or starvation due to the absence of a pre- ferred instar. However, instar discrimination may Effects of intragroup competition on predation still be desirable if the preference is for later instars, efficacy of native as a predilection for early instars may fail to reduce Intragroup competition within a school of fish mosquito densities below that caused by expected (Table 1) did not significantly increase the number natural mortality of the population (Service 1995). JoupNel op rHe Arr,rsnrcel Moseuno CoNrrol AssocrerroN VoL. 20, No. 3

For instance, the survival rate of Cx. annulirostris cient larvivore when schooled and may have po- in man-made without introduced predators tential if released into appropriate habitats. was estimated to be l 17o(McDonald and Buchanan However, this species is reported to feed predomi- 198 1). Also, if a biological control agent consumes nantly on aquatic plants (Arthington 1992), and early instars in preference to the later ones, the re- given a choice may show preference for aquatic sulting reduced densities of older larvae may lessen plants over mosquito larvae in the field- interspecific competition, thus allowing more lar- Populations of nontarget macroinvertebrates, vae to pupate and give rise to adults (Service 1995). serving as alternative food sources, may reduce the Although all species consumed both lst and 4th intensity of mosquito predation by fish (Hoy et al. instars of Cx. annuliroslrls, 2 species, H. compressa 1972, Hurlbert et al. 1972, Kramer et al. 1988, Lin- and P. signifer, showed a possible preference fbr den and Cech 1990, Walton and Mulla 1991, Blau- one instar over another. Hypseleotris compressa is stein 1992). Although A. marianus fed readily on reported to prefer larger, coarser food (Hamlyn- mosquito larvae in our laboratory trials, gut content Harris 1929) and this was evident in the results, as analysis (Arthington 1992) indtcated that this spe- this species was the least effective predator of lst cies is predominantly vegetarian in nature. Cooling instars of Cx. annulirostis. In contrast, P. signifer (1923) noted P. signifer is less likely to feed on was the least effective predator of 4th instars of Cx. mosquito larvae in nature than when observed in a annulirostris but consumed similar numbers of lst laboratory (Cooling 1923). In tropical north instars as other species. The small mouthgape of P. Queensland, M. splendida is known to prey on tad- signifer results in up to lo0-fold increases in han- poles of the green tree , Litoria caerulea dling time for prey items longer than 3 mm (Booth (White) (Hylidae) (Russell et al. 2001). In New et al. 1985). The mean length of 4th instars of C_r. South Wales, H. compressa, H. galii, and P. sig- annulirostris in the current study was 6.3 + 0.8 nifer reportedly prey on green and golden bell mm. Melanotaenia duboulayi consumed high num- , Litoria aurea (Lesson), eggs, fry, and tad- bers of both instars, as did A. marianus, R. semoni, poles if sufflciently hungry (Pyke and White 2000). C. stercusmuscarum, and H. galii. In Brisbane, H. compressa and H. galiihad ingest- At least one species, i.e., A. marianas, showed a ed large numbers of chironomid rather than mos- statistically significant increase in predation effica- quito larvae, as determined by their gut contents cy when used as a school. Efficacy for other school- (Arthington 1992). These findings indicate thar the ing species, such as M. duboulayi, R. semoni, C. next essential step in our study should be to find stercusmuscarum, A. marianus, and P. signifer did the response to alternative prey. not change. This present study demonstrates that predation Although all species consumed mosquito larvae, rates of some Australian native fish are equal to and the current data and available literature indicate that in some cases, i.e., M. duboulayi, greater than Gam- some species have less potential for use in mos- busia species evaluated in this and similar studies quito-control programs than others. For instance, worldwide (Menon and Rajagopalan 1977, Yadav while R. semoni and C. stercusmuscarum were ef- et al. 1992, Homski et al. 1994). currenrly, M. du- ficient larvivores, both showed poor survival during boulayi, H. compressa, and A. marianus are the collection and transport (McDowall 1980, Russell strongest candidates for biological control programs et al. 2O0l). In captivity, high levels of mortality against Cx. annulirosrrls, especially for introduc- were also noted in the current study and stocks for tion into constructed wetlands and ornamental testing were difficult to collect due to these species' lakes. patchy distributions. Conversely, M. duboulayi, H. galii, and H. compres,sa are hardy species, partic- ACKNOWLEDGMENTS ularly 1L compressa, which were able to tolerate very poor water quality (Cooling 1923, Hamlyn- The authors would like to thank the Mosquito Hanis 1929). Also, M. duboulayi and H. galii arc and Arbovirus Research Committee Inc. for finan- highly adaptable to laboratory and field conditions cial support. Peter Ryan (QIMR) reviewed this and reproduce readily in aquaria and experimental manuscript. Ray Leggett (Natural History Consul- ponds, making them easy to culture and distribute tant, Brisbane) provided useful discussion and (Hamlyn-Harris 1929, Hoese et al. 1980). However, guidance, whereas Kay Marshall (QIMR) supplied H. galii displayed differences in predation efficacy mosquito larvae. between sexes, indicating that they may have less potential as mosquito-control agents than some of REFERENCES CITED the other species. The other gudgeon tested, 1L compressa, displayed some preference for later in- Abbott WS. 1925. A method of computing the effective- ness of an insecticide. stars, which may prove beneficial in mosquito-con- J Econ Entomol 78: 265-267. Cited in Chapman,GA. 1995. Sea urchin sperm cell trol programs. In contrast, the predilection of p. .rig- test. In: Rand GM, ed. Fundamentalsof aquatic toxi- nifer for early instars is considered a disadvantage cology: effects,environmental and risk assessment for a mosquito-control fate, agent. 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