Adverse Assessments of Gambusia Affinis: An

Journal of the American Mosquito Control Association, 12(2):155_166, 1996 Copyright @ 1996 by the American Mosquito Control Association, Inc. FORUM ADVERSE ASSESSMENTSOF GAMBUSIA AFFINIS: AN ALTERNATE VIEW FOR MOSQUITO CONTROL PRACTITIONERS' HENRY R. RT]PP 1440 Mohawk Road, North Brunswich NJ 0g902_I4I l ABSTRACT' Adverse opinions on the introduction of Gambusiaaffinis for the control of larval mosquitoes are reviewed. The sourcesspan a period of some 59 years un"d"o-" from a variety of sources. The principal opposition to the introduction of G. ffinis clmes from ichthyologists, although some mosquito researchers have expressedconcerns about the environmental impJct oi placing *rJ fisrr in habitatsto which it is not native. Questionsconcerning the appropriatenessofusing the fish are presented. Although mosquito research and control per_ ical Control of Mosquitoes, Laird (19S5) pointed sonnel have been almost unanimous in their ap_ out that biocontrol of mosquitoes had been al_ proval of the use of Gambusia affinis for mos_ most exclusively concerned with G. affinis pior quito control, members of the ichthyological to commercial production of Bacillus thurin_ community have viewed introduction of tho fish giensis subspecies israelensis. Early successes into nonnative habitats with alarm because of with the fish had led to widespread dispersal. real and potential damage to these ecosystems. Laird pointed out concern by the World Health This paper presents a brief review of "recommendation idverse Organization leading to a that opinions so mosquito control personnel can have G. affinis not be introduced into new areas but another perspective to consider when planning that indigenous species be researched and to utilize the fish outside its native habitat. used." He noted application ofpredatory agents Meisch (1985) published a l4-page chapter on "destruction ^ should not result in of tirese aI_ Gambusia affinis affinis in the basic text for ready-present natural enemies of mosquitoes.', mosquito control workers, Biological Control of Although there are many larvivorous fish, Gam_ Mosquitoes. Writing from b mosquito corrt ol- busia has been the backbone of biocontrol for perspective, Meisch included a section on ..Nes_ one-quarter of a century, and Laird remarked ative Aspects," although these negativ" "ori_ that any other biological control agents could ments were vitiated by insertion of positive also have adverse impacts. The effect on non_ statements about Gambusia. Bay (19g5) wrote a "Other target organisms should be reduced. Thus. Laird chapter on Larvivorous Fishes', in this recommended cost/risk/benefit studies as an es_ same book. In the concluding chapter of Biolog_ sential part of any control program and conclud_ ' ed, most realistically, that no adverse impacts In the August 1995 issue of ttre AMCA Newsletter. would mean no mosquito control. President John Edman suggested that we might have a 1967 Bay had reviewed positive torum section in the Journal of the AMCA to promote ]n and neg_ ative aspects of the use scientific debate. Fortuitously, a controversiai manu- of Gambusia and later (1972) script was received from Henry Rupp, entitled ,.Ad_ reviewed opposition to use of Gambusia verse assessments of Gambusia affinis: an in West Africa, citing the anti-Gambusia alternative "most feel- view for mosquito control practitioners." This manu_ ings of ichthyologists.,, script appeared to be ideal for such a forum. Com_ Another source, long familiar to mosquito ments about Mr. Rupp's manuscript "A were solicited control workers, is guide to the use of the lrom a number of mosquito control or wildlife soe_ mosquito fish, Gambusia afinis, for mosquito cialists who were asked to give their views on the pios control" by Scholdt et al. (1972). Scholdt or cons of Mr. Rupp's contention that the use of dam_ "the warned. that impact busia for mosquito control may have more negative of the fish on t}te aquat_ rc envlronment effects than positive ones. These comments ,roi, *" cannot be underestimated as being published with the above paper. The response of there is good evidence that the indiscriminate our readers to a Forum section and suggestions for use of mosquito fish can be as detrimental as the topics would be appreciated.-R. frture Al Ward, nd- misuse of pesticides." Many of the same sentiments were echoed bv r55 156 Jouwar oF THEAMERIcAN Moseurro CoNrnor Assocrmot Vor-. 12, No. 2 "Time Laird (1977) who wrote, has proved that on Gambusia in Ecology and Evolution of Live- mosquitofish eventually became harmful in bearing Fishes, where they state: some areas to which they were introduced half "In summary, mosquito fish a century ago-the harm ranged from eating the almost invariably present a multitude of problems when introduced eggs of economically desirable fish, to endan- beyond their native range and offer no real compen- gering rare indigenous species." Later, in 1988, satory or biological control advantages. The species Laird cited Miura's work in the rice fields of should not be used as a larvivore, with native spe- California as indicative of the lack of adverse cies much preferable in that role whenever possible effects on one environment, an environment (e.g. Lloyd 1986). Mosquitofish are far too aggres- Harrington (personal communication) referred to sive and predatory to be indiscriminately spread "artificial." as Laird (1988) cited L6gendre's throughout the world without recognition of dangers 1937 article in the Bulletin Economique Indo- to native biota. An international ban on their use as a control agent is biologically chine, pointing out that the threat to indigenous appropriate and war- ranted." fish from Gambusia predated Myers's 1965 article, which referred to events of the mid-l93Os, What are the reasons presented for this con- but seemed unaware of Sweetman's The Biolog- demnation? Let us look at some of the evidence ical Control of Insects (1936), which had pre- Courtenay and Meffe present in their review of ceded L6gendre by a year and would have been the literature dealing with the adverse affects of more readily accessible to mosquito control the use of Gambusia. practitioners in this country. Howeveq Laird re- The first complaint raised is that Gambusia is "Too minds us, much should not be expected, not really that effective in mosquito control and though, of such indigenous fish in natural waters that better control has been achieved with native of high taxonomic diversity," and indicated, in species (Table I ). As far back as 1949 Bates was "The relation to Aplocheilus panchax, omnivorous noting, success of practical operations fish can maintain themselves well in nature with- along these lines [biological control] has not out mosquito larvae, and Gambusia is indeed an been very remarkable." ln 1967 Harrington "very omnivore. He also cited Russian feeling that (personal communication) said, few en- "the general effectiveness of this fish has been tomologists have sound evidence of the alleged disappointing." efficacy of Gambusia where it has been intro- Speaking of biocontrol programs, Laird duced." (1988) commented on use of Aplocheilus latipes In Australia, Allen (1989) remarked on Gam- in Russia following tests of larval consumption busia's lack of efficacy in mosquito control, and rates of the fish in aquaria. in 1993 Dennis C. Haney of the National Bio- logical Survey of the U.S. Department of the "It "I is submittedthat biocontrol introductions of this Interior wrote (personal communication), kind, based upon a mosquito larvivore that is very think you will find that there is little or no evi- probably of far more catholic tastesthan univariate dence for Gambusia being particularly effective laboratory experimentscould reveal, are only likely in controlling mosquito larvae. In fact, almost to prove successful where mosquito production is all the evidence indicates that Gambusia is no unusually high in rather short-lived larval habitats better at controlling larvae than are native fish." harbouring a limited flora and fauna; or in more Recognizing there is testimony complex aquaticecosystems where preliminary hab- on both sides itat manipulation is undertakento give, for example, of the issue and Gambusia may not be so uni- Aplocheilus unrestrictedaccess to dense concentra- versally successful as we have been led to be- tions of larval Culicidae." lieve, let us tum to what ichthyologists consider a more serious issue. The failure to effect larval Service (1983) noted adverse environmental control is a concern of the mosquito control effects resulting in increased mosquito produc- community, but Gambusia's impact on nontar- tion from the use of Gambusia, and in 1995 he get organisms affects a broader community of reaffirmed his doubts about the value of Gam- interests. busia in control for disease prevention purposes. The concern with environmental impacts goes In 1985 Mahmoud, in a study of the efficacy of back more than half a century when in 1936 Gambusia for malaria control in the Sudan, con- Harvey Sweetman warned in his pioneering The cluded Gambusia, although effective in canals Biological Control of Insects: "an and ditches, was not efficient mosquito con- "Finally, it should always be held in mind that trol measure during the peak season of malaria " the introduction of any foreign animal is apt to cause transmission. repercussionson the native fauna in unexpected These caveats are mild compared to the opin- ways. Gambusia has been spread far and wide in ion presented by ichthyologists Courtenay and anti-mosquitowork, frequently in ignoranceofvalu- Meffe (1989) in the conclusion to their section able native species. Gambusia affinis and G. hal- JUNE 1996 FoRtrM: Aovense AssEssMENTsoF GAMBUSTA t57 Table l. Reports of unsuccessful mosquito control by Gambusia affinislholbroati (from Courtenay and Meffe !9891; see this publication for reference citations). Locality Comments Reference Australia ft lr *g quito control than some native fishes. "I Australia believe their effect on mosquitoes has been negli- Lake (1971) gible. " california Mosquitofish can increase mosquito populations by Moyle (1976) eliminating other mosquito predators.

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