Field Release of Nonindigenous Parasitic
Scuttle Flies in the genus Pseudacteon
(Diptera: Phoridae) for Biological Control of
Red Imported Fire Ant, Solenopsis invicta,
and Black Imported Fire Ant, S. richteri
(Hymenoptera: Formicidae)

Environmental Assessment

May 1995

Agency Contact:
Ronald D. Hennessey, Ph.D.
4700 River Road, Unit 133
Riverdale, MD 20737-1236
Phone: (301) 734-7839

I. Proposed Action

The Animal and Plant Health Inspection Service (APHIS) of the United States Department of Agriculture (USDA) has received applications (see Appendix 1) from the University of Texas at Austin for permits to release Pseudacteon litoralis Borgmeier, P. solenopsidis Schmitz, P. tricuspis Borgmeier, and P. wasmanni (Schmitz) (Diptera: Phoridae). These parasitic flies are potential biological control agents of the red imported fire ant, Solenopsis invicta Buren, and its close relative, the black imported fire ant, S. richteri Forel (Hymenoptera: Formicidae). Both ants harm man and animals with their vicious stings. S. invicta builds dense mounds, as many as 1,000 per acre, which often interfere with soil cultivation.

Presently, the four aforementioned species of Pseudacteon do not occur in the United States outside the confines of Brackenridge Field Laboratory, University of Texas at Austin, Texas. The applicant proposes to release Pseudacteon flies into the environment by a novel method. First, the flies will be allowed to parasitize red imported fire ants in the Brackenridge laboratory. Entire ant colonies, including parasitized individuals, will then be transported from the laboratory to the field where they will be "planted" near wild populations of fire ants. As the flies complete development and emerge as adults, they presumably will disperse to attack ants in neighboring mounds. It is expected that Pseudacteon species will establish themselves as permanent components of the insect fauna of Texas and reduce red imported fire ant populations by parasitizing worker ants and by interfering with the ants' foraging behavior.

This genus-level environmental assessment (EA) will be used by USDA--APHIS to determine whether or not an environmental impact statement will be required prior to releases of P. litoralis, P. solenopsidis, P. tricuspis, and P. wasmanni in the United States. Similarily, the EA will be used to evaluate future applications for permits to release other South American species of Pseudacteon: P. affinis Borgmeier, P. borgmeieri Schmitz, P. comatus Borgmeier, P. cultellatus Borgmeier, P. curvatus Borgmeier, P. dentiger Borgmeier, P. lenkoi Borgmeier & Prado, P. nocens Borgmeier, P. nudicornis Borgmeier, and P. pradei Borgmeier.

The pending applications for permits to release Pseudacteon species were submitted in accordance with the Federal Plant Pest Act (7 U.S.C. 150aa et seq.) and the Plant Quarantine Act (7 U.S.C. 151 et seq.). This EA was prepared in compliance with the National Environmental Policy Act (NEPA) (42 U.S.C. 4321 et seq.) as prescribed in implementing regulatons adopted by the Council on Environmental

Quality (40 CFR 1500-1509), by USDA (7 CFR 1b), and by APHIS (60 CFR 6000-6005).

II. Purpose and Need for the Proposed Action

The purpose of the proposed releases of Pseudacteon flies is to reduce imported fire ant populations. Populations of indigenous species now suffering from competition with imported fire ants are expected to recover once the pressure of competition has been reduced.

S. invicta ranges over 93 million hectares in the southeastern United States from Texas to North Carolina (Lofgren, 1986; Buren et al., 1974; Porter and Savignano, 1990). It reduces the productivity of pasture land by building numerous large mounds, afflicts man with painful stings, kills small vertebrate and invertebrate animals, and interferes with the electrical industry by building nests in circuit boxes. Negative impacts of S. invicta on indigenous arthropods have been reported by many authors, including Hook and Porter (1990), Hooper (1976), Porter et al. (1988), and Vinson and Sorensen (1986).

Costs of controlling S. invicta through 1989 amounted to about $200 million (Davidson & Stone, 1989). S. invicta is uncontrolled in wild areas and is difficult to control by pesticides on agricultural lands. The ant has no effective natural enemies in the United States.

S. richteri was once widespread in the southern U. S., but it has been displaced by S. invicta over most of its former range. S. richteri survives only in a restricted area of Mississippi (Ross et al., 1987).

III. Alternative to the Proposed Action

The "no-action" alternative to releasing Pseudacteon flies for the control of imported fire ant is to deny the release permit. If the permit is denied, it is probable that pesticides, such as Amdro and Logic, will continue to be used for control of the ants. In some areas pesticide use might be terminated.

Other biological control measures are being developed, e.g., treatment of ant

colonies with pathogenic fungi and nematodes, but they are not presently available, and there is no assurance that they will become available.

IV. Environmental Impacts of the Proposed Action and Alternative

The intended impact of the proposed releases of Pseudacteon flies is the reduction of imported fire ant populations and subsequent recovery of populations of nontarget species.

Plans to release Pseudacteon flies raise the question of possible harm to indigenous ant species. Fortunately, the scientific literature on host-specificity in parasitic scuttle flies is extensive. Solenopsis ants, including S. invicta and S. richteri, are the only known hosts of the 20 or more species of Pseudacteon flies present in South America (Borgmeier, 1962, 1963, 1969; Borgmeier and Prado, 1975; Disney 1991, Porter et al., in press). Genus-level host specificity appears to be a trait of parasitic phorids in general, not just of phorids in the genus Pseudacteon (Borgmeier, 1962, 1963, 1969; Borgmeier and Prado, 1975; Disney, 1991, 1994; Williams and Banks, 1987). Anomalous reports of phorids' attacking more than one genus of ants are either unconfirmed or, for various reasons, considered actually erroneous (Porter et al., 1975).

Generally, parasitic scuttle flies attack only a single species of ant or several closely related species. Williams (1980) and Porter et al. (in press) studied five Pseudacteon species in Brazil, including three of the 14 species listed on page 1. Members of the S. saevissima (Smith) species complex, which includes S. invicta and S. richteri, were the only ants attacked in those studies. Schmitz (1914) reported that an unrelated species of Solenopsis, S. geminata (Fab.), served as host for P. solenopsidis and P. wasmanni in Brazil. The remoteness in time (81 years) of Schmitz's research and the uniqueness of his results suggests a possible misdetermination of the species involved. Gilbert (unpub.), working at the Brackenridge Field Laboratory in Texas, found that P. solenopsidis, P. wasmanni, and two other South American species (P. litoralis and P. tricuspis) parasitized S. invicta and S. richteri but not S. geminata.

All four species of Pseudacteon indigenous to the U.S. attack S. geminata, but not S. invicta or S. richteri (Disney, 1991; Feener, 1987). Other genera of scuttle fly

parasites are equally host-specific. Of the 47 species of Apocephalus listed by Feener and Brown (unpub.), 42 attack only one ant species, and none atacks more than two.

Schmitz's unconfirmed report notwithstanding, studies conducted in South America and the U. S. strongly reinforce the impression that each species of Pseudacteon, whether indigenous or nonindigenous, parasitizes members of a single species complex within the genus Solenopsis. The important conclusions are that (1) if Pseudacteon flies are introduced from South America to the U. S., both species of imported fire ants will almost certainly be attacked, and (2) there is a small chance that a third and more distantly related species, S. geminata, might be incidentally attacked.

The possibility that introduced Pseudacteon flies might attack S. geminata does not necessarily imply a net negative impact on that species; beneficial effects of Pseudacteon must also be weighed. S. geminata was once abundant in Texas, but competition from S. invicta has driven it to the edge of extinction in that state (Porter et al., 1991). If S. invicta were suppressed, S. geminata probably would recover a large fraction of its former abundance despite occasional, incidental attacks by Pseudacteon. Nevertheless, as a precaution, all Pseudacteon species released in the U. S. will first undergo host-specificity tests with S. geminata. Pseudacteon species that accept S. geminata will not be released under this EA, although a separate EA might be written later.

The biological characteristics of Pseudacteon flies preclude any direct impacts on man. Specifically, human health will not be affected, and Pseudacteon cannot become a household nuisance.

Imported fire ants are not utilized as a food source by any threatened or endangered species. The Texas horned lizard, Phrynosoma cornutum, which is listed as a threatened species by the State of Texas, feeds on native ants, principally harvester ants (Pogonomyrmex spp.) (Donaldson et al., 1994).

The "no-action" alternative is to deny the release permit requested by the applicant. In such a case pesticides would continue to be used against imported fire ants. It is important to remark that in some areas, at least, the use of pesticides has exacerbated the problem of S. invicta by killing nontarget ant species which compete with the pest (Summerlin et al., 1977). Pesticides used against ant pests kill many nontarget species (Summerlin et al., 1977), and they are very expensive to

develop and use (Davidson & Stone, 1989). If the use of pesticides were terminated, the killing of nontarget species would cease, but the uncontrolled fire ants would still continue to interfere with agriculture and diminish biodiversity (Porter and Savignano, 1990).

If pathogens become available for use as biological control agents against imported fire ants, they may not be specific enough to avoid harm to nontarget species in certain situations.

The release of nonindigenous scuttle flies in the genus Pseudacteon as biological control agents of imported fire ants is clearly the preferred alternative because of the absence of negative effects and the reasonably high probability of success.

V. References

Borgmeier, T. 1962. Cinco especies novas do genero Pseudacteon Coquillet. Arq. Mus. Nac. (Rio de Janeiro) 27-30.

Borgmeier, T. 1963. Revision of the North American phorid flies. Part I. The Phorinae, Aenigmatiinae, and Metopininae, except Megaselia (Diptera: Phoridae). Stud. Entomol. 6:1-256.

Borgmeier, T. 1969. New or little-known phorid flies, mainly of the Neotropical Region (Diptera: Phoridae). Stud. Entomol. 18:3-90.

Borgmeier, T. & A. P. Prado. 1975. New or little known Neotropical phorid flies, with descriptions of eight new genera (Diptera: Phoridae). Syst. Entomol. 18:191-230.

Buren, W. F., G. E. Allen, W. H. Whitcomb, F. E. Lennartz & R. N. Williams. 1974. Zoogeography of imported fire ants. Jour. New York Entomol. Soc. 82:113-124.

Davidson, N. A. & N. D. Stone. 1989. Imported fire ants, pp. 196-217. In Dahlsten, D. L. & R. Garcia (eds.), Eradication of Exotic Pests: Analysis with Case Histories. Yale Univ. Press, New Haven, CT.

Donaldson, W., A. H. Price & J. Morse. 1994. The current status and future prospects of the Texas horned lizard (Phrynosoma cornutum) in Texas. Texas Jour. Science 46(2):109-113.

Disney, R. H. L. 1991. The fire-ant parasitoids of the Pseudacteon spatulatus complex (Diptera, Phoridae; Hymenoptera, Formicidae). Sociobiology 18:283-298.

Disney, R. H. L. 1994. Scuttle Flies: The Phoridae. Chapman & Hall, London, 467 pp.

Feener, D. J., Jr. 1987. Size-selective oviposition in Pseudacteon crawfordi (Diptera: Phoridae), a parasite of fire ants. Ann. Entomol. Soc. America 80:148-151.

Hook, A. W. & S. D. Porter. 1990. Destruction of harvester ant colonies by invading fire ants in South-Central Texas (Hymen.: Formicidae) Southwestern Naturalist 35:477-478.

Hooper, M. W. 1976. The Effects of the Imported Fire Ant, Solenopsis invicta, on the East Texas Arthropod Community. Thesis, University of Texas at Austin, Austin, Texas.

Krombein, K. V., P. D. Hurd, Jr. & D. R. Smith. 1979. Catalog of Hymenoptera in America North of Mexico. Smithsonian Institution Press, Washington, DC 2,735 pp.

Lofgren, C. S. 1986. The economic importance and control of imported fire ants in the United States. Pp. 227-255 in S. B. Vinson (ed.), Economic Impact and Control of Social Insects. Praeger, New York, NY.

Porter, S. D., A. Bhatkar, R. Mulder, S. B. Vinson & D. J. Clair. 1991. Distribution and denstiy of polygyne fire ants (Hymenoptera: Formicidae) in Texas. Jour. Econ. Entomol. 84(3):866-874.

Porter, S. D. & D. A. Savignano. 1990. Invasion of polygyne fire ants decimates native ants and disrupts arthropod community. Ecology 71(6):2095-2106.

Porter, S. D., H. G. Fowler, S. Campiolo & M. A. Pesquero. 1975. Host specificity of several Pseudacteon parasites of fire ants in South America (Diptera: Phoridae; Hymenoptera: Formicidae). Florida Entomologist 78(1):70-75.

Porter, S. D., H. G. Fowler, S. Campiolo & M. A. Pesquero. Rearing Pseudacteon flies in the heads of Solenopsis fire ant workers (Hymenoptera: Formicidae). Environ. Entomol. (in press).

Porter, S. D., B. Van Eimeren & L. E. Gilbert. 1988. Invasion of red imported fire ants (Hymenoptera: Formicidae): microgeography of competitive replacement. Annals of the Entomological Society of America 81:913-91.

Ross, K. G., R. K. Vander Meer, D. J. C. Fletcher & E. Vargo. 1987. Biochemical and phenotypic genetic studies of two introduced fire ants and their hybrid (Hymenoptera: Formicidae). Evolution 41:280-293.

Schmitz, H. 1914. Die myrmecophilen Phoriden der Wasmannschen Sammlung. Zoologischen Jahrbuchen. Abteilumg fur Systematik, Geographie und Biologie der Tiere 37:509-566.

Summerlin, J. W., A. C. F. Hung & S. B. Vinson. 1977. Residues in nontarget ants, species simplification and recovery of populations following aerial applications of mirex. Environ. Entomol. 6:193-197.

Vinson, S. B. & A. A. Sorensen. 1986. Imported fire ants: life history and impact. Texas A&M University, College Station, and Texas Department of Agriculture, Austin, Texas.

Williams, D. F., & W. A. Banks. 1987. Pseudacteon obtusus (Diptera: Phoridae) attacking Solenopsis invicta (Hymenoptera: Formicidae) in Brazil. Psyche 94:9-13.

Williams, R. N. 1980. Insect natural enemies of fire ants in South America with several new records. Proc. Tall Timbers Conference Ecol. Anim. Control Habitat Manage. 7:123-134.

VI. Preparation and Review

This environmental assessment was prepared by the following scientists (listed alphabetically):

Ronald Hennessey, Ph.D., USDA--APHIS, Riverdale, MD

Lawrence Gilbert, Ph.D., University of Texas, Austin, TX

Edward Vargo, Ph.D., University of Texas, Austin, TX

This document was reviewed by the following scientists (listed alphabetically):

Brian Brown, Ph.D. Natural History Museum of Los Angeles County, Los Angeles, CA
Robin Huettel, Ph.D., USDA--APHIS, Methods Development, Riverdale, MD
Kenneth Lakin, Ph.D., USDA--APHIS, Biological Assessment and Taxonomic Support, Riverdale, MD

Norman Leppla, Ph.D., USDA--APHIS, National Biological Control Institute, Riverdale, MD
Michael Stefen, USDA--APHIS, Domestic and Emergency Operations, Riverdale, MD


USDA--APHIS--PPQ is reviewing applications for permits to release certain species of nonindigenous scuttle flies in the genus Pseudacteon (Diptera: Phoridae) in the United States. These flies are host-specific parasites which are potentially useful in the biological control of the red imported fire ant, Solenopsis invicta Buren, and the black imported fire ant, S. richteri Forel. These ants attack man and kill small wildlife. Mounds of the red imported fire ant often interfere with soil cultivation.

Releases of Pseudacteon species are expected to have no negative impacts on the quality of the human environment. This finding is based on the following considerations:

1. The species of Pseudacteon to be released are parasitic entirely, or nearly entirely, on members of the S. saevissima species complex. Red imported fire ant and black imported fire ant are the only members of this complex present in the United States.

2. Attacks, if any, on an unrelated, indigenous species of fire ant, S. geminata, are likely to be only incidental. In any case, it is expected that S. geminata will benefit from suppression of its main competitor, S. invicta.

3. Pseudacteon flies have no medical or veterinary importance apart from their potential importance in controlling the target pests.

4. Releases of Pseudacteon spp. are expected to have no significant negative impcts on beneficial plants or animals in the United States.

5. No endangered or threatened species listed by the Federal or any State government utilize imported fire ants as a food source. Therefore, releases of Pseudacteon are expected to have no negative impacts on these species.

(signed) May 16, 1995
Charles P. Schwalbe, Ph.D.
Director, Operational Support
Plant Protection and Quarantine
Animal and Plant Health Inspection Service
United States Department of Agriculture

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