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Management of the European Fire Ant in Eastern Maine

Dr. Eleanor Groden & Dr. Francis A. Drummond

University of Maine

306 Deering Hall
University of Maine
Orono, ME 4469

(207) 581-2989

(207) 581-2969

eleanor.groden@umit.maine.edu

Executive Summary

The European fire ant, Myrmica rubra L., has become a serious problem in many sites along the coast of Maine, a few in Massachusetts and one site near Buffalo, NY. The densities of this aggressive, stinging ant have increased dramatically and its invasive front has expanded in the past several years. It is literally driving people out of their yards, as well as negatively impacting native fauna. At present many residents and businesses are using over-the- counter ant insecticides with little or no success in managing the European fire ant. This is particularly problematic in that treated areas include parks, areas around residences, athletic fields, schools, daycare centers and public building where human exposure is considerable.

This pest has followed the pattern typical of invasive species: a prolonged period of adaptation with moderate population increase after establishment, followed by an exponential increase in density and an increase in the rate of geographic spread. Infestations have spread from two documented locations in Maine in 1952 to more than 20 communities in 2002. The widespread distribution of this ant in Europe suggests that climatically it will not be limited to current infested areas in the northeast. The primary means of natural spread of this ant is via budding colonies on the ground. New infestations in noncontiguous areas are the result of human transport of ants in soil, mulch, and potted plants. For this reason, educating homeowners, nursery, landscape, and greenhouse business persons, and public officials about this invasive pest is the most important step to take to limit its further spread.

THE GOALS OF THIS PROJECT are two-fold and address the needs of multiple stakeholders: 1) develop a “least toxic” strategy for managing current infestations to reduce the risk of pesticide exposure, and 2) raise awareness within the nursery/greenhouse industry and general public of the problems associated with this ant and the need to prevent further spread.

Objectives

  1. Develop least toxic management strategies for M. rubra that maximizes natural mortality.
  2. Raise awareness of the biology, ecology, potential spread and methods of managing M. rubra, by developing and distributing user-friendly materials to homeowners and green industry members.

Justification

1) Develop least toxic management strategies for M. rubra that maximizes natural mortality:

In the past ten years, the European fire ant, Myrmica rubra, has become a significant problem for nursery and landscape businesses, residents, tourists, and tourist related businesses in several coastal areas in Maine including Acadia National Park on Mt. Desert Island (Fig. 1). This ant has become established in large colonies in disturbed and natural areas around residences and commercial buildings, aggressively defending its territory. It readily stings humans (Fig. 2 & 3) and animals. At present many residents and businesses are using excessive amounts of over-the-counter general-purpose insecticides with little or no success in managing the European fire ant. This is particularly problematic in that the areas around residences, athletic fields, schools, daycare centers and public building - are also areas where human exposure is considerable. This proposal seeks to develop an effective pest management program for M. rubra that is based upon the use of least toxic insecticides that maximizes the activity and persistence of natural biological controls occurring in Maine soils.

Many of Maine’s coastal communities are within fragile ecosystems that are susceptible to even small degrees of pesticide pollution. This objective is aimed at reducing the risk and effects of pesticide pollution by integrating tactics: properly timed and applied reduced risk insecticides and natural control. Development of an effective pest management program will reduce exposure of people to highly toxic insecticides and reduce deleterious effects on non-target organisms.

2) Raise awareness of the biology, ecology, potential spread and methods of managing M. rubra, by developing and distributing user-friendly materials to homeowners and green industry members: Thus far M. rubra populations in Maine have exhibited the typical pattern characteristic of many invasive, exotic species: a prolonged period of adaptation with moderate population increase after establishment, followed by an exponential increase in density and an increase in the rate of geographic spread (Shigesada and Kawasaki. 1997). In addition to increases in density witnessed within many locales in the past decade, M. rubra also appears to be spreading more rapidly: from 2 locations in Maine in the 1950s to more than 20 locations along Maine’s entire coast as of 2002 (Groden et al. 2002). Known pestiferous populations also exist in coastal Massachusetts and at a nature preserve outside Buffalo, NY. Given that the geographic distribution of this ant in its native range spans from the United Kingdom in Western Europe to central Asia and from Scandinavia to the Black Sea (Collingwood 1958, Seifert 1988), it is unlikely that climatic factors alone will limit the spread of these populations in the northeastern U.S.

The biology of M. rubra and its pattern of infestation suggests that their primary means of spread is via colony budding into adjacent areas, or via human transport of nests in infested materials (soil, decaying logs, potted plants, etc.). A student working in Groden’s laboratory brought in ants that were stinging employees when they encountered them in container plants being repotted at a wholesale greenhouse facility in southern Maine. They proved to be M. rubra. We have also confirmed that the first infestation in Maine to become established more than twenty miles from the coast resulted from the planting of shrubs purchased from a nursery in an infested coastal community. (This inland infestation has now persisted through four winters.) It is likely that infested container plants brought to Maine from Europe for planting in gardens of coastal estates are responsible for some of the original introductions in the early half of the 20th century. (The first reported occurrence of the ant in the US was at an arboretum (Wheeler 1908).) Subsequent movement of plants, soil, mulch, and fill have spread M. rubra to new areas. For this reason, educating people about this invasive pest is the most important step to limit its spread.

Overall Summary

There have been no studies conducted on the life history or population biology of M. rubra in the US. European studies indicate that the colony structure of M. rubra is polygynous (multi-queen colonies) and that they overwinter as colonies of queens, workers, and larvae (Elmes and Wardlaw, 1981). We have found between two and 39 queens per nest and 218 to 1500 workers per nest in Maine (Groden and Drummond, unpublished data).

Myrmica rubra is a common species associated with mesic soils in grass habitats throughout its native range and quite often is found nesting in association with tree stumps (Brian, 1952). We have found that M. rubra uses a variety of nesting substrates throughout the season and exhibit a highly polydomas nature. The density of M. rubra nests sampled at two infested sites in Acadia National Park in 2002 averaged up to 1.2 and 1.4 nests/m2 (with a range of 0 -5 nests/ m2). Weekly monitoring of nesting substrates demonstrated that M. rubra colonies, which likely consist of several satellite nests, bud and move their nests frequently. Abraham and Pasteels (1980) reported that M. rubra, in Europe, will move their nests when microclimatic conditions are unsuitable.

Few studies have been conducted on the natural enemies of M. rubra. In Europe, Lepidopteran larvae of the genus Maculinea are predators of M. rubra larvae (Thomas, 1984), but few species of parasites, predators, or pathogens have been described from ants other than Solenopsis fire ants and leaf-cutting ants (Kermarrec et al., 1986; Laumond et al., 1979). Solenopsis spp., being Myrmicine ants, are closely related to M. rubra, and share many of the same attributes including aggressiveness, polygyny, and high reproductive capacity. During the past several decades surveys for natural enemies of fire ants have been made in South America and the southern U.S. (Jouvenaz et al., 1977; Jouvenez, 1986). A limited number of organisms have been identified and some, such as the fungi Beauveria and Metarhizium, are nonspecific to Southern imported fire ants (Stimac et al., 1989).

In July 2002 we sampled cadavers in middens associated with M. rubra nests at three sites on Mt. Desert Island, ME and recovered both Beauveria bassiana and Metarhizium anisopliae infections. These fungi were grown on nutrient agar and bioassays against M. rubra workers. All isolates of the fungi produced significantly greater mortality and subsequent sporulation than the controls after 11 and 14 days (Table 1). Subsequent collections from middens at other infested sites in the area yielded between 5.3 to 25% of the cadavers collected on any date sporulating with either M. anisolpiae or B. bassiana (Table 2). No parasitoids, nematodes or other pathogenic fungi were observed.

Since the European fire ant is not considered pestiferous in Europe, research has not been conducted on its management. However, much relevant research has been conducted on control of southern imported fire ants, with particular focus on insecticide tactics (Williams et al., 2001). Environmental problems resulting from the use of persistent insecticides for fire ant control have lead to the development of more environmentally friendly insecticides. Field trials have demonstrated that hydramethylnon in a corn grit bait (Amdro®) is very effective for control of southern imported fire ant. Ginsberg et al. (2002) has recently shown that Amdro® has some potential for management of M. rubra in Maine.

In the 1980s and 1990s, new least toxic insecticides including those that act as insect growth regulators (IGRs) have shown efficacy against fire ants (Banks and Lofgren, 1991; Dress and Barr, 1998). Methoprene, when applied to fire ant nests, stops egg laying by the queens, disrupts metamorphosis, causes cannibalism of pupae by workers, and eventual death of the colony (Vinson and Robeau 1974). Drees and Barr (1998) have shown that methoprene performed very well in field tests, reducing the number of colonies over time. However, 40-60 days were required for most colonies to be destroyed. In our field trials where individual M. rubra nests were treated with Extinguish® (methoprene), reduction of M. rubra foraging occurred at 21 days post treatment compared with the control. However, due to the high density of surrounding nests, and the slow acting nature of the material, neighboring ants quickly recolonized the plots. Our trial does indicate a downward trend at three weeks post Extinguish® treatment. The USDA-ARS Areawide Program for Suppression of Fire Ants in the southeastern US includes treatments with reduced rates of Extinguish® plus Amdro®. Amdro® decreases the foraging ant population and provides immediate reduction of populations, while Extinguish® provides long-term reduction of colonies.

An older, very low toxicity insecticide, boric acid, incorporated into a bait has also been found to be effective against fire ants (Klotz et al., 1997). Klotz and Williams (1996) found that using 1% boric acid in a 10% (by wgt) sucrose solution provided optimum control of Florida carpenter ants (Klotz and Moss 1996). Low boric acid concentrations (1% and less) have been found to be more effective at reducing Argentine ant and S. invicta populations because higher concentrations can be repellant (Klotz et al. 1997, Klotz et al. 2000) and kill ants too quickly (Stringer et al. 1964). A slow rate of kill is necessary to assure that the forager ants transfer the poison to the rest of the colony. Similar positive results with baited boric acid solutions have been demonstrated for other pestiferous ants, however, continuous exposure to baits over a period of ten weeks provided greater reduction or elimination of queens, brood and workers compared to a shorter duration exposure of 3 days (Klotz et al. 1996).

We conducted two preliminary trials in 2002 with a single exposure to a baited boric acid
(Terro Ant Killer II®, Senoret Chemical Co., Inc.). In both trials, an initial reduction in the density of foragers was seen after treatment with boric acid. However, treated areas in these trials were very small (7 x 7 m2 plots), and M. rubra in surrounding areas moved into the plots quickly. Based on the findings of Klotz and Williams (1996), it is possible that the boric acid concentration in the Terro product (5.6%) is too high, killing the foragers before it is effectively distributed. Our laboratory studies have shown that 1% boric acid provides >95% mortality in M. rubra workers after 21 days. We hypothesize that a continuous exposure of this lower concentration may provide an effective least toxic control strategy.

Boric acid treatments have also been shown to enhance activity of entomopathogenic fungi. Exposure of German cockroaches to low concentrations of boric acid has been shown to synergize infection by M. anisopliae (Zurek et al. 2002). Although the mechanism is not known both topical applications of dust and 0.1% boric acid in drinking water decreased the LT50 for M. anisopliae from 10 days to 5 and 6 days, respectively. Given that we isolated M. anisopliae and B. bassiana from M. rubra populations in Maine and that infection appears to be common, boric acid treatments could potentially trigger natural epizootics providing more effective long term pest suppression.

The PIs currently have a grant, funded by the National Park Service, supporting two graduate students working on applied ecological investigations of M. rubra at Acadia National Park. We also have funding from USDA/APHIS to conduct a state-wide survey to determine the extent of M. rubra infestations in Maine. The Maine Agriculture Center has provided matching funds for this proposed project. Dr. Frank Drummond has a partial appointment with the UMaine Cooperative Extension, which will facilitates support the publication of fact sheets for M. rubra. The research activities proposed to the PESP will enable us to extend our current research and develop a comprehensive IPM program that focuses on least-toxic control tactics.

Approach and Outcomes

1) Develop least toxic management strategies for M. rubra that maximizes natural mortality.

Evaluate least toxic insecticides:
We will trial the following treatments for effective control of the ants in Year 1: 1) Amdro®, 2) Extinguish®, 3) Extinguish® followed by Amdro®, 4) baited boric acid, and 5) untreated control. Because of the mobility of M. rubra colonies, we have found single nest treatments to be inadequate for evaluating the efficacy of control materials. Therefore, it will be necessary to evaluate the efficacy of the treatments in large plots. Treatments will be applied at recommended rates (1.5 lbs / acre for both Amdro® and Extinguish®) in early June in replicated (4x) 0.05 ha plots using a hand-held broadcast spreader for treatments 1-3. Boric acid bait stations as described by Klotz et al. (1998) will be made and placed at a density of one per each 10 X 10 m2 area within the plot. Bait stations will be continuously supplied with boric acid/sucrose solutions for ten weeks. A completely randomized block design will be used with pre-treatment measures of ant foraging strength monitored with sucrose baited vials (10 placed in the interior of each plot) used as a covariate. After application(s) of treatment materials all plots will be monitored biweekly for worker activity throughout the summer by deploying 10 sucrose baited traps/plot for a one hour time period. In September, six randomly selected nests will be excavated per plot and the number of brood (immatures), workers, and queens will be counted and recorded. ANCOVA will be used to assess treatment differences.

Assessment of natural mortality:
Live and dead ants will also be sampled from each plot on a monthly basis by collecting 100 foragers leaving nests and 50 cavaders in middens. Live ants and cadavers will be surface sterilized before being dissected and examined microscopically for signs of parasitism or infection by protozoans or bacteria (following procedures from Lacey, 1997). Cadavers collected from middens will be placed in individual wells of 12 well plates, maintained at high humidity and monitored regularly for emergence of parasitoids, entomopathogenic nematodes, or sporulation of fungi. ANOVA will determine if natural mortality is enhanced by the applications.

Refining least toxic management strategy:
In Year 2, different timing (early spring vs. late spring and summer) and frequency of applications of the most efficacious material from Year 1 trials will be further evaluated to develop a strategy which reduces M. rubra populations while maximizing natural mortality. Treatments will be applied and assessed as described for Year 1.

2) Raise awareness of the biology, ecology, potential spread and methods of managing M. rubra, by developing and distributing user-friendly materials to homeowners and green industry members:

Fact sheets:
Two fact sheets will be developed. The first, to be developed at the beginning of the project in YEAR 1 will include information about M. rubra’s biology, ecology, and potential spread that we have gathered in the past two years of research. This first fact sheet will also include a tear-off section at the bottom for clients to fill out and send back to the project with specimens they suspect are M. rubra. This will allow us to identify new infestations and track spread. The second fact sheet will be printed at the end of the project (YEAR 2) and will update the information on the first fact sheet and include recommendations for management that result from our research. Distribution: In collaboration with UMaine Cooperative Extension and Maine Dept. of Agriculture colleagues, these fact sheets will be made available to homeowners and industry members at a number of venues including the Maine Master Gardener Program, Garden and Flower Shows, Maine’s 16 county extension offices, Maine Landscape and Nursery Association’s annual meeting, New England Grows, and at the University of Maine Cooperative Extension’s GardenPro. Brochures will also be distributed to nurseries by the Maine Dept. of Agriculture’s nursery inspectors, providing an opportunity to educate workers likely to encounter this problem.

Website:
M. rubra information will be incorporated as a fact sheet into the University of Maine Cooperative Extension’s website (http://www.umext.maine.edu/topics/pest.htm) in YEAR 1. The website will allow for frequent updating of new management methods in YEAR 2.

Impact Assessment

The goal of the proposed research is to develop more environmentally sound management options for the European fire ant in eastern Maine, and raise public awareness of this invasive pest to slow its rate of spread. The initial success of the proposed program will be evaluated by the successful reduction in M. rubra populations measured in field trials, and in the utilization of education products developed. The distribution of fact sheets and the number of web hits will be recorded to document how many people access the information, and an on-line comment form will allow both homeowners and green industry members to pose questions and make comments about M. rubra. The ultimate success of this project will be seen in the reduced reliance of homeowners, businesses, and park managers in infested areas on broad spectrum insecticides, and in a reduction or slow in the spread of this pest. We will survey the quantity of insecticide used by both the National Park Service and Municipal Park managers on Mount Desert Island in Maine, prior to this research. A similar inventory will be conducted after completion of the study at one year following the release of the final fact sheet with IPM recommendations. We will continue to monitor new M. rubra infestations throughout the state through reports to extension agents and comments sent to our website.

Literature Cited

Abraham, M. and J.M. Pasteels. 1980. Social behavior during nest-moving in the ant Myrmica rubra L. (Hym. Form.). Insectes Sociaux 27(2): 127-147.

Banks, W.A. and C.S. Lofgren. 1991. Effectiveness of the insect growth regulator pyriproxifen against the red imported fire ant (Hymenoptera: Formicidae). J. Entomol. Sci. 26: 331-338.

Brian, M.V. 1952. The structure of a dense natural ant population. J. Anim. Ecol. 21: 12-24.
Collingwood, C.A. 1958. The ants of the genus Myrmica in Britain. Proc. R. Ent. Soc. Lond. (A) 33: 65-75.

Dress, B.M. and C.L. Barr. 1998. Fire ant trails: news from the Texas fire ant research and management plan. Nov. 2: 2.

Elmes, G.W. and J.C. Wardlaw. 1981. The quantity and quality of overwintered larvae in five species of Myrmica (Hymenoptera: Formicidae). J. Zool. Lond. 193: 429-446.

Fernandez, S., E. Groden, J.D. Vandenberg, and M.J. Furlong. 2001. The effect of mode of exposure to Beauveria bassiana on conidia acquisition and host mortality of Colorado potato beetle, Leptinotarsa decemlineata. J. Invertebr. Pathol. 77: 217-226.

Ginsberg, H.S., C. Lussier, D. Manski, and G. Ouellette. 2002. Management of the stinging ant, Myrmica rubra, using a baited formulation of hydramethylnon, 1997. Arthropod Management Tests, 27: Report J3.

Groden, E., F. A. Drummond, J. Garnas, and S. Yan. 2002. Preliminary Investigation of theEuropean Fire Ant in Maine. Proceedings of the Acadian Entomological Soceity Annual Meeting, Machias, ME. Abstract p. 12.

Jouvenez, D.P., G.E. Allen, W.A. Banks, and D.P. Wojcik. 1977. A survey for pathogens of fire ants Solenopsis spp. in Brazil. Florida Entomol. 63: 275-279.

Jouvenez, D.P. 1986. Diseases of fire ants: problems and opportunities. Pp. 327-338 In: C.S. Lofgren and R.K. Vander Meer (eds.). Fire ants and leaf-cutting ants biology and management. Westview Press, Boulder, CO.

Kermarrec, A., G. Febvay and M. Decharme. 1986. Protection of leaf-cutting ants from biohazards: is there a future for microbiological control? Pp. 339-356 In: C.S. Lofgren and R.K. Vander Meer (eds.). Fire ants and leaf-cutting ants biology and management. Westview Press, Boulder, CO.
Klotz, J.H. & J.I. Moss. 1996. Oral toxicity of a boric acid -sucrose water bait to Florida carpenter ants (Hymenoptera: Formicidae). J. Entomol. Sci. 31:9-12.

Klotz, J.H., and D.F. Willliams. 1996. New approach to boric acid ant baits. IPM Practitioner 18(8): 1-4.

Klotz, J.H., D.H.. Oi, K. M. Vail and D.F. Williams. 1996. Laboratory evaluations of boric acid liquid bait on colonies of Tapinoma melanocephalum, Linepithema humile, and Monomorium pharaonis (Hymenoptera: Formicidae). J. Econ. Entomol.

Klotz, J.H. , K.M. Vail, and D.F. Williams. 1997. Toxicity of a boric acid-sucrose water bait to Solenopsis invicta (Hymenoptera: Formicidae). J. Econ. Entomol. 90(20): 488-491.

Klotz, J.H., L. Greenberg, and E.C. Venn. 1998. Liquid boric acid bait for control of the Argentine ant (Hymenoptera: Formicidae). J. Econ. Entomol. 91(4): 910-914.

Klotz, J.H., L. Greenberg, C. Amrhein, M.K. Rust. 2000. Toxicity and repellency of borate-sucrose water baits to Argentine ants (Hymenoptera: Formicidae). J. Econ. Entomol. 93(4): 1256-1258.

Laumond, C., H. Mauleon, and A. Kermarrec. 1979. Donnees nouvelles sur le spectre d’hotes et la parasitisme der nematode entomophage Neoplectana carpocapsae. Entomophaga 24: 13-27.

Lofgren, C.S., W.A. Banks, and B.M. Glancy. 1975. Biology and control of imported fire ants. Ann. Rev. Entomol. 20:1-30.

Pereira, R., J. L. Stimac, and S.B. Alves. 1993. Soil antagonism affecting the dose-response of workers of the red imported fire ant, Solenopsis invicta, to Beauveria bassiana conidia, J. Invertebr. Pathol. 61 (2): 156-161.

Seifert, B. 1988. A taxonomic revision of the Myrmica species of Europe, Asia Minor, and Caucasia (Hymenoptera: Formicidae). Abh. Ber. Naturkundemus Gorlitz, 62 (3): 1-75.
Shigesada, N. and K. Kawasaki. 1997. Biological invasions: theory and practice. Oxford Univ. Press, NY, NY.

Stimac, J.L., S.B. Alves, and M.T.V. Camargo. 1989. Controle de Solanopsis spp. (HYmenoptera: Formicidae) com Beauveria bassiana Vuill. em condicoes de laboratorio e campo. An. Soc. Entomol. Brasil 18: 95-103.

Stringer, C.E., C.S. Lofgren, and F.J. Bartlett. 1964. Imported fire ant toxic bait studies: evaluation of toxicants. J. Econ. Entomol. 57: 941-945.

Thomas, J.A. 1984. The behavior and habitat requirements of Maculinea nausithous (the Dusky Large Blue Butterfly) and M. teleius (the Scarce Large Blue) in France. Biol. Conserv. 28: 325-347.

Vinson, S.B. and R. Robeau. 1974. Insect growth regulator: effects on colonies of the imported fire ant. J. Econ. Entomol. 67: 584-587.

Wheeler, W.M. 1908. A European ant (Myrmica levinodis) introduced into Massachusetts. J. Econ. Entomol. 1(6): 336-339.

Williams, D.F., H.L. Collins, and D.H. Oi. 2001. The red imported fire ant (Hymenoptera: Formicidae): An historical perspective of treatment programs and the development of chemical baits for control. A. Entomol. 47(3): 146-159.

Zurek, L., D.W. Watson, and C. Schal. 2002. Synergism between Metarhizium anisopliae (Deuteromycota: Hyphomycetes) and boric acid against the German cockroach (Dictyoptera: Blattellidae). Biological Control 23: 296-302.

Timetable

2003 - 2004

September - December
Objective 2: Develop initial factsheet on M. rubra and develop webpage.

January - April
Objective 2: Distribute factsheets at green industry meetings, garden shows, and other listed outlets.

May - August
Objective 1: Conduct year 1 field trial.

2004 - 2005

September - December
Objective 1: Process samples and analyze data Objective 2: Update and maintain website. Distribute M. rubra information at fall industry and public meetings.

January - April
Objective 2: Update and maintain website. Distribute M. rubra information at spring industry and public venues.

May - August
Objective 1: Conduct year 2 field trial. Process samples and analyze data. Objective 2: Update factsheet and website with research results.

Major Participants

Cooperators:

Project Budget

Funding Request
Funding Requested Other Funding Total Funding
$39,290
$22,603
$61,893

Project Duration: Sept 1, 2003 to August 31, 2005

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