Fire Ant Management on Pop-up Target Firing Ranges
Report on Contract No. TX98-E23-04 401-9-5504
May 31, 2000
Prepared by Dr. Michael Merchant, Associate Professor and Urban Entomologist
Texas Agricultural Extension Service

For Dr. Paul E. Powell, Training Site Environmental Specialist, Facilities & Engineering Directorate, Environmental Resources Management Branch, Adjutant General's Department, AGTX-EV, P.O. Box 5218, Austin, Texas 78763-5218; 512/465-5001 ext. 6035; FAX: 512/465-5141; ppowell@ pollution.org

Abstract.
Two granular insecticides were evaluated for the control of red imported fire ants, Solenopsis invicta, in soil surrounding pop-up targets on a Texas Army National Guard firing range in Mineral Wells, Texas. Both fipronil 0.1 G- and tefluthrin 1.5 G-treated plots had significantly fewer numbers of fire ant colonies compared to untreated controls. Numerically fewer foraging fire ants were also found in treated vs. untreated plots, though differences among treatments were not significant.

Prior to treatment, fire ants were observed causing damage to natural rubber and urethane foam components of the pop-up target lifters. Nearly 100 percent of electrical outlet weatherstripping and 22% of the rubber boots on pop-up targets were affected by fire ants.

Treatments were applied to evaluate the ability of a 1% fipronil formulation to protect rubber components from fire ant chewing damage. A 2 x 5 factorial experiment has been initiated to evaluate the long-term effectiveness of soil and component treatment to prevent fire ant damage. Continuation of the research is recommended to complete observations on the effectiveness of these treatments.

Background
The Texas Agricultural Extension Service was first contacted in May, 1998 for assistance in developing a management program for red imported fire ants on National Guard firing ranges. An evaluation of commercially available products was suggested based on earlier research work conducted on commercial, ground based electrical transformers. The project was approved as contract number an TX98-E23-04, and funds were awarded on September 1, 1998. Due to a delay in securing chemical company support, and availability of test materials, a request to extend the project completion date until May 31, 2000 was approved November 1, 1999. This study reports the results of this investigation.

Introduction
The red imported fire ant, Solenopsis invicta Buren, is a persistent pest of ground-based electrical equipment throughout the southern United States (MacKay et al., 1992., Slowik et al. 1997). Recently, several National Guard camps in Texas have reported problems with fire ants infesting and damaging firing range pop-up targets (Merchant, 1999). Camps Maxey (Lamar County, Texas) and Swift (Bastrop County, Texas) report 20 to 40 percent loss of functionality in electronic pop-up targets due to fire ant invasion. Costs of this damage are significant and have resulted in loss of equipment and economic loss. In 1998 the entire pistol range at Camp Bowie was shut down for rewiring, due to damage caused by fire ants in 100 percent of the target lifters. Estimated repair costs were $35,000 with additional costs incurred due to loss of the use of the ranges there (Paul Powell, personal communication, 1998).

Objectives of the study were to identify promising treatment combinations that might reduce the impact of fire ants on ground-mounted machinery, such as pop-up target lifters. Specifically we attempted to determine (1) whether soil insecticide treatments can reduce fire ant foraging and damage around target lifters for extended periods of time; (2) whether an easily-applied treatment can significantly prolong the effective life of the foam weatherproofing used in power outlets and the natural rubber boots used to seal the lifter mechanism.

Materials and Methods
Phase I. Granular site treatment. Fire ant activity was estimated around target lifter sites by counting all active fire ant mounds within an 8 ft ( 2.43 m) radius circle around each site (Figure 1). Mound size was estimated according to a modified rating system based on the work of Harlan et al. (1981). Colonies observed at the site were generally small and rated as 1 (less than 100 ants, mound less than 10 cm diameter), 2 (100 to 1,000 ants, and usually 10 to 40 cm diameter mound), or 3 (1,000 to 10,000 ants, mound usually greater than 40 cm diameter).

In addition to mound counts, assessments were made of foraging fire ant worker abundance on October 19, 1999 and May 31, 2000, respectively. Glass shell vials (1 dram capacity) were baited with two pellets of Seafood Purina® Tender Vittles® cat food, and placed on the soil adjacent to each pad site. After a 2 to 3 hr exposures, vials were collected, stoppered, transported to the laboratory, and frozen. Ants collected in the vials were later counted and identified to species.

Soil treatments were applied to lifter sites on October 19, 1999. Insecticide treatments were applied uniformly to the soil inside a 4.88 m (16 ft) square plot surrounding each lifter vault (Figure 2). Granular formulations of fipronil (Collins et al., 1999) and tefluthrin (Merchant 1998) were applied using a shaker made from a 620 ml (1.3 US pint) Rubbermaid® Servin' Saver bowl with 25 1/8-inch holes drilled in the lid. Soil treatments included:

I. fipronil 0.1 G (low rate) 50 lb product/A (122 g/plot or 0.05 lb a.i./A)
II. fipronil 0.1 G (high rate) 100 lb product/A (244 g/plot or 0.1 lb a.i./A)
III. tefluthrin 1.5 G (low rate) 66.7 lb product/A (161 g/plot or 1.0 lb a.i./A)
IV. tefluthrin 1.5 G (high rate) 133 lb product/A (322 g/plot or 2.0 lb a.i./A)
V. untreated control

Treatments were assigned to lifters according to a completely randomized design with 12 replications per treatment.

Phase II. Component treatment. The second phase of this research has not yet been completed. In Phase II the long-term effects of treatments on the integrity of rubber and foam lifter components (i.e., rubber boots used to seal the lifter armature of targets, and weatherproof seals used on outlet covers) will be evaluated. This portion of the research was begun on 28 March, 2000 when all the old rubber boots were replaced with new boots ordered through the National Guard supply system. In June 2000 a 1 percent suspension of fipronil 10.2% SC in mineral oil will be applied to half of the rubber boots on the test site. In addition, all existing outlet covers will be replaced to allow ongoing assessment of fire ant damage to foam or neoprene weatherproofing on the treated portions of the range.

The impact of treatments on the integrity of foam and rubber components of the target lifters will be evaluated by (1) counting the number of fire ant produced holes in rubber boots, (2) rating the quality and presence or absence of tunneling in foam inserts on power outlets; and (3) monitoring dirt and debris in power outlets. In addition I will evaluate the effects of treatments on cracking or other deterioration of rubber boot and foam inserts.

The experimental design to measure the effects of treatments in protecting rubber and foam components of the lifters will be a 2 x 5 factorial, with treatments randomly assigned to the lifters. A total of 60 lifters is being used with six replicates of each treatment.

Results
Numbers and sizes of fire ant mounds at the Fort Wolters combat pistol range, around target lifter sites, were recorded on April 20, 1999, prior to any treatments being made. Based on this sample, spring fire ant mound density was estimated at approximately 576 mounds per acre, based on an average of 2.37 (± 0.23 SEM) mounds per plot (179 ft²).

In addition, on this date all target lifters were observed for damage to rubber boot seals on lifter armatures and to weatherproofing used on electrical outlets. Approximately 22 percent of the natural rubber boots used to seal the lifter armature exhibited what appeared to be fire ant chewing damage, with 1 to 3 holes per boot (Figure 3). On September 19, 1999, a cloudy day, fire ants were observed clustered on the accordion ridges and edges of about 8 percent (n=84) of the rubber boots, apparently chewing on the rubber.

Ant activity and damage was also evident around the plugs and electrical outlets supplying power to each target lifter. Soil and debris was found in 50 percent of the outlets, and dead ants were found in 38.6% of outlets (n=44). Nearly 100% of the urethane foam electrical outlet cover weatherproofing was damaged by what appeared to be similar fire ant chewing behavior (Figure 4), although ants were not observed damaging foam inserts.

The reason for fire ant attraction to natural rubber or urethane foam is unclear. Similar observations of fire ant chewing on insulation of non-electrified copper wiring have been made by other researchers. Texture of the boots, or oils found in natural rubber, might act as stimulants of fire ant chewing behavior (S.B. Vinson, personal communication).

Because of dry weather during the fall and winter of 1999-2000, mound counts were not attempted until 28 March and 25 May 2000, five and eight months after treatment (MAT), respectively. Mound counts from both sample dates were totaled for the following analysis, although most of the colonies observed and marked on 28 March were not active during the May sample three months later.

There was a significant difference in mound counts between treated and untreated plots when the five and eight MAT mound counts were combined (ANOVA, F=3.88, d.f.=4,55; P<0.0001) (Table 1). Untreated plots had significantly more active fire ant mound activity by eight months after treatment.

Table 1. Effect of various treatmens on numbers of active red imported fire ant colonies around firing range target lifters. Combined mound counts between five and eight months after treatment. Fort Wolters Army National Guard Base, Mineral Wells, Texas. March to May, 2000.

* Numbers within the column followed by the same letter are not significantly different (ANOVA, F=3.88, d.f.=4,55; P<0.0001)

There were significantly fewer fire ant foragers present in vials following a two hour exposure on June 1, 2000 (8 MAT), compared to numbers collected on Oct. 19, 1999, prior to treatment of the test area. Lower numbers of foragers may have been due to seasonal or temperature differences, or due to treatment effects. There were numerically fewer fire ant foragers in treated vs. untreated plots on June 1, 2000, however the differences were not significant (ANOVA, F=0.42, d.f.=4, 55; P>0.796) (Table 2).

Table 2. Effect of various treatments on numbers of foraging red imported fire ants collected in baited glass vials next to firing range target lifters. Fort Wolters Army National Guard Base, Mineral Wells, Texas. March to May, 2000.

*No significant differences among treatments, ANOVA, P>0.05.

Discussion
Fire ant mounds were very common on the combat pistol range at Fort Wolters Army National Guard Base. The pre-treatment estimate of 576 mounds per acre indicates a high population density, and suggests that the area is infested with the multiple queen (pylygynous) form of the red imported fire ant. Although we did not document any failures of lifter units in this study, the effects of fire ant damage on rubber and foam components of the ground-based equipment were apparent.

Fire ant mounds were significantly less common in treated vs. untreated plots at eight months after treatment. However, the number of active mounds were very low in control plots throughout the post-treatment evaluation, possibly due to inter-plot effects or the effects of drought and cooler weather on local fire ant populations. No significant differences among the insecticide treatments were detected by eight months after treatment. Counts of foraging adult ants are generally not highly reliable as indicators of colony density; however, there was a trend for fewer foraging ants to be found in treated lifter plots.

Although results are promising for use of both tefluthrin and fipronil granular insecticides as protectants for firing range equipment, additional time is needed to evaluate the long-term effectiveness of these treatments. In addition, an extended delay in obtaining new rubber boots for all lifters has meant that no data is yet available on the effectiveness of treating rubber boots with 1% fipronil.

A continuation of the project is recommended to allow time to evaluate the long-term effects of these treatments. A two to three year continuation of the project would allow time for fire ant re-infestation of treated and untreated plots, and would permit observations of the potential for fire ants to damage foam and rubber components of the lifter sites.

Literature Cited
Collins, H., A.-M. Callcott, et al. (1999). Evaluation of candidate quarantine treatments for control of IFA in commercial grass sod. U.S. Department of Agriculture/APHIS. Unpublished report, Proj. No. FA01G066. Gulfport, MS.

Harlan, D. P., W. A. Banks, et al. (1981). Large area tests of AC-217,300 bait for control of imported fire ants (Hymenoptera: Formicidae) in Alabama, Louisiana, and Texas. Southwestern Entomologist 6(2): 150-157.

MacKay, W. P., S. Majdi, et al. (1992). Attraction of ants (Hymenoptera: Formicidae) to electric fields. Journal of the Kansas Entomological Society 65(1): 39-43.

Merchant, M. E. (1998). Insecticides for control of red imported fire ants in pad-mounted electrical transformers. Final Report. Unpublished report Texas Agricultural Extension Service, Dallas. May 18, 1998.

Merchant, M. E. (1999). Fire Ant Management on Pop-up Target Firing Ranges. Proposed Research Protocol. Submitted to Paul Powell, October 15, 1999. 3 pp.

Slowik, T. J., H. G. Thorvilson, et al. (1997). Response of the red imported fire ant to magnetic fields in the nest environment. Southwestern Entomologist 22(3): 301-306.

Figure 1. Schematic diagram of firing range target vault showing sampling and treatment zones. Subtracting the area of the target lifter vault (22 ft²) from the overall area of the treated zone (256 ft²) gave a total treatment area of 234 ft².

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Figure 2. Plot surrounding pop-up target marked for evaluation of mound densities (left), and close up view of pop-up target lifter showing outlets and ground-based lifter unit. Fort Wolters Army National Guard Base, Mineral Wells, Texas. Summer, 1999.

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Figure 3. Fire ant chewing damage to rubber boot used to seal the lifter armature on pop-up targets. Holes in boots were judged to be fire ant chewing damage if they were (1) not associated with obvious cracking or weathering, (2) oval to moon-shaped, and (3) having rounded edges. Fort Wolters Army National Guard Base, Mineral Wells, Texas. 1999.

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Figure 4. Urethane foam weatherproofing taken from electrical outlet covers used in pop-up targets at Fort Wolters combat pistol range. Damage to foam presumed due to tunneling behavior by the red imported fire ant, Solenopsis invicta (image approximately life-size).

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