By Eric Benson, Pat Zungoli, Melissa Riley and Donny Oswalt
A recent study at Clemson University provides insight on the impact of fire ant baits exposed to commonly used pest control products, cigarettes and gasoline, and the loss of effectiveness.
The red imported fire ant unfortunately is a fact of life for most residents in the Southeast U.S. The ability of fire ants to bite, sting and build large mounds make this species a significant pest. A 1998 telephone survey of residents in 809 South Carolina households found that 69 percent of the residents had a problem with fire ants in their yard with 33 percent reporting that fire ants restricted family activities in the yard. About 93 percent of the respondents said it was important to control fire ants (Miller et al. 2000).
One of the most common control strategies is the use of baits. Many factors impact the effectiveness of bait products, including competition with other food sources, age of the bait, timing and environmental conditions when bait is applied. How a bait tastes, known as palatability, is an important factor that can influence bait acceptance and effectiveness. Active ingredients in baits must be at concentrations that do not cause the targeted ant to avoid or take less bait than what is needed for control. For example, Klotz et. al (1997) reported that the amount of bait consumed by fire ants was related to the amount of boric acid in the bait. Increasing the boric acid in the bait made it less palatable.
External compounds also may make baits repellent or unpalatable. Bennett et al. (1988) stated that baits stored with other pesticides or volatile chemicals may become tainted with chemical residues and be rendered repellent. However, no studies have documented or evaluated the contamination of currently used fire ant baits by other products commonly used or stored with baits by pest management professionals. The purpose of our study was to: 1) determine if common fire ant bait products could become contaminated when stored or used in areas where baits are exposed to substances such as gasoline, fertilizer, insecticides or cigarette smoke; 2) evaluate the impact of these contaminants on bait acceptance by red imported fire ants in the field; and 3) evaluate potential fire ant bait contamination on service trucks and storage at a pest control firm.
LABORATORY TRIAL. Three commonly used fire ant baits, Amdro (0.73% hydramethylnon [AI]; BASF Corporation), Ascend (0.011% abamectin [AI]; Whitmire Micro-Gen Research Laboratories Incorporated) and Maxforce (1.0% hydramethylnon [AI]; The Clorox Company) were exposed to potential contaminants. The baits were shipped in sealed containers, directly from the manufacturers.
The contaminants included the insecticides Orthene Fire Ant Killer (50.0% acephate [AI]; Ortho Consumer Services), Cyren (44.6% chlorpyrifos [AI]; Cheminova) and Tempo 2 (24.3% cyfluthrin [AI], Bayer Corporation). Other contaminants included Marlboro Lights cigarette smoke (Philip Morris Incorporated), unleaded gasoline (89 octane, Ameranda Hess Corporation) and fertilizer (10-10-10, Wetsel Seed Company).
Baits were placed in foil-lined, plastic boxes covered with lids. Bait granules were spread on the bottom of the boxes. For most treatments, a small aluminum pan containing 2 grams of a contaminant was placed in the center of each box for 48 hours.
Cigarette smoke contamination was achieved by placing five lit cigarettes on an aluminum pan in the center of the box. Four holes were drilled in the lid and six holes were drilled in the sides of the box. After the cigarettes burned completely, the holes were covered with tape and boxes were left undisturbed for 48 hours. After exposure, vials were filled with treated baits and stored in a standard freezer until analyzed.
Gas chromatography/mass spectroscopy (GC/MS) analysis was used to determine contamination by comparing volatile components of baits, contaminants and contaminated baits. Analysis of baits exposed to fertilizer were identical to unexposed baits indicating that no contamination had occurred. Contamination did occur in baits exposed to Orthene Fire Ant Killer, Cyren, Tempo 2, cigarette smoke and gasoline.
FIELD TRIALS. Based on the results from the GC/MS analysis, the three baits were exposed to Orthene Fire Ant Killer, Cyren, Tempo 2, cigarette smoke and gasoline and were tested in the field. Only one bait product was tested on any given red imported fire ant mound. Treatments consisted of one uncontaminated bait (control) and five samples of the same bait product contaminated individually with each of the contaminants.
Nine replicates of each bait and the same bait product contaminated, were evaluated. Mounds of similar size (8 to 15 centimeters in diameter) and activity were selected. Trials were initiated within one hour after sunrise. Each treatment consisted of a small, plastic petri dish (60 by 15 millimeters) containing 4 to 5 grams of bait. Pre-trial weights were recorded for each dish. Each mound had a circle of six petri dishes of bait randomly placed within 5 to 10 centimeters from the edge of the mound. Petri dishes remained in place for one hour.
After one hour, petri dishes were removed and covered with lids and left in the sun to kill any remaining ants. Dead ants were removed and bait was weighed. The difference between pre- and post-feeding weight was calculated and used for analysis.For all baits, the uncontaminated controls were preferred by fire ants over all contaminated samples. For Amdro, control bait was significantly preferred over smoke, Tempo 2, Cyren and gasoline contaminated baits. For Maxforce, control bait was significantly preferred over Cyren, gasoline and Tempo 2 contaminated baits. For Ascend, the control bait was significantly preferred over Cyren and Tempo 2 contaminated bait.
FIELD SURVEY. To evaluate fire ant bait contamination at a pest control company, a mid-size firm was selected. The company had four trucks for general pest control and one truck for termite baiting.
All five trucks carried either Amdro and/or Maxforce baits for fire ant control. The trucks were open bed style with commercial grade camper shells. Equipment and a variety of pest control insecticides and formulations were kept in the open beds near the ant baits. Only the termite truck carried extra gas in the bed for power augers.
The company also had a chemical storage facility. Gas was not stored in this area, but a wide variety of insecticides and formulations were stored on open shelves near bulk containers of Amdro and Maxforce. The facility was temperature controlled, but not ventilated.
On two occasions, fire ant baits were collected from the company. The first collection occurred in the spring. The baits sampled had been purchased three to six months earlier. Four Amdro and four Maxforce bait samples were collected from each truck.
In the summer we provided the company additional Amdro bait to be stored on their trucks and in their chemical storage facility for one month. We asked the technicians to use and store the baits as they normally did during the test period. After one month, eight samples of Amdro were collected.
Samples were evaluated using GC/MS analysis and compared to our baseline analysis of uncontaminated Amdro and Maxforce. Of the 16 samples collected, nine (56 percent) showed some level of contamination, indicating that volatile compounds had been absorbed by some of the baits. For the spring survey, three of the four Amdro samples were contaminated and two of the four Maxforce samples were contaminated. For the summer survey, four of eight Amdro samples were contaminated after one month of storage.
CONCLUSION. Fire ant baits are commonly used because they provide a relatively safe, practical and effective method for fire ant control. However, data from our study indicate it is possible to easily contaminate fire ant bait with volatile insecticides and products such as gasoline and cigarette smoke, which reduces bait palatability.
Understanding the ease of contamination and the impact of contaminants on bait acceptance by fire ants can help reduce contamination, increase effectiveness and ultimately, save money.
At Clemson University in Clemson in South Carolina, Eric Benson is an associate professor and Pat Zungoli is a professor in the department of entomology. Melissa Riley is an associate professor in the department of plant pathology. Donny Oswalt is a graduate research assistant in the entomology department.
References:
Bennett, G. W., J. M. Owens and R. M. Corrigan. 1988. Truman’s Scientific Guide To Pest Control Operators. Edgell Communications. Duluth, MN. p. 495.
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 (2):488-491.
Miller, S. E., M. S. Henry, B. J. Vander Mey and P. M. Horton. 2000. Averting-Cost Measures of the Benefits to South Carolina Households of Red Imported Fire Ant Control. J. Agric. Urban Entomol. 17(3): 113- 123.