Note: See the technical review of this report.
Given the shortcomings of individual mound treatments, this study is limited to a comparison of the two existing types of broadcast treatments, most commonly marketed as Amdro and Logic. These bait products are based on theknowledge that both the larval stage and adult ant stores liquid food and regurgitates it to feed other ants, including the queen. The baits include slow-acting chemical agents which are passed along until they reach the queen and kill her to eradicate the colony.
Application requirements of Amdro and Logic. All bait treatments should be applied when ants are active and the ground temperature is between 7005 and 9505 F. The ground must be dry, with no rain forecast for the next few hours [7]. Amdro is designed for broadcast application on pastures, range grass, lawns, turf, and noncrop areas [8:122] at a rate of 1 to 1-1/2 pounds per acre [1]. It may also be distributed around the base of an individual mound at a rate of 5 tablespoons per mound, not to exceed a total of 1-1/2 pounds per acre, including any bait broadcast in the area [1].
Logic is recommended for controlling fire ants around homes, office buildings, city utilities, on roadsides, in parks, cemeteries, school yards, and on golf courses at a rate of 1 to 1-1/2 pounds per acre. For best results, both mound and broadcast treatment are recommended [3]. The application rates of Amdro and Logic are the same. Both products are designed primarily as boardcast treatments on turf but individual mount treatment is recommended in conjunction with the broadcast method.
Environmental hazards of Amdro and Logic. Environmental hazards can be assessed on the basis of toxicity of the product, the range of organisms affected, and product accumulation in the environment.
Toxicity. The toxicity of a substance is generally expressed in terms of its lethal dosage, the amount of the substance which, when ingested, results in the death of 50% of the test animals [2]. Lethal dosage is abbreviated as LD50. The lower the LD50 number, the more toxic the substance (5). The LD50 is 1131 mg per kg of body weight for the active ingredient in Amdro [8:122]. The LD50 of the active ingredient in Logic is 9220 me per kg of body weight [8:49]. The active ingredient in Amdro is approximately eight times more toxic than that of Logic. However, a lethal dosage ratio of 1131 (Amdro) to 8813 (Logic) more accurately compares the difference in toxicity between the two products because Amdro contains 0.88% active ingredient and Logic contains 1% active ingredient. As purchased, the commercial product Amdro is approximately seven times more toxic than Logic.
In practical terms, a lethal dosage for a medium-sized dog (weighing approximately 35 pounds) is more than 3 pounds of the active ingredient of Amdro. Since a one pound bag of the product contains only 1% active ingredient, the entire amount of Amdro purchased to treat a 10-acre camp ground would not constitute a lethal dosage for a medium-sized animal. Smaller animals are in greater danger of ingesting a lethal dosage. However, non-fatal health effects, such as diarrhea, can result for any size animal from consumption of a tablespoon of Amdro [6]. Logic, by virtue of its lower toxicity level, would need to be consumed at a much higher rate to produce comparable effects.
Organisms affected. In addition to killing fire ants, Amdro kills harvester ants. At a higher concentration, the active ingredient in Amdro kills cockroaches. Amdro may attract pets and rodents [8:123] and, if consumed in sufficient amounts, can kill pets. Amdro is toxic to fish (1). When used as recommended, Logic affects only ants, including harvester ants and other ant species that compete with fire ants. Since it has the same corn grit and soybean oil base as Amdro, it is attractive to pets and rodents [2], but must be consumed in greater amounts to be fatal, due to its lower toxicity. Logic is also toxic to fish.
Environmental accumulation. Amdro does not accumulate in the environment and is not systemic in plants [8:123]. Logic dissipates rapidly in soil. No residues can be detected three days after application (10:3). Neither product remains toxic for an extended period of time in the environment.
Effectiveness of Amdro and Logic. The initial effects of Amdro are noticeable 1 to 2 weeks after application and theproduct reaches maximum effectiveness in 1 to 1-1/2 months [2]. In a study conducted by Texas Department of Agriculture (TDA) personnel [9:2-3], 8 weeks after a single broadcast application of Amdro on 4 test plots, the number of fire ants and colonies had been reduced by 88% and the toal ant population by 92%. After 35 weeks, 86% fewer colonies existed, compared to pretreatment levels. Ant population had been reduced by 98%. One year and 13 days after the Amdro application, the number of mounds on the test plots ranged from 47% fewer than pretreatment level to 32% more than that level. Population reduction averaged 35%.
Initial effects of Logic are not apparent until 2 to 3 months after application [2]. In the TDA study (9:2-3), 50% of the fire ant colonies had been eradicated and the ant population had been reduced by 92% at 8 weeks after a broadcast treatment of Logic. At 35 weeks, Logic-treated plots averaged an 81% reduction in the number of fire ant colonies and a 98% reduction in fire ant population. One year and 13 days after the application of Logic, levels of mound reduction ranged from 91% to 46%, depending on the plot. Ant population reduction was 87%. Figure 1 is a summary of the results of the study.
8 Weeks 35 Weeks 1 Year, 13 Days
Pop. Mound Pop. Mound Pop. Mound
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Amdro 88% 92% 86% 98% 47-32% 35%
Logic 50% 92% 81% 98% 91-46% 87%
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Figure 1. Table of fire ant mound and population reduction
rates for a single application of Amdro and Logic.Early spring application (as soon as soil temperatures reach acceptable levels) of Amdro would bring fire ant population levels into the range desirable for recreational use of the 10 acre property in 8 weeks or less. An additional fall application of Amdro would be required to maintain acceptable fire ant population levels. Early spring application of Logic would bring fire ant population levels under control in 8 weeks. A single annual application in early Spring would maintain desirable fire ant population levels.
Cost. Both Amdro and Logic have a com grit and soybean oil base [7] and must be used within three months after opening to be effective [1]. Baits are available in large 25 pound and 50 pound quantities for a low price per pound but, for the purposes of this study, large purchases are not cost effective due to the short life of the open product. For the purpose of treatment of the 10-acre property, purchases of quantities of 15 pounds or less are appropriate. Therefore, this cost survey is limited to retail prices of small quantities. Only the lowest prices are reported, excluding taxes. A 1-pound container of Amdro costs $7.99 at HEB grocery stores. At application rates of 1 pound per acre, broadcast twice a year, the cost is $159.80 per year. At application rates of 1-1/2 pounds per acre, the annual cost is $239.70. B&G Company sells 4-pound bags of Logic for $28.79. At application rates of 1 pound per acre, the annual cost of Logic is $86.37. At rates of 1-1/2 pounds per acre, the annual cost is $115.16.
Product costs for Logic are significantly lower than costs for Amdro. Additionally, only one annual application of Logic is required, compared to two aplications of Amdro, so labor costs for Logic are half those of Amdro.
AMDRO LOGIC
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Application rates 1 - 1.5 1 - 1.5
in pounds/acre
Lethal dosage of 1131 9220
active ingredient
in mg per kg
Initial effects 1 to 2 weeks 2 to 3 months
Duration of effects 35 weeks 1 year
at desirable levels
Number of annual 2 times 1 times
applications
Annual product $159.80-$239.70 $86.37- 115.16
costs
Figure 2. Factual Summary of Comparisons of Amdro and Logic.