The Use of Mirex in Control of the Imported Fire Ant

The chemical, physical, and toxicological properties of the chlorocarbon pesticide mirex (C₁₀Cl₁₂), the imported fire ant (Solenopsis richteri Forel and Solenopsis Invicta Buren) which it controls, and the programs designed to effect this control are described. The systematic name of mirex is dodecachloropentacyclo [5.3.0².⁶.0³.⁹.0⁴.⁸] decane. The nomenclature utilized in Chemical Abstracts is dodecachloropentacyclo-1,3,4-metheno-2H-cyclobuta (cd)pentalene. Several arguments emerge both for and against continued use of mirex in the control of the imported fire ant. Those in favor include (i) the fire ant is a major nuisance to those employed in agriculture in infested areas; (ii) a greater risk of allergic response because of increased sensitivity of people in infested areas; (iii) the fire ant does prey on other insects; (iv) reports of toxicity to other organisms are largely laboratory studies; (v) the alternative chemicals, heptachlor and dieldrin, would also present serious problems to the environment; and (vi) the probable wide use of Dechlorane (mirex) as a fire retardant in polymers could easily introduce far more of the chemical into the enviornment than that from pesticide applications. Arguments against continued use of mirex include (i) reports of tumor induction and toxicity in nontarget organisms such as estuarine organisms; (ii) it is not certain that the imported fire ant is a significant economic pest; (e.g., attacks on farm animals are extremely rare); and (iii) long-term persistence of mirex in the environment. The employment of mirex on large areas of territory is a major point of discussion. The alternatives would be intensive hand treatment of mounds, or complete prohibition of the use of mirex for this purpose. Extensive research and monitoring programs are now being conducted in various southeastern USA states with support of the USDA. The Fire Ant Control Program for 1971 included treatment of 1.8 million hectares of open areas but did not include land near lakes and streams. One-seventh of this area was treated with bait that delivered only one-fourth as much toxicant as the previous application. These programs pinpoint the areas of infestation and confine treatment to infested areas where people earn their livelihood. At present, mirex is the best alternative for control of the imported fire ant and aerial application of bait is the only realistic method for effective control. Use should be limited to seriously infested areas and research into possible side effects should be continued and expanded.