FIRE ANTS

 

The red imported fire ant (Solenopsis invicta) is a native of South America that was accidently introduced into the southern United States around 1940. Over the past 50 years, this insect has spread throughout much of the southern and southeastern United States (see distribution map). As populations continue to spread northward, the ants are becoming a common problem for commercial blueberry growers in the southeastern counties of North Carolina. The ants are relatively small (3-6 mm in length) and red to reddish brown in color. They nest in sandy soils and often build large interconnecting colonies with multiple queens. Survival is best in mild temperate climates where winter temperatures rarely fall below 10°F and rainfall exceeds 25 cm (10 inches) per year.

Fire ants are named for their painful sting. Workers are quite aggressive; they stage swarming attacks when their nest is disturbed. The venom from multiple stings may cause nausea, dizziness, and even death.

Illustrations:

  • Nest site of red imported fire ant.
  • Map of distribution in U.S.
  • Workers feeding on ripe fruit.

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    Life Cycle and Seasonal Distribution


    Fire ant colonies are active throughout the year. Cold winter temperatures slow development and drive the ants deeper into the soil, but activity resumes when the temperature rises. Under optimal conditions, development from egg to adult takes less than a month. A single queen may live for several years and produce over five million workers in her lifetime.

     

    Symptoms and Damage


    Although fire ants may feed on ripe fruit, they have only an insignificant impact on crop yields (Payne et al. 1988). In fact, they may even increase the amount of marketable fruit because they are natural enemies of other pests (e.g. cutworms, leafrollers, maggots, etc.) that live or pupate in the soil. Fire ants are regarded as pests primarily because they attack pickers and other agricultural workers who tend the bushes. Accidently stepping in a fire ant mound may quickly become a very painful experience.

     

    Natural Enemies


    In their South American homeland, fire ants are attacked by a surprisingly wide variety of predators and pathogens. But despite ongoing efforts, most attempts to establish these natural enemies in the United States have not been successful (Jouvenaz et al. 1981). Prolonged periods of sub-freezing temperatures and repeated freeze/thaw cycles during winter are probably the most effective ecological control for fire ants in North Carolina.

     

    Scouting, Management, and Control


    There are several formulations of insecticides and growth regulators that are sold for controlling fire ants, but only carbaryl (Sevin) and diazinon are labelled for use in blueberry fields. Sevin can be applied as a foliar spray one day before harvest to kill foraging workers. This provides only short-term protection so pickers can harvest the fruit without being stung. For more long-lasting protection, diazinon is used as a mound drench to saturate the soil and kill the occupants of an entire nest site. Mix one pint of diazinon in 100 gallons of water and use one gallon of this solution for mound up to 8 inches in diameter and two gallons for larger mounds (Banks 1990). Drench treatments are most effective when applied on cool, sunny mornings while the ants, including queens and immatures, are concentrated near the soil surface. Later in the day and during hot, dry weather, the ants retreat deep into the mound where the insecticide is less likely to reach them.

    References

  • Banks, W. A. 1990. Chemical control of the imported fire ants. In: R. K. Vander Meer, K. Jaffe, and A. Cedeno, (eds.). Applied myrmecology, a world perspective. Westview Press, Boulder, CO. pp. 596-603.
  • Jouvenaz, D. P., C. S. Lofgren, and W. A. Banks. 1981. Biological control of imported fire ants: a review of current knowledge. Bull. Entomol. Soc. Amer. 27: 203-208.
  • Payne, J. A., D. L. Horton, and A. A. Amis. 1988. Entomology of rabbiteye blueberries, Vaccinium ashei Reade, in southeastern United States. In: M. K. Harris and C. E. Rogers (eds.), Entomology of Indigenous and Naturalized Systems in Agriculture, Westview Press, Boulder, Colorado. pp. 99-124.

    • Last updated: 2 June 1997
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