The rain and cooler temperatures last week were a blessing. Everything greened up, and the air was fresher.
But some pests came out after the rain.
Last Sunday, I walked out in my yard after the first little shower, and fire ants were making a mound. Fire ants have been pests in this area for a long time, but they can be controlled.
The fire ants that cause us problems were introduced into the United States from South America at the port of Mobile, Ala. The black fire ant, Solenopsis richteri Forel , arrived sometime around 1918, and the red fire ant, Solenopsis invicta Buren , in the late 1930s. Both species probably came to the port in soil used as ballast in cargo ships.
Since its introduction, the red fire ant, a much more aggressive species than the black, has spread throughout the southeastern United States, replacing many native species and displacing the black fire ant.
Beginning soon after World War II, and in conjunction with the housing boom of the period, the fire ant started its march across the South. The spread of these ants was largely due to the movement of grass sod and woody ornamental plants used in landscaping.
One of the identifying characteristics of a fire ant colony is the earthen nest or mound. The mound is a conically-shaped dome of excavated soil that has a hard, rain-resistant crust. Fire ant mounds can be a few inches to 2 feet in diameter and height. Tunnels below the surface radiate from the mound, allowing foraging workers to enter and leave the mound.
Given a dark, protected site with sufficient moisture and an adequate supply of food, fire ants will nest in a variety of sites, such as rotten logs, walls of buildings, under sidewalks and roads, and even in automobiles.
Colonies of fire ants consist of eggs, brood, workers, winged males, winged females and one or more reproductive queens. Among the sterile workers, labor is divided by age. Younger workers are assigned the job of caring for the developing brood; middle-age workers are tasked with colony maintenance and protection; and the eldest workers forage for food.
Alate, or winged forms, are most abundant in the late spring and early summer but can be found at any time of the year.
The winged forms are reproductives. Males are decidedly smaller, glossy black and have a small head. Although both alate males and females can be found in the same colony, as a general rule one form will be dominant. The males fly first and await the females in the air. The female alates emerge and take flight, climbing up into the cloud of waiting males and mating in the air.
After mating, the male dies and the newly mated female lands, sheds her now-useless wings and begins searching for a suitable nesting site.
While attempts to control fire ants over large areas are impractical, there are two basic methods that can successfully control them within a limited area: treatment of individual mounds and broadcast treatments.
Mound drenches with common insecticides are generally effective against fire ant colonies. The mound is flooded with a large volume of a liquid containing a contact insecticide such as carbaryl, acephate or bifenthrin.
A major problem with this method is that the queen is sometimes too deep within the colony to be contacted by the insecticide.
Care must be taken not to disturb the mound before application of the drench. A disturbance will alert the colony and the queen might be taken deeper into the mound. Application of insecticidal surface dusts or granules have a limited effect on a colony if they are not watered in.
Broadcast treatments work well. There are two types of products used for fire ants. One is a contact treatment, and the other is bait. Contact products need to be watered in for best results, while baits need a period of dry weather so they can be taken in as food. Most bait products should be applied in the spring and fall.
Some of the contact products that work are bifenthrin and fipronil. Amdro and Spectricides Once N Done are examples of baits.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at firstname.lastname@example.org.
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