|Red Imported fire ant: Solenopsis invicta Buren|
|Description and Biology: The
red imported fire ant, known for its painful sting and venom that produces
a unique white pustule, has replaced many native ants in areas it infests.
Red imported fire ant colonies consist of the brood (cream-colored eggs,
larvae, and pupae) and several castes of adults. Adults include winged males
(distinguished from females by smaller heads and black bodies), red to brown
winged females, one or more queens, and workers. Worker ants are wingless,
sterile females, and vary in size. Older workers forage or defend the nest
while younger workers care for the brood.
A newly-mated queen lays a cluster of a dozen or more eggs. When the eggs hatch six to 10 days later, the queen feeds the larvae infertile eggs, regurgitated oil from her crop, or protein secretions from her salivary glands. An older queen can lay 200 eggs each day. Older larvae receive food gathered by worker ants. Larvae develop in six to 10 days, and pupate. Adults emerge nine to 15 days later. The average colony contains 100,000 to 500,000 workers, several hundred winged forms, and one or more queens. Queen ants live for five or more years.
New colonies do not produce a conspicuous mound for several months. Mounds are built in almost any kind of soil, but open, sunny areas such as pastures, meadows, and cultivated fields are preferred. The size of a mound depends on soil characteristics and land disturbance, but mounds can be 25 to 30 cm tall. Mounds are smaller in sandy soil. Mounds often are located in rotting logs, around stumps and trees, and occasionally under buildings.
|Symptoms and Damage: Although considered in some agricultural situations to be beneficial because they consume other insects, red imported fire ants feed on planted sorghum seed. They occasionally damage roots and leaflets of germinating seeds. Worker ants chew through the thin seed coat and remove the embryo (germ). Rarely is the endosperm (starch) of the seed consumed. Water-soaked or germinating seeds are preferred, but dry seeds also are damaged. The embryo and some of the surrounding endosperm are hollowed out, leaving a ragged and pitted hole. This damage results in loss of seed germination causing reduced sorghum plant stands.|
Management: Production practices helpful in reducing the effects of wireworms on planted sorghum seed also reduce damage by red imported fire ants. Rapid seed germination is very important. Amount of damage caused by red imported fire ants to sorghum is influenced by the length of time the seed is vulnerable (dry and germinating) and by the abundance of the ants. In addition to using seed treated with insecticide, seed with good vigor should be planted into a well-prepared seedbed. Soil should be packed firmly, particularly during dry conditions, to cover seeds and make them less accessible. No- and reduced-tillage favor red imported fire ant.