Resistance Management Reviews

Fire Ant Behavior - A Guide for Control
By Dr. Terry Mabbett

Research at Imperial College, University of London is helping to tame one of North America's most feared and loathsome public health pests. Red imported fire ant (IFA) (Solenopsis invicta Buren), introduced from South America 70 years ago and currently infesting 250-300 million acres in eleven southern states are fierce, territorial, and persistent. Each fire ant nest may contain up to 3000 'queens' that offer enormous reproductive potential. Throughout spring and summer, active mounds send out 'swarmer' ants (wingless males and females) that start new colonies. These are established in a wide variety of environments including picnic area, playgrounds, pool areas, and around buildings at home and at work. Fire ants deliver a nasty sting - capable of killing hypersensitive people - and as such are a priority target for North American pest control operators (PCOs).

The red IFA also disrupts a wide range of agricultural operations. Reports of attacks on livestock including piglets, new-born calves, and chicks are widespread as is crop damage from ants gnawing holes in roots, stems and buds of a wide range of crops. Red IFA mounds disrupt crop harvesting leaving farmers with two unsatisfactory options: to push the mounds over with plowing equipment, reducing yield and risking equipment damage, or to avoid the mounds, reducing the area of the harvested crop.

Control by insecticide baiting of mounds relies on worker ants bringing back active material into the nest to ensure that the queen(s) die. Many factors including heavy rain, poor bait placement, and bait shyness may conspire to cause control failure. Gordon Daly (postgraduate student on the MSc Pest Management Course at Imperial College, Silwood Park, England) looked at red imported fire ants management from an altogether different angle. Using four different synthetic pyrethroid insecticides - lambda cyhalothrin, deltamethrin, bifenthrin, and betacyfluthrin - he evaluated the magnitude and consequences of perceived fire ant repulsion and activated behaviorial responses following contact with these insecticides.

Fire ants react with a 'hot coals' response, which involves the ants walking up to the deposit of insecticide and promptly retiring. Research is underway to determine the nature of this behavior and to evaluate whether positive results, such as keeping fire ants away from buildings, are outweighed by potentially negative effects. It is suspected that a reduced exposure time of worker ants to insecticide deposit means they will fail to pick up a lethal dose of insecticide and carry it back to the nest. To examine the pesticide exposure of ants within the colony, Daly looked at the role of other ants in the nest. The necrophytic/necrophagic ants remove those that have died of insecticide poisoning and place them outside the nest. If insecticide is intended to reach ants resident in the nest, including nurse ants, larvae, and queens, it is crucial for the insecticide deposit to be acquired from the cadavers and passed up the 'chain of command' to the queen.

The sequence of events, observed and recorded by Gordon Daly, which describe the response of red IFA workers to residual deposits to synthetic pyrethroid insecticides are as followes: