Mickey Eubanks

 Red imported fire ants (Solenopsis invicta) are extremely obnoxious pests that virtually every Alabama homeowner would love to see disappear. Most Alabama farmers feel the same way. Large fire ant mounds severely damage farm equipment during soybean and hay harvest, sting farm workers handling harvested cotton and other crops, and attack IPM workers as they scout infested fields.

Fire ants, however, can be beneficial under some circumstances. One of the hidden costs associated with reducing fire ant abundance in crops could be increased damage from insect pests that are currently suppressed by fire ant predation. Fire ants are voracious predators that consume large numbers of insects and other arthropods and are often the most abundant predators of plant-feeding insects in cotton, soybean, peanuts, corn, and other important agricultural crops.

To measure the impact of fire ants on pests as well as beneficial insects and arthropods, AAES researchers sampled cotton fields at the E.V. Smith Research Center and soybean fields owned and operated by independent growers in Talladega County. From early May until late September of 1999, sweep nets were used to collect foraging fire ants and other insects and arthropods from plant foliage. Samples were returned to the laboratory at Auburn University, and insects and arthropods were identified and data were analyzed.

Results from this study suggest that fire ants are important predators of several key pests of Alabama crops; in other words, the more fire ants foraging in the foliage of soybean and cotton plants, the fewer insect pests found, including some of the most serious pests of these crops (Table 1). For example, fire ants were extremely effective at suppressing weevils in cotton and stinkbugs in soybean. Under many conditions, fire ant predation is intense enough to maintain populations of pests below action threshold levels (the point at which a grower must take some action against the pest to avoid economic loss) providing real financial savings to growers.

AAES research also reveals, however, that fire ants attack and consume other beneficial insects and arthropods. Fire ants reduced the densities of 15 important types of beneficial insects and arthropods in at least one of the two crops studied (Table 2). Many of these, including predaceous ladybird beetles, big-eyed bugs, spiders, and wasps, are important biological control agents that frequently suppress populations of insect pests. Any evaluation of the importance of red imported fire ants as economically important predators of insect pests must also include an evaluation of lost pest control as a result of fire ant predation on beneficial insects.

AAES researchers are currently constructing statistical models of the food webs involving red imported fire ants in Alabama agricultural crops. These models allow researchers to compare the direct effects of red imported fire ants on insect pests (predation of pests) and the indirect effects of fire ants on agricultural pests (potential loss of pest control as a result of fire ant predation on other beneficial insects and arthropods). These models indicate that red imported fire ants are important predators that suppress populations of insect pests in agricultural crops, but these models also suggest that the impact of fire ants on other beneficial insects can be far more powerful than their impact on pests.

In the summer of 2000 AAES research will experimentally test these models to ultimately determine if the benefits of fire ants as biological control agents outweigh the negative impact of fire ants on other beneficial insects.