Black fire ant (Solenopsis richteri (Forel)). The less common black imported fire ant arrived mysteriously in the United States in 1918 through the port of Mobile, Alabama, but escaped recognition as a new arrival until 1930 (Summerlin and Green 1977). In South America, its range covers extensive areas in Brazil, Uruguay, and Argentina (Buren et al. 1974). In the United States, its distribution includes only northeastern Mississippi and northwestern Alabama. This limited range is probably due to competition from its relative, Solenopsis invicta Buren.
Solenopsis invicta. This fire ant is well established in most of Florida and from North Carolina to eastern Texas. Much of the early spread was by transportation of infested nursery stock. This species is native to the seasonally flooded Pantanal region of southern Brazil and was introduced by some form of shipping to the United States about 50 years ago (Lofgren 1986). The prediction of the ultimate range of S. invicta is contentious and depends on certain biological assumptions (Tschinkel 1993). There is evidence that it will not spread farther north than the northern boundaries of Mississippi, Alabama, Georgia, and the Carolinas. Colony development and reproduction are probably controlled by the brevity of the winter season and the fact that this species does not hibernate.
These two nonindigenous fire ant species inhabit approximately 93,120,000 ha in nine southern states, making them a familiar feature of life in these areas (Lofgren 1986). In that range are about 10 billion colonies (Metcalf et al. 1982; Davidson and Stone 1989). The ants are feared because, when a nest is disturbed, the ants swarm over any nearby object, delivering multiple, painful stings to the intruder. This aggressiveness extends only to a small area around the nest, which is a conspicuous mound (Sterling 1978). The behavior is, in fact, not unlike that of the well-known winged relatives of the ant -- bees and wasps (Davidson and Stone 1989).
The ant is ubiquitous in agriculture. It has been reported in almost every crop in the infested states; although it causes damage, it is also sometimes beneficial because it preys on a wide variety of insects (Davidson and Stone 1989).
Except for the expanded range, the status of the fire ant is similar to what it was in 1957 when the U.S. Department of Agriculture first attacked fire ants with the largest and most devastating eradication ever undertaken against an introduced insect pest. More than 25 years and close to $200 million later (Oliver et al. 1979), the situation is now worse than ever (Davidson and Stone 1989). The consequences from the introduction of this species for humans are harmful, effects in agriculture are both harmful and beneficial (Lofgren 1986; Tschinkel 1993).
Specific damage and benefits to some of the commonly cited crops were summarized by Davidson and Stone (1989). The most seriously affected crops are soybeans (Soia soja) and hay (bales left in the field overnight attract hordes of ants, and the mounds may obstruct cutting rigs). Fire ants are most beneficial to cotton because they prey on boll weevil (Sterling 1978) and Heliothis species and to sugarcane because they reduce sugarcane-borer populations to allow farmers to save one or two pesticide applications per season (Maxwell et al. 1982; Davidson and Stone 1989). Lofgren (1986) summarizes the economic importance and control of fire ants in the United States.
The general opinion in the literature before 1957 was that fire ants were not significant agricultural pests and may indeed be overall beneficial. The ants are a nuisance in certain settings. Green (1952) pointed out that the most serious damage in agriculture is that the imported fire ant build very large mounds in the fields causing problems during cultivation.. Brown 1982 reported that infestations may have as many as 198-222/ha and in severe cases as many as 1500/ha in Texas. Tschinkel (1982) claimed that the upper limit is 49-62/ha in large, mature colonies. Even in this smaller number, however, the presence of ant mounds can seriously affect agricultural cutting and mowing. Because the ant mounds can reach a height of 30.5 cm and a diameter of 61 cm, damage to farm machinery is inevitable if mounds are scattered throughout a field. Crop costs rise from broken combine blades or from times of equipment repair (Davidson and Stone 1989).
Efficiency of farmworkers is lost if workers must constantly avoid ants. Absences from the workplace for medical treatment and medical expenses introduces additional costs. Some activities, such as removing infested bales of hay and making on-the-spot repairs of machinery near ant mounds, are impossible in the presence of angry fire ants (Davidson and Stone 1989).
Attacks on newborn calves and other livestock have been recorded but are poorly documented. Fire ants reportedly kill quail, ground squirrels, young deer, and even earthworms (Brown 1982; Davidson and Stone 1989).
Several points relate specifically to consideration of eradication. First, fire ants may have already reached the limits of their range in the United States. Cold temperatures stopped their northward spread, and the need for warm rain may prevent their westward movement. Texas west of the hundredth meridian may be too dry, and California, which lacks summer rains, may be too dry in the warmer months (Davidson and Stone 1989).
Second, mature colonies of fire ants are territorial. Within an area around its nest, a colony does not tolerate ants from another colony and kills newly mated queens that attempt to found a nest. As a result, fire ant populations have a self-imposed carrying capacity of approximately 62 mature mounds/ha (Tschinkel 1982). Counts higher than this indicate young colonies in the growth phase (Davidson and Stone 1989).
The feasibility of eradication was broached and answered in the negative only after the situation had been badly mishandled (van den Bosch 1978). If the biology of the ant had been examined, the environmental poisons heptachlor and dieldrin would probably not have been considered. The idea of using a broad-spectrum pesticide on a species that is well adapted to colonizing disturbed areas would have seemed ridiculous (Davidson and Stone 1989).
By steadfastly refusing to succumb, fire ants forced a reexamination of eradication philosophy. But the costs of that lesson have been considerable in dollars and in harm to the environment (Davidson and Stone 1989).
The native ant fauna of the United States includes two fire ants, the tropical fire ant (Solenopsis geminata (F.)) and the southern fire ant (S. xyloni McCook). Both are regarded as inconspicuous members of the southern ant fauna. They make smaller mounds than the imported fire ants and are relatively unaggressive (Summerlin and Green 1977).
Lovebugs (Plecia nearctica). Love bugs, also called marsh flies, belong to the Family (Bibionidae). This species was first described by D. E. Hardy in 1940 in Louisiana, where many larvae developed in grass clippings along highway subgrades. Although Hardy's description of the species did not list any localities east of the Mississippi Gulf Coast, he indicated that the species was widely distributed and extended into Mexico and Central Mexico (Hetrick 1970).
Love bugs are not native to Florida but migrated into Florida from the west. The first reported love bug in Florida was in Escambia County in 1947(Kuitert and Short 1993). The first time they were reported in Alachua-Marion counties was in 1955-1956. They have progressively moved southward each year to Homestead and northward to Georgia and South Carolina. Flights of large numbers of adults are present for 4 weeks each year in May and September. The flight of the love bug is restricted to daylight hours. At night, the bugs rest in low-growing vegetation (Kuitert and Short 1993). Individual insects do not live long but are constantly being replaced by others of the same generation. Male love bugs live for 2 or 3 days, whereas females may live for 1 week or longer and may mate with more than one male (Hetrick 1970).
In September 1971, love bugs were reported as far south as south-central Florida, and scattered flights were seem as far south as the Lake Okeechobee area (Kuitert and Short, 1993). Adult love bugs are harmless and do not sting or bite. They feed on nectar and pollen of various flowers, especially goldenrod, (Solidgo spp.), sweet clover (Melilotus spp.) and Brazilian pepper (Schinus terebinthifolius).
The love bug is a nuisance but not yet an environmental pest. However, its population has increased, and its range has spread in such proportions that some form of ecological imbalance may be expected (Peckham 1977). Love bugs spatter and stick to trucks and automobiles during daylight hours, often clog the cooling fins of the radiator, and may cause automobiles that travel at high speeds for extended time to overheat. Windshields that are covered with these insects obscure the driver's vision, and a cars finish may be damaged if the bugs are not cleaned off in a reasonable time (Kuitert and Short 1993).
At the present time, the chemical control of this species is impractical and environmentally unsound. The larval and adult stages of this species have many enemies, including birds, earwigs, centipedes, and two species of beetles (Kuitert and Short 1993).
The ecological factors that are responsible for the population explosion of this species in north central Florida are not known (Hetrick 1970). Love bugs occur in great numbers along the highways because the photochemical reaction of automobile exhaust fumes and UV radiation attract and hold them over the highway (Callahan and Denmark 1973).
