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(BASIC) Managing Fire Ants


Kern County BASIC Pilot Program

Everett Dietrick to Growers September 4, 2001

Managing Fire Ants for Ecologically Based Pest Management (EBPM)

Fire ants have been observed on all five of our cooperator cotton farms, which cause significant, persistent interference with biological control. The significance of this interference to our goal of pesticide use reduction has led me to find the latest research on the biology of the fire ants we are dealing with. We must manage them in order to restore the biodiversity that supports biological control. As explained below, it is possible that if the fire ants are managed, farmers of all crops in Kern County may be able to reduce or eliminate late season pesticide applications for aphids.

The Southern Fire Ant (SFA) is the native fire ant species that has always been present in Kern County. Its natural range used to cover the southern half of the United States as far north as San Francisco, all of Arizona, New Mexico, Texas. Oklahoma, Arkansas, the southern half of Tennessee, and dipping south to all of South Carolina but not North Carolina on the east coast.

The main natural enemies of this ant are other indigenous ant species through competition for food. There were few complaints and little information published about SFA before the more aggressive exotic imported fire ants invaded the southern United States. During the past six or seven decades there has been an invasion of exotic imported fire ants (IFA). This former range has come to be dominated by the IFA, which displaces SFA where or whenever they come into contact.

A report “Red Imported Fire Ants:

Impact on Biodiversity” about the biology of RIFA was recently published by Wojcik, D. P. et al (Spring, 2001). Researchers state that imported fire ants feed on a wide variety of insects and mites. They have received some attention as general predators and scavengers, but many researchers now agree that imported fire ants attack, kill and consume any invertebrate that does not defend itself adequately or escape. Background about imported fire ants and the government eradication program is provided in a footnote.

In spite of the millions of dollars that were spent on chemical pesticides, the RIFA has continued to spread across the south from the eastern states throughout East Texas with newly infested areas in West Texas, New Mexico, Arizona and Los Angeles and Orange counties of California. RIFA has displaced SFA throughout more than half of the original range of the native SFA. It continues to expand, with new infestations in almond orchards in Kern County, in ornamentals in Las Vegas, Nevada, infestations in over 16,000 acres of Orange County, and in desert irrigated agriculture in Coachella Valley in Riverside County––invading 60 new counties across the United States. The status of RIFA in Mexico is not reported on. It is worthy of note that this expansion of RIFA has taken place in conjunction with a world–wide massive growth in conventional chemical control (particularly herbicide use) as well as the chemicals used for the RIFA eradication campaign throughout all of these states.

Fire ants, like another notorious ant import, the Argentine ant, Linepithema humile, which possibly came from the same area of South America, are known to tend whitefly, aphids, mealybugs and other honeydew–producing insects. Ant interference research has documented that it is impossible to farm and garden successfully without management of the excessive populations Argentine ants. When these two imports meet, the Argentine ant often replaces most native fire ants, except the RIFA. Replacing one pest for another is hardly a solution.

The expansion of the fire ants has greater ecological effects than has been documented. It may be that the successful spread of the RIFA and the increased interference to biological control by native fire ants, SFA, in California are both, at least partly, caused by growing dependence on conventional chemical farming, in particular greatly increased reliance on herbicides. Pesticides (particularly herbicides) create more open exposed weed–free spaces throughout the plantscape that are favorable for fire ant nest establishment. This is particularly the case for adjacent interfaces between field roads, irrigation ditches and tail–water drainage areas located between the main crops.

There is estimated to be only one successful nest establishment per one thousand mated female attempts to make new colonies that result from nuptial flights among RIFA. Suppose that an increase in favorable open, exposed space for fire ant nest building has increased the success rate for establishing new colonies in the agricultural plantscape increases several fold by chemical farming processes that favor successful fire ant nesting site availability. The overwhelming desire to eradicate weeds using the chemical hoe saves labor costs, but when used routinely to kill the last weed, this practice expands the habitat for all ants, the native SFA and the imported ones. Such a change in conventional farming practice has accompanied the RIFA eradication effort, by increasing the spread of new colonies. Expanding the distribution of ant colonies in the plantscape increases exposure of ants to pesticides and the selection of resistance among insects and weeds.

We are seeing evidence of negative ecological effects by SFA in alfalfa hay production near our cotton fields. SFA has expanded into alfalfa fields occupying nesting sites on the raised borders within the fields as well as the borders mentioned above. They appear where they escape flood irrigation and cultivation that harm nests. The areas associated with nests develop hotspots of pests (aphids, whitefly, worms and many other potential pests of vegetable and field crops). When alfalfa hay is mowed, more pests migrate from the alfalfa hay into adjacent crops. When the alfalfa hay is treated with pesticides, the damage to natural enemies becomes the problem. Pests of alfalfa present when it is mowed and harvested are forced to seek food and shelter in neighboring fields. Increased pesticide use ultimately increases selection of resistance, which increases pesticide use. Even worse, the alfalfa hay no longer acts as a trap crop providing biological control into adjacent market crops. Unsprayed alfalfa has always been an asset, which exports mostly the beneficial insects during hay harvest (documented research of the 1950s).

The increase in number and distribution of fire ant colonies in recent decades would account for the increased interference to biodiversity and to natural enemies, thus, causing more potential minor pest situations to become major problems needing pesticide suppression. This could especially be the case whenever chemical weed control dominates the plantscape. Round–Up ready crops are another quick fix, the long–term ecological effects of which are debatable. More sustainable farming processes are available.

Flood irrigation interferes with ant foraging and floods out their nests. Permanent nests are distributed around the edges of flood–irrigated fields. Cultivation practices will disturb many new nests created by nuptial flights of sexuals so long as they can be programmed. Sprinkle and drip irrigation, however, favor increasing widespread distribution of fire ants since we have reduced the impact of cultivation that disturbs new nests. New nests can escape cultivation interference where successful nest formation is located very close to the plant trunk, and the mated female (new queen) will reside among the roots near the crown between the furrows, disturbed only by the soil that covers the crown around the young plants. When foraging for food, cultural farming activity can set SFA colonies back. However, many of the new queens will escape flood irrigation and cultivation especially as honeydew and the insects that produce it become more plentiful.

The new fire ant colonies that become established early in the plant growth cycle have difficulty maintaining enough workers to harvest food for the queen, protect and tend her and the eggs and young, and still increase the population within the colony. When the cotton plants become too large for cultivation, the fire ants are free from that cultivation damage. With less disruption of the nest and the colony, they are able to forage more food. The foragers begin tending the honeydew–producing insects for their bounty of liquid that is easy to transport and digest. More plant material supports more insects, few of which can defend themselves or escape from foraging fire ants.

This explains how populations of cotton aphids, whitefly and indirectly all of the potential pests in the field increase when cultivation ceases. Colonies of aphids and whitefly lay a pheromone trail signaling for the trailing worker ants to exit from the nest. This cast specializes in protecting the insects that provide honeydew and in traveling to and from the honeydew source harvesting liquid food that all members of the colony can digest. This increased foraging efficiently speeds up food collection that in turn results in more eggs being laid and expansion of the colony. All the while, the foraging ants are beating off all the predators and parasites that would normally be keeping aphids, whitefly and other pests under good biological control.

This problem of ant interference to biological control is encountered to some extent in nearly all crops from almonds to zucchini squash. With RIFA it is reported to be worse due to multiple queen colonies. Fire ant queens can live several years when the colony is strong not disrupted. If a queen is lost, the colony can support itself by cannibalizing the brood until a new queen is grown. The whole fire ant colony adjusts its size to survive the hardships caused by ant natural biological controls, irrigation, cultivation, pesticide applications and climate.

SFA have natural enemies. They are first of all vulnerable to other ants, which can at least keep the colony busy defending itself from nest raids of other ants. When they are defending the nest they cannot fight the biological controls of aphids and whitefly for access to the honeydew source. There is a long list of insects and other organisms that destroy fire ants in natural ecosystems. They have not been as carefully studied for SFA in the agricultural ecosystem. Most reports are about RIFA are in the eradication zones. There are reports of their predation on boll weevil, sugarcane borers and others where they ultimately destroy biodiversity and become the only surviving but very effective predator. This high–density attack is spectacular but is no substitute for a diversity of natural enemies that manage pests at low densities. Far less is said about their interference to successful biological control processes.

SFA in our fields have Phorid flies that parasitize ants, which we find in our D–Vac samples. Tiger beetles are encountered at the edge of cotton fields. Ant lions battle the fire ants in sandy loam soils. Spiders, lizards, birds and small mammals feed on insects and undoubtedly some will eat ants. Also hot daytime temperatures are a deterrent as ants seek the protection of the cool climate within the nest and abandon their efforts at protecting whitefly and aphids during these intervals. Parasitic wasps have an opportunity to lay their eggs in their hosts when the ants retire to the nests. This is evident in the cotton aphid more than the whitefly, since we have not recovered any of the known parasites of whitefly in any of our experimental fields.

Probably, ant management can be best accomplished by concentrating at the observable nesting areas along the field roads and outside edges of the fields. The cemented irrigation ditches where water is available most of the time are attractive nesting sites. Drip irrigation systems favor fire ant colonization. This is particularly evident in grapes where mealybugs are associated with ants along driplines. All open bare ground space surrounding the field should be monitored. Maintain an on–going campaign by the irrigation crew to disturb nests with a spade or shovel (a machete also works well). This has been shown to decrease foraging long enough to allow natural enemies the opportunity to attack their prey. It forces the workers to return to the nest to repair the damage and protect the queen at all cost. This allows the biological control forces to suppress the pests and surge ahead of the ants in the battle of the bugs.

In this battle of the bugs many beneficials are killed or driven away by ants from the whitefly or cotton aphid. Moreover, predators and parasites that foraging fire ants encounter in search of their prey end up as solid food for the colony. As hotspot of pests protected by fire ants increases, they provide even more honeydew to support ant expansion and attracts more solid food to the hotspot as well. This increase in insect density is most observable around the outside edges of the field or wherever permanent fire ant nesting is taking place. The SFA colony works like a single organism. Loss of a queen can create problems for the colony. Physical disturbance affects workers, sexuals, nurse ants tending each egg, young larvae and old larvae (the only caste that can digest solid food). Nest disturbance can interfere with all of their foraging and food–harvesting activities until reorganization can occur. Thus, the ant colony decreases in size during hardship and increases when foraging is bountiful.

Physical disturbance can be combined with a drench or injection of registered pesticides. Or there are poisoned baits that may be placed near the nests. These baits are taken by the foraging ant workers and fed to the queen and the brood. Over a few weeks the poisons accumulate in the queen and the brood and will destroy the colony. Ready to use (RTU) baits developed for the RIFA attract the foraging workers if applied close by the nests. Liquid bait is carried like the honeydew to the nest where it is regurgitated to feed the queen and the brood and nest mates. The foragers have a broad and opportunistic diet. In other words they may eat anything and seek foods higher in proteins than carbohydrates (e.g. honeydew). They prefer the germ of seeds that have high protein and fat. Research in New Mexico revealed that seeds stored in the nest by SFA supplied 25% of the diet. A combination of freeze–dried egg and anchovy were identified as the best baits for use with poisons. Nest mates practice a begging process that insures that all receive sufficient food. The hungry ones get food from the full individuals until all are equally fed.

However, the common ant foods in cotton are other insects, predators and parasites and some pest insects and honeydew carried to the nest by group foraging. The long lines of workers extending from the aphid and whitefly sources to the ant nest form an efficient method to exploit hot spots of pests to feed more and more ants. All life stages can eat liquids but only the large mature larvae are capable of digesting solid food. The foragers have a filter that screens out particles as small as bacteria O.02 microns. These solids are formed into pellets that are carried in a separate pouch to be fed to the more mature larvae that lack such solid food filters. Liquid baits might affect some castes sooner than granular forms.

When transitioning to reduce pesticide use on the farm, a practical approach is to identify through monitoring procedures the progress of observable biological control processes among the potential pest and beneficial populations. When a pest situation is seen to begin developing, look for ant interference and begin a campaign of physical disruption that may be combined with pesticide drenches or poisoned baits. It is far easier to suppress ants and restore and augment biological control than to trigger the pesticide treadmill with conventional chemical control of the whole field.


Imported fire ants (IFA) were first reported as a pest complaint in 1918. There may have been several importations of fire ants but ant experts now agree that the Black Imported Fire Ant (BIFA) entered in 1918 and the Red Imported Fire Ant (RIFA) entered between 1933 and 1945. The early reports are confusing in that the taxonomists had not decided to split the species and the referenced names were often lumped into a complex of fire ant varieties. There was the opinion that the black and red were only color variants of the same species and the native species now called SFA was hardly mentioned other than that it fed on honeydew and was reported to be mostly beneficial. The sting was often described as a bite and therefore less toxic than imported fire ants. With the RIFA came the eradication proposal. Funds focused on the massive efforts to eradicate the IFA, in particular the Red Imported Fire Ant (RIFA). The areawide war on this ant began and continues to this day without much success. There was extended research, broad–spectrum chemical war and ultimate failure to eradicate RIFA.

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