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Plantwise Technical Factsheet

red imported fire ant (Solenopsis invicta)

Host plants / species affected
Abelmoschus esculentus (okra)
Arachis hypogaea (groundnut)
Brassica oleracea var. capitata (cabbage)
Carya illinoinensis (pecan)
Citrullus lanatus (watermelon)
Citrus
Cucumis sativus (cucumber)
Cynodon dactylon (Bermuda grass)
Fragaria ananassa (strawberry)
Glycine max (soyabean)
Helianthus annuus (sunflower)
Ipomoea batatas (sweet potato)
Medicago falcata (yellow alfalfa)
Pinus (pines)
Solanum (nightshade)
Solanum melongena (aubergine)
Sorghum bicolor (sorghum)
Stenotaphrum secundatum (buffalo grass)
Trifolium (clovers)
Zea mays (maize)
List of symptoms/signs
Fruit  -  external feeding
Fruit  -  internal feeding
General Signs  -  Swelling skin or subcutaneous, mass, lump, nodule
Leaves  -  wilting
Ophthalmology Signs  -  Chemosis, conjunctival, scleral edema, swelling
Ophthalmology Signs  -  Conjunctival, scleral, injection, abnormal vasculature
Ophthalmology Signs  -  Conjunctival, scleral, laceration, cut, tear, injury
Ophthalmology Signs  -  Conjunctival, scleral, papules
Ophthalmology Signs  -  Conjunctival, scleral, redness
Ophthalmology Signs  -  Corneal edema, opacity
Ophthalmology Signs  -  Corneal injury, cut, tear
Ophthalmology Signs  -  Corneal neovascularization, pannus
Ophthalmology Signs  -  Corneal ulcer, erosion
Ophthalmology Signs  -  Lacrimation, tearing, serous ocular discharge, watery eyes
Pain/Discomfort Signs  -  Skin pain
Roots  -  external feeding
Roots  -  internal feeding
Seeds  -  external feeding
Seeds  -  internal feeding
Skin/Integumentary Signs  -  Parasite visible, skin, hair, feathers
Skin/Integumentary Signs  -  Skin edema
Skin/Integumentary Signs  -  Skin erythema, inflammation, redness
Skin/Integumentary Signs  -  Skin papules
Skin/Integumentary Signs  -  Skin plaque
Skin/Integumentary Signs  -  Skin pustules
Skin/Integumentary Signs  -  Skin wheal, welt
Vegetative organs  -  external feeding
Vegetative organs  -  internal feeding
Whole plant  -  cut at stem base
Whole plant  -  external feeding
Whole plant  -  internal feeding
Whole plant  -  plant dead; dieback
Symptoms

S. invicta tunnels through roots and tubers, feeds on plants, fruit and seeds and can girdle young citrus trees (Stewart and Vinson, 1991). As well as causing direct damage to plants, S. invicta also aggravates populations of other insect plant pests such as Homoptera (e.g. aphids, scale insects and mealybugs). The ants consume the sugary honeydew produced by these pests and protects them from natural enemies.

Worker ants bite (with mandibles) and sting (with stingers) aggressively and repeatedly. The sting feels like being burned. A day or so later, S. invicta venom forms a white fluid-filled pustule or blister at the red sting site, a symptom characteristic only of fire ants.

Prevention and control

Efforts to eradicate spot infestations of this species (e.g. in Brisbane, Australia, and parts of California, USA) are ongoing. In southeastern USA, eradication efforts have been abandoned and integrated pest management approaches have been developed to eliminate problems caused by this species where and when they occur.

Phytosanitary Measures

The inspection and treatment or elimination of the soil comprises phytosanitary methods that are designed to prevent or mitigate the further spread of S. invicta.

Cultural Control and Sanitary Methods

Some cultural management approaches in cattle production systems, such as the use of disc-type cutters, the quick removal of hay bales from the field and the scheduling of cow fertility programmes to avoid calving during hot, dry summer months have been promoted. Some landscape elements have been evaluated that are believed to repel or be less attractive to these ants.

Biological Control

A thorough review of the biological control of S. invicta can be found in Williams et al. (2003). Current efforts are focusing on the use of several species of parasitic flies (Diptera: Phoridae). Pseudacteon tricuspis, P. curvatus, P. litoralis, P. obstusus and P. cultellatus have been introduced and have established in the USA (Graham et al., 2003).

Other species are currently being studied as candidates for future releases. The microsporidium Kneallhazia solenopsae (synonym: Thelohania solenopsae) has been detected in southeastern USA and has been used to inoculate healthy colonies in the field and laboratory. Another microsporidium, Vairimorpha invictae, has been studied in Argentina (Briano and Williams, 2002; Valles and Briano, 2004; Briano, 2005; Birano et al., 2006) and the USA (Oi et al., 2005)

Many other natural enemies of S. invicta and related fire ant species have been identified and studied. Few are candidates for classical or importation biological control programmes because they do not spread between colonies in the field and do not sustain themselves in the environment. Native and exotic competitor ants, which prey on newly mated fire ant queens, raid or disrupt small colonies and/or compete for nesting sites and resources, are considered important biological resistance factors. They could help prevent high population levels of S. invicta and should benefit from the establishment of classical biological control agents that will reduce the exotic species' capacity to out-compete these species (Porter, 1998).

Chemical Control

Collins (1992), Williams et al. (2001) and Drees and Gold (2003) provided reviews of the history of control developments, efforts and strategies. Chemical control options include broadcast application of bait-formulated insecticide products, the treatment of individual ant colonies in mounds and surface or barrier treatments using contact insecticides. Regardless of method used, the objective is to kill not only the workers but also the queen, because she is the only ant capable of laying eggs. Common insecticides that can be used for fire ant control were given in Greenberg and Kabashima (2013).

IPM

Drees and Gold (2003) presented an account of the development of integrated pest management (IPM) approaches or programmes to suppress S. invicta population levels where they are needed or justified. Quarantine treatments of nursery stock and other regulated items are detailed in a publication by the USDA Animal and Plant Health Inspection Service (Anon, 1999a).

Impact

Although the exact economic costs of fire ant damage and control are unknown, estimates for southeastern USA have been more than half a billion to several billion dollars per year (Williams et al., 2001). The costs associated with S. invicta accross all the USA have been estimated at US $1 billion per year. In 1998, the average household cost for imported fire ant problems per Texas household in urban areas was US $150.79, with US $9.40 spent on medical care. The total annual metroplex (Austin, Dallas, Ft. Worth, Houston and San Antonio) expenditures for medical care costs was 9% or US $47.1 million of the US $526 million total expenditure cost due to S. invicta (Lard et al., 2002).

The Australian Bureau of Agriculture Resources Economics has estimated that losses procured in rural industries to have amounted to more than AU$ 6.7 billion over 30 years (ISSG, 2014). In the case of introduction and establishment of S. invicta in Hawaii, researchers have estimated the impact on various economic sectors would be around US $211 million per year (Gutrich et al., 2007).

Equipment Damage

S .invicta may infest electrical equipment (such as computers, swimming pool pumps, cars or washing machines), thereby becoming a nuisance or even a danger to people. The ants or entire colonies move into buildings or vehicles seeking favourable nesting sites, particularly during flooding and very hot, dry conditions. Fire ant foraging and nesting activities can result in the failure of many types of mechanical (such as hay harvesting machinery and sprinkler systems) and electrical equipment (including air conditioner units and traffic box switching mechanisms).

Agricultural and Ecological Impact

In addition to being considered medically important pests of people, pets, livestock and wildlife, imported fire ants can also damage crops such as corn, sorghum, okra, potatoes and sunflowers by feeding on the seeds, seedlings and developing fruit. Teal et al. (1999) documented the impact to cattle production systems. The predatory activities of fire ants suppress populations of ticks, chiggers, caterpillars and other insects. This predatory activity reduces the wildlife in some areas.

Seed is generally unaffected by S. invicta in storage. However, once planted, the seeds of many plant species become vulnerable to S. invicta predation and the foraging worker ants consume all or parts of the seed and/or move the seed to new locations. Drees et al. (1991) investigated the factors affecting sorghum and maize seed predation by foraging S. invicta

These stinging ants also affect many animals, particularly those that can not quickly move away from the threat (e.g. very young, old or confined animals). The ants move to moist areas of the body (eyes, genitals), the yolk of hatching birds and wounds, and begin stinging when disturbed. The stings result in injury such as blindness, swelling or death. Indirectly, the animals avoid infested food, water and nesting areas. The ants can reduce the food sources for some insect-eating (insectivorous) animals such as some birds and lizards, and they may compete with seed-feeding (gramnivorous) animals for food or alter the distribution and composition of plant communities.

In addition to direct damage to plants, S. invicta also aggravates populations of other insect plant pests such as Homoptera (e.g. aphids, scale insects and mealybugs). The ants consume the sugary honeydew produced by these pests and protect them from natural enemies. However, the ants primarily prey on arthropods such as some species of ticks, many caterpillars and others often considered pests. This behaviour can provide benefits to producers of cotton, sugarcane and other commodities.

Related treatment support
 
External factsheets
University of California IPM Pest Management Guidelines, University of California, 2009, English language
University of California IPM Pest Management Guidelines, University of California, 2009, English language
University of California IPM Pest Management Guidelines, University of California, 2010, English language
University of California IPM Pest Management Guidelines, University of California, 2009, English language
NCAT ATTRA Pest Management Publications, The National Center for Appropriate Technology (NCAT), 2003, English language
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