Solenopsis invicta- Tyler Bunting

Taxonomy

Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Hymenoptera

Family: Formicidae

Subfamily: Myrmicinae

Genus: Solenopsis

Species: S. invicta

Description

The Red Imported Fire Ant is arguably the most infamous ant species out of the 280 species that can be found in the genus Solenopsis. This aggressive ant can be located all over the globe and is thought to be expanding its range. Although recent studies have suggested that another invading ant species, Nylanderia fulva, is competing with the Imported Red Fire Ant and limiting its range slightly (Lebrun 2013). These ants are considered pests for a multitude of reasons, the most commonly known being their venomous attacks that can cause severe allergic reactions and result in secondary infections, anaphylactic shock and in extreme cases death (Wetterer 2013). Apart from their painful bite, these ants cause havoc due to their mound building lifestyle which can damage plant roots causing devastating effects on crops.

The general appearance of this is a small reddish brown color with a size that can vary between three to seven millimeters in length. It is often difficult to distinguish between the Red Imported Fire Ant and its close relative the Black Imported Fire Ant, Solenopsis richteri. Often identification between the two species must be made using high performance liquid chromatography which allows researchers to spot differences in cuticular hydrocarbons.

Distribution

While Solenopsis invicta were originally found in regions of South America, today they are an invasive species to many different areas. These Imported Red Fire Ants, as their name suggests, were first accidentally imported to North America within the past century (Ascunce 2011). According to record these ants were first introduced to a port in Mobile, Alabama via ship sometime between 1933 and 1945 (Wetterer 2013). At first these ants could only be found in the Southern states but are now located as far as California. After its introduction to North America Solenopsis invicta rapidly invaded areas around the globe such as, the Caribbean, Australia, New Zealand, Taiwan, Hong Kong, Macao and China (Ascunce 2011).

Solenopsis invicta Venom

A common misconception about ants is that during an attack the ants only bite to inflict injury to their victims. While biting is an integral part of ants attack strategy, the mandibles are not the storage site or delivery method of the painful venom. In many ant species, biting is just a way to break the enemies skin, after which venom is sprayed onto the open wound. Solenopsis invicta differ from this slightly, instead the red imported fire ants use their mandibles to latch on to their victims. They then arch their backs under their abdomen and and force a stinger into the tissue, introducing their venom (Baer et al 2011).

The so called stinger on the Solenopsis invicta is actually a modified egg laying structure, or ovipositor. Because worker ants are sterile, being incapable of producing eggs, the ovipositor has been converted to a stinging apparatus connected to a poison glad which houses the ant's venom. The venom that the Solenopsis invicta utilizes contains two active components, alkaloids and proteins (Baer et al 2011).

The oily aliphatic substituted alkaloids is a necrotizing alkaloid meaning it induces premature cell death of effected tissue cells by autolysis, or self-digestion (Baer et al 2011). The dying cells attract the body's defensive white blood cells which accumulate and form a pustule.

If the skin around this pustule is broken due to scratching a secondary bacterial infection may occur which can require medical attention. The proteins found in the venom account for less than one percent of the mixture and have little to no effect on most people (Baer et al 2011). However a small proportion of people are highly sensitive to these proteins resulting in a major allergic reactions and anaphylactic shock.

Green Beard Gene

The term 'green-beard gene' is used in biology to describe a gene that results in a phenotypic response, giving rise to a detectable feature such as a green beard on the individual that possess such gene.

While Solenopsis invicta don't have green beards they do use this type of gene expression as a way to identify and kill certain queens within their nest (Keller 1998). In a nest of Solenopsis invicta all egg-laying queens are Bb heterozygotes at the locus Gp-9 with queens that are BB homozygous at this locus being killed off by worker ants (Keller 1998).

Research has determined that the allele Gp-9^b is the green-beard allele and is responsible for this phenomenon. Workers that are Bb heterozygous at this locus are reported to hunt out any queen initiating reproduction that is not also Bb heterozygous but rather BB homozygous (Keller 1998). Workers appear to distinguish between the BB and Bb queens on the basis of a transferable odor cue (Keller 1989). Homozygous and heterozygous queens both produced slightly different odors that can be detected and distinguished by the worker ants. If the odor of the homozygous BB queen is detected worker ants swarm and attack the queen to death. Subsequently, if any of the attacking worker ants picked up the queens odor on their own body, they too can be targeted and eliminated (Keller 1998).

Necrophoric Behavior

As with many ant colonies, the colonies of Solenopsis invicta have a system for discarding their waste and disposing of their dead. Waste material and uneaten food are taken by worker ants and placed in a designated pile, it is at this site that Solenopsis invicta also discard they bodies of dead ants. The process of disposing of dead worker ants is termed necrophoric behavior, and has been a topic of interest for scientists for a long time. Researchers Dennis F. Howard and Walter R. Tschinkel are two examples of such scientist. In 1976 they discovered the chemical mechanism that drove worker ants to transport and discard the corpses. As a result of decomposition fatty acids, such as oleic acid, accumulates in the recently deceased ant. Howard and Tschinkel hypothesized that this fatty acid accumulation was triggering a necrophoric response in the remaining worker ants.

To test this multiple experiments were done. First pieces of paper laced with synthetic oleic acid were introduced into nests of Solenopsis invicta. These bits of paper were later found discarded in the nest's trash pile, indicating that they stimulated necrophoric behavior (Howard & Tschinkel 1976). To further these findings Howard & Tschinkel also removed healthy worker ants from their colonies and applied a light layer of oleic acid on their body before they were returned to their nest. Like the oleic acid treated paper, it was recorded that these oleic acid treated worker ants were quickly seized and transported to the trash pile by other workers (Howard & Tschinkel 1976). Finally to prove that the fatty acids were the cause of this necrophoric behavior the researchers introduced freshly frozen Solenopsis invicta ants into a Solenopsis invicta nest. Unlike regular corpses, these frozen ants were left alone and did not stimulate necrophoric behavior due to the lack of decomposition leading to an accumulation of fatty acids (Howard & Tschinkel 1976).

Reference

Ascunce, M. S., C.-C. Yang, J. Oakey, L. Calcaterra, W.-J. Wu, C.-J. Shih, J. Goudet, K. G. Ross, and D. Shoemaker. "Global Invasion History of the Fire Ant Solenopsis Invicta." Science 331.6020 (2011): 1066-068. Web. 29 Nov. 2015.

Baer, Harold, T.-Y. Liu, Martha C. Anderson, Murray Blum, William H. Schmid, and Frank J. James. "Protein Components of Fire Ant Venom (Solenopsis Invicta)." Toxicon 17.4 (1979): 397-405. Web. 1 Dec. 2015.

"Can Orkin Control Fire Ants?" Orkin. Orkin, n.d. Web. 30 Nov. 2015.

Howard, Dennis F., and Walter R. Tschinkel. "Aspects of Necrophoric Behavior in the Red Imported Fire Ant, Solenopsis Invicta." Behaviour 56.1 (1976): 157-78. Web. 29 Nov. 2015.

Keller, Laurent, and Kenneth G. Ross. "Selfish Genes: A Green Beard in the Red Fire Ant." Nature 394 (1998): 573-75. Print.

Lebrun, Edward G., John Abbott, and Lawrence E. Gilbert. "Imported Crazy Ant Displaces Imported Fire Ant, Reduces and Homogenizes Grassland Ant and Arthropod Assemblages." Biol Invasions Biological Invasions 15.11 (2013): 2429-442. Web. 29 Nov. 2015.

MacGown, Joe. "Solenopsis Invicta Buren." Solenopsis Invicta Buren. Mississippi State University, 02 Oct. 2014. Web. 29 Nov. 2015.

"Red Imported Fire Ant Protection Program." Alohamrsfischer /. N.p., n.d. Web. 01 Dec. 2015. <http://alohamrsfischer.pbworks.com/w/page/100738072/Red%20Imported%20Fire%20Ant%20Protection%20Program>.

Wetterer, James Kelly. "Exotic Spread of Solenopsis Invicta Buren (Hymenoptera: Formicidae) beyond North America." Sociobiology 60.1 (2013): n. pag. Web. 29 Nov. 2015.