Sociobiology 60(1): 1-10 (2013)
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Sociobiology 60(1): 1-10 (2013) Sociobiology An international journal on social insects REVIEW A Review of the Biology, Ecology and Behavior of Velvety Tree Ants of North America R Hoey-Chamberlain, MK Rust, JH Klotz University of California Riverside, Riverside, CA, USA Article History Abstract Edited by: Ants belonging to the genus Liometopum are regionally distributed across North Ame- Kleber Del-Claro, UFU - Brazil rica, Europe and Asia. L. apiculatum Mayr, L. luctuosum Wheeler, and L. occidentale Received 24 October 2012 Initial acceptance 27 November 2012 Emery are found in western North America and are referred to as velvety tree ants. Final acceptance 19 February 2013 Very little is known about the biology of these species, but they are similar. They are typically associated with trees and shrubs and are frequently found tending hemipte- Keywords rans. All three species are easily disturbed and resort to highly aggressive behaviors Liometopum apiculatum, Liometopum including the use of strong alarm odors. The following review is intended to summarize luctuosum, Liometopum occidentale the literature regarding the biology and control of these species. Special emphasis has Corresponding author been given to factors that might be important in their control and gaps in our current Michael K. Rust knowledge. Department of Entomology University of California Riverside Riverside, CA 92521-0314 E-Mail: [email protected] Introduction L. luctuosum and L. occidentale are often mistaken for carpenter ants (Camponotus spp.) by homeowners and Pest The genus Liometopum consists of 9 fossil and 8 ex- Management Professionals (PMPs). This mistaken identity tant species scattered over North America, Europe and Asia is due to morphological and behavioral characteristics they (www.antcat.org/catalog/329538). There are three North share with carpenter ants; namely polymorphic workers, American species, found in the western U.S. and Mexico: a smooth convex thoracic profile, and the tendency to L. apiculatum Mayr, L. luctuosum Wheeler, and L. occiden- excavate wood (Klotz et al., 2008). L. luctuosum are also tale Emery. The genus Liometopum belongs to the subfa- often confused with the T. sessile since they have the mily Dolichoderinae, which also includes other important same coloration, are similar in size, and produce an alarm structural pest ants such as the Argentine ant, Linepithema pheromone with a very similar odor. Consequently, their humile (Mayr), and the odorous house ant, Tapinoma sessi- importance as structural pests may be greatly under reported, le Say. According to Del Toro et al. (2009), Liometopum is especially in California, Oregon, and Washington. only a “minor pest in and around rural housing areas” and All three North American species are easily disturbed “no severe damages to housing or property have been re- and when aggravated, they resort to highly aggressive ported,” although the “uncomfortable bite and smell of this defensive behaviors, biting and releasing strong alarm ant makes it a nuisance to affected residents.” However, odors from their anal glands (Del Toro et al., 2009). They structural damage has been reported for two species, L. luc- produce a noxious alarm pheromone (described as smelling tuosum and L. occidentale (Wheeler & Wheeler, 1986; Me- like rotten coconut or having an intense butyric acid-like rickel & Clark, 1994; Gulmahamad, 1995; Hedges, 1998; odor). This pheromone consists of 6-methyl-5-hepten-2- Klotz et al., 2008). Homeowners commonly complain of the one, acetic acid, n-butyric acid, and 3-methylbutyric acid odor associated with an infestation of velvety tree ants. (isovaleric acid) (Casnati et al., 1964). Alarm pheromones Open access journal: http://periodicos.uefs.br/ojs/index.php/sociobiology ISSN: 0361-6525 2 R Hoey-Chamberlain, MK Rust, JH Klotz - Velvety Tree Ants of North America of many dolichoderines seem to be less species-specific than is oak forests found around 2000 m. At higher elevations olfactory sex attractants and other pheromones. For instance, they are found in pinyon pine zones, up to the ponderosa the alarm pheromones of Forelius pruinosus (Roger), pine and riparian zones; at lower elevations they inhabit Dolichoderus bispinosa (Olivier), L. occidentale, and T. creosote bush scrub and grasslands in microhabitats of clay, sessile will mutually affect one another. In L. occidentale under rocks, boulders, and decaying logs (Del Toro et al., this pheromone originates in the anal gland (Wilson & 2009). They have also been found in foothill meadows, de- Pavan, 1959). ciduous canyon forests, pinyon-cedar woodlands, ponderosa In Mexico, colonies of Liometopum have been used pine-cedar-oak woodlands, and cottonwood-willow forests as a food resource by people in rural areas for centuries. (Mackay & Mackay, 2002). At high elevations, their abun- The immature stages of the reproductive caste, known as dance decreases and they are replaced by L. luctuosum (Del “escamoles” are consumed and are a high-quality source of Toro et al., 2009). Altitude may play an important role in the protein, carbohydrates, and lipids. Adult reproductives may distribution of Liometopum. In regions of Mexico explored also be consumed by humans during swarming, and worker by Conconi et al. (1983b), L. luctuosum and L. apiculatum brood is consumed when other stages are scarce (Ramos- are only found between 2000 and 3000 m. Although condi- Elorduy & Levieux, 1992). Consequently, considerably tions below 1800 m looked favorable, they are absent. In the more is known about the biology of L. apiculatum than any U.S., L. apiculatum is found from 1316 to 2438 m. of the other species. Liometopum luctuosum has been reported at eleva- tions as low as 59 m (Dr. Laurel Hansen, Spokane Commu- Taxonomy nity College, personal communication, Sept. 6, 2012), but is typically found at elevations higher than 2400 m in more Liometopum occidentale was originally described southern latitudes (Wheeler & Wheeler, 1986; Del Toro et as Liometopum microcephalum var. occidentale by Emery al., 2009). The range of elevation of this species by state is (1895). Wheeler (1905) relocated it to a variety of Liometopum as follows: WA: 59-724m, ID: 664-786m, OR: 277-454m, apiculatum. It was finally elevated to the species level by CA: 1280-1596m, and NV: 1372-2469m (Dr. Laurel Hansen Wheeler (1917) and remained there in a recent taxonomic personal communication, Sept. 6, 2012, personal collection) review by Del Toro et al. (2009). and above 2000 m in New Mexico (Mackay & MacKay, Liometopum luctuosum was originally named 2002). Their range extends from temperate habitats as far Liometopum apiculatum subsp. luctuosum by Wheeler north as British Columbia (Canada), and to more arid habi- (1905) and Forel (1914). Creighton (1950) relocated it to tats of Central Mexico and western Texas. They inhabit pine, a subspecies of Liometopum occidentale. It was elevated oak, Douglas fir, and juniper forests, sagebrush, and high- to the species level by Wheeler & Wheeler (1986), and elevation riparian habitats (Conconi et al., 1987a; Clark & subsequently confirmed by Mackay et al. (1988) and Del Blom, 2007). This species is often strongly associated with Toro et al. (2009). but not limited to pine trees (Del Toro et al., 2009). Liometopum apiculatum was first described by Mayr Liometopum occidentale is found from sea level to (1870), who described the workers of this species. Emery over 1840 m in coastal regions from southern Washington (1895) later described the queens of this species; Wheeler to northern Mexico (Snelling & George, 1979; Del Toro et (1905) described the males and Wheeler & Wheeler al., 2009; Wang et al. 2010; Dr. Laurel Hansen, personal (1951) described the larvae. Shattuck (1994) considered L. communication, Sept. 6, 2012). The range of elevation of apiculatum a senior synonym of Liometopum masonium. this species also appears to depend on latitude with ants col- This species was also confirmed by Del Toro et al. (2009). lected from locations in Oregon as low as 7 m and up to Caution should be exercised when examining the 1700 m in California (WA: 31-142m, OR: 7-348m, CA: 142- literature prior to the review by Wheeler and Wheeler (1986) 1713m; Dr. Laurel Hansen, personal communication, Sept. in regards to L. luctuosum. However, L. luctuosum has only 6, 2012, personal collection). They are the most common been reported in the southwestern U.S. and not Mexico. and dominant ant in oak and pine forests of southwestern Workers of L. luctuosum are significantly smaller (n = 38, U.S. (Wheeler & Wheeler, 1986; Ward, 2005; Del Toro et 0.91 - 3.53 mg) than L. occidentale (n=40, 1.44 - 5.24 mg). al., 2009). They prefer to nest in the crevices of oaks, al- ders, elms, cottonwoods, and creosote, in soil, underneath Habitat/distribution bark of dead trees, and under rotten logs (Cook, 1953). Cook may be in error claiming that these are nests since we often Liometopum apiculatum ants are found in arid and see many, many adult workers in ‘resting places’ which are semi-arid regions of southwestern U.S. and Mexico to Quin- mistaken as nests, as noted by Klotz et al. (2008). tana Roo (Del Toro et al., 2009). They extend from Colorado Within their distribution range, the elevations at through Texas, New Mexico, southeastern Arizona, and south which Liometopum are found decreases the further north the into Mexico (Gulmahamad, 1995). They are usually found at location. To definitively demonstrate that there is an effect of elevations between 1000 and 2500 m, but their prime habitat latitude on the elevation at which Liometopum is distributed Sociobiology 60(1): 1-10 (2013) 3 in North America, a larger collection of these ants must be onies may contain as many as 250,000 individuals. Colonies made. remain useful for repeated brood collection by humans for 4 to 12 years (Ramos-Elorduy & Levieux, 1992). Nests Colony foundation in L. apiculatum is by haplomet- rosis (non-cooperative), that is, a single fertile queen founds Nests of L.