Dolichoderus thoracicus

This species is, in a simple sense, the most common and widely distributed Dolichoderus species in southeast Asia. Yet the form subsumed under this name appear to include a number of species that show consistent ecological and life history differences but are hard to distinguish morphologically (see the nomenclature section below).

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia, Philippines, Singapore, Sulawesi. Oriental Region: Cambodia, India, Laos, Thailand, Vietnam. Palaearctic Region: China.

Biology
Dill (2002):

(all references prior to 1989 referring to Dolichoderus bituberculaltus auct.) Emery 1887: 254 [Java: in Dischidia rafflesiana Wallich, parabiosis with Crematogaster sp.]; Kershaw 1905 [with aphids, interaction with aphidophagous lycaenid Miletus chinensis (Felder)]; Forel 1909: 226 [in carton nests]; Jacobson 1909: 121-122 [nests between leaves, in rolled leaves or underneath banana leaves, partly built with fragile]; Meijere 1909: 173 [Java: with membracids, feeding of myrmccophilous Diptera with fluid from ]; Roepke 1910 [Java: with (L.) (Lycaenidae)]; Jacobson 1911 [Java: variable nesting behaviour, often between joint leaves; trophobiosis with aphids, coccids, membracids; prey Ptilocerus ochraceus Montandon (Reduviidae)]; Emery 1912: 13, pl. 2, fig. 1. [illustration of carton nest]; Forel 1913: 90 [Malay Peninsula: in termite nest; Java: in termite nest; Malay Peninsula: in nest of Macrotermes gilvus (Hagen)]; Roepke 1918 [Java: large, dense trophobiotic assemblies with Ebhul varius (Walker). Planococcus lilacinus (Cockerell) (Pseudococcus crotonis auctt.) and Cerataphis lataneae Bsdv.; Miletus boisduvali (Moore) (Lycaenidae) lives in thoracicus nest]; Roepke 1925 [Java: larvae and pupae fall prey to Hypophrictoides dolichoderella Roepke (Tincidae) inside nest; frequent nest migrations]; Karawajew 1926: 426 [Java: workers in whitish, silken web underneath leaves of Amherstia nobilis Wallich where they also lend scale in sects; large trail with workers and dealate queens]; China 1928 [Java: fall prey to Ptilocerus ochraceus (Reduviidae), illustration]; Karawajew 1928: 307-308 [nests mostly built of very fragile carton, but in Java multichambered pavilions on leaves out of stabile carton (fig. 5, pl. 1)]; Menozzi 1932: 7 [Sumatra: nest presumably in tree Artocapus sp.; holding coccid larvae (Monophlebinae, ? Steatococcus Ferr.) in mandibles]; Franssen 1937 [Java: with Dysmicoccus brevipes (Cockerell), carries young larvae instars of Dysmicoccus]; Sonan 1939 [Taiwan: inside houses]; Wheeler 1942: 212 [Sri Lanka and Java: in hollow twigs of Triplaris americana Vahl, common species); Wirjati, 1958: 17 [Java: with Pseudococcus dorsospinosus Wirjati]; Franz 1975a: 412, 1975b: 265 [Java: most common ant species of Java; trophobiosis with pseudococcids and lecanines; building pavilions as shelter for these trophobionts; flexible nesting behaviour; polygynous]; Seeley et al. 1982 [Thailand: interaction with Apis florea and A. dorsata]; Veeresh 1990: 19 [India: trophobiosis with aphids and coccids on crops]; Rohe 1991 [Malay Peninsula: polygynous; large colonies (> 20,000 workers); nest in cavities and between leaves, partly usage of fragile carton material; trophobiosis with aphids, pseudococcids, coccids, and membracids; collecting bird faeces and dead insects, visiting extrafloral nectaries]; Rosciszewski 1995: 44, 56 [Malay Peninsula, lowland rainforest: nest in hanging dead wood; polygynous].

The following papers deal with the usage of D. thoracicus in pest control, mainly against species of Helopeltis (Miridae) in cocoa plantations in Southeast Asia (Java, Malay Peninsula, Sumatra), and partly also contain data on the general biology and life history of D. thoracicus: Van der Goot 1916, 1917; Meer-Mohr 1927; De Jong 1934; Wijnschenk Dom 1934; Betrem 1950; Giesberger 1983 [review]; Azhar 1985; Ia 1985; Bakri et al. 1986; Chong 1987; Ang 1988; Khoo & Chung 1989; Wat & Khoo 1989; Graham 1991; Way & Khoo 1991; Ho 1991; Azhar 1992 [control of Conopomorpha cramerella]; Heirbaut & Van Damme 1992; Khoo & Ho 1992; Mohamed & Mardi 1992; Way & Khoo 1992 [review]; Tuck 1994; [brief summary of biological information drawn from these papers: large colonies (trails reaching across several hectares); polygynous; nests in dark, dry places such as leaf litter, dead wood, cavities, folded leaves etc., partly using some carton material; arboreal as well as on the ground; in Indonesia (but not in Peninsular Malaysia) carton pavilions for trophobionts; prefers arboreal trails; trophobiotic associations with a variety of Hemiptera (e. g. Pseudococcidae: Cataenococcus hispidus (Morrison), Maconellicoccus hirsutus (Green), Planococcus lilacinus (Cockerell), Pseudococcus elisae Borchsenius, now known to be P. jackbeardsleyi Gimpel & Miller Coccidae: Coccus viridis (Green), Aphidoidea: Toxoptera aurantii (Boyer de Fonscolombe), Membracidae: Ebhul varius (Walker); defense of trophobionts against parasitoids; honeydew as main part of diet, supplemented by various nutrition: plant material, bird feces, eggs of Helopeltis; only infrequent foraging off the trails; not aggressive predators; competition and territorial conflicts with Oecophylla smaragdina (Fabr,) and Anoplolepis gracilipes (A. longipes auct.)].

Dolichoderus thoracicus, together with Anoplolepis gracilipes and Oecophylla smaragdina, is one of the most common ant species which tends honeydew-producing hemipterans in Indonesia. Fanani et al. (2020) examined the influence of these species on the introduced parasitoid Anagyrus lopezi, a species used to control the invasive cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae). They found that when ants were absent the average time spent foraging by individual parasitoids was significantly longer (27.39 minutes) compared to when ants were present (2.47- 4.68 minutes). As a result, parasitoids spent less time in finding hosts and a longer time in handling hosts. This resulted in more oviposition activities and a 2-3 fold increase in parasitism and the number of wasps that emerged from their hosts.

Jitjak & Sanoamuang (2019) describe a symbiotic relationship between the fungus and D. thoracicus in Thailand. The fruiting body of the fungus forms a cavity structure containing debris. They found these cavities function as nest sites for the ants. Even in mature fungal samples, which are naturally degraded with exposed carton-like structure, ants were still observed nearby. D. thoracicus is an indigenous species widely populated throughout South East Asian region including Thailand, and are capable of forming nests in a variety of substrates such as soil, leaves and plant cavities, and secrete sticky honeydew like other insects. The ants utilize the fungal fruiting body as nests, the hard and tough structure of the fungus protecting the ants from an otherwise harsh environment. Furthermore, the ants secrete feces or honeydew which could benefit the fungus’ growth and development.

Nomenclature

 *  thoracicus. Tapinoma thoracica Smith, F. 1860a: 69 (w.) INDONESIA (Sulawesi). Combination in Dolichoderus: Dalla Torre, 1893: 162; in D. (Hypoclinea): Emery, 1913a: 14. Senior synonym of bituberculatus (and its junior synonym sellaris): Donisthorpe, 1932c: 457; Shattuck, 1994: 70. Current subspecies: nominal plus bilikanus, borneonensis, lacciperdus, levior, nasutus, rufescens (unresolved junior homonym). See also: Shattuck, 1994: 70.
 * bituberculata. Hypoclinea bituberculata Mayr, 1862: 705 (w.) PHILIPPINES. Emery, 1887a: 254 (q.); Karavaiev, 1926d: 426 (q.); Wheeler, G.C. & Wheeler, J. 1951: 174 (l.); Imai, Brown, et al. 1984: 68 (k.). Combination in Dolichoderus: Emery, 1887a: 254; in D. (Hypoclinea): Emery, 1894c: 229. Senior synonym of sellaris: Mayr, 1867a: 76; of emarginata: Xu, 1995a: 35. Junior synonym of thoracicus: Donisthorpe, 1932c: 457; Shattuck, 1994: 70. See also: Bingham, 1903: 295.
 * emarginata. Dolichoderus (Hypoclinea) bituberculatus var. emarginata Santschi, 1920h: 168 (w.) LAOS. [Also described as new by Santschi, 1924c: 108.] Subspecies of thoracicus: Shattuck, 1994: 70. Junior synonym of bituberculatus: Xu, 1995a: 35.
 * sellaris. Hypoclinea sellaris Roger, 1863a: 213 (w.) SINGAPORE. Junior synonym of bituberculatus: Mayr, 1867a: 76.

Taxonomic Notes
Dill (2002) - D. thoracicus obviously is the most common and most widely distributed Dolichoderus species of Southeast Asia. As already stated by Donisthorpe (1932), D. thoracicus is the senior synonym of Mayr’s D. bituberculatus. Despite this early synonymization, this species had usually been identified and described as D. bituberculatus until the 1980s. D. thoracicus is part of a taxonomically very difficult complex consisting of many very similar species or subspecies, some of which are still undescribed. While a clear delimination of these forms based upon morphological characters is very difficult, there are in some cases very obvious biological or ethological differences. For example, the rather rare Dolichoderus sp., with the very distinctive habit of building pavilions out of spider silk (Maschwitz, Dumpert et al. 1991, corrected in Dumpert 1994) also belongs morphologically to this complex. Even the Dolichoderus referred to as “D. bituberculalus” in older works seems to fall apart into groups with rather distinctive biological traits. For instance, some have rather loose nests with or without fragile carton, while the nests of others are very stabile, multi-chambered out of firm carton material. Again, certain groups build stable-nest pavilions on leaves out of carton or silk (see review of literature on biology above).

While, on the one hand, the thoracicus complex seems to consist of various, still unidentified sibling species, there are, on the other hand, several existing taxa that most probably should be lumped. The majority of the many described subspecies is based only on very variable characters, stich as colour or very slight differences in the sculpturing or shape of the propodeum, which may not stand the test of a critical review. Furthermore, a synonymy with thoracicus has been already assumed for Dolichoderus gibbus by Emery (1889, 1901) and for Dolichoderus lactarius by Donisthorpe (1932). A thorough taxonomic review of this complex appears to be urgently indicated, not at least because of the frequent occurrence, wide distribution and considerable economic importance (e. g. usage in biological pest control) of these ants.

Type Material
Dill (2002) - Workers, Sulawesi: Makassar (A. R. Wallace).

Tapinoma thoracica

Two worker syntypes in. Labelled “Mak.”