Canadian Journal of Arthropod Identification

An Illustrated Identification Key to Assassin Bug Subfamilies and Tribes (Hemiptera: Reduviidae)

CJAI 26 -- December 10, 2014

C. Weirauch, J.-M. Bérenger, L. Berniker, D. Forero, M. Forthman, S. Frankenberg, A. Freedman, E. Gordon, R. Hoey-Chamberlain, W. S. Hwang, S. A. Marshall, A. Michael, S. M. Paiero, O. Udah, C. Watson, M. Yeo, G. Zhang, J. Zhang

| Abstract | Introduction | Synopsis | Morphology | Identification Keys | Taxon Treatments | Acknowledgments | References | PDF | Cite |


With roughly 7,000 described species in 25 subfamilies, Reduviidae are one of the megadiverse families of insects and the third largest family within the order Hemiptera (after Cicadellidae and Miridae). Reduviidae, the assassin bugs, occur worldwide, but species-level diversity is clearly highest in the tropics of the Old and New Worlds and several subfamilies are confined to specific biogeographic regions (Froeschner and Kormilev 1989; Maldonado 1990; Cassis and Gross 1995). Assassin bugs occur in most terrestrial ecosystems and microhabitats, from mammal burrows in the Sonoran desert to decaying logs in the Bornean rainforest (Ryckman 1954; Miller 1959). Their morphological diversity is immense and evidently tied to the plethora of different life history strategies displayed by assassin bugs. A “typical” reduviid, such as many species of Harpactorinae or Reduviinae, is easily recognized as belonging to this family by layman and specialist alike, but skinny and sticklike Emesinae or the harpactorine tribe Rhaphidosomini can be mistaken for Berytidae or Hydrometridae and flattened Elasmodeminae deceptively resemble Aradidae, to name only 3 examples. Species in at least 7 subfamilies display contrasting warning coloration, but the great majority of species are drab colored, often matching color patterns in the microhabitats they occupy such as bark, leaf litter, or rock crevices. Many Reduviidae are fairly large-bodied, but overall body length ranges from an impressive 4 centimeters in species of Psyttala Stål to very small species of only about 2 to 3 millimeters, such as Tribelocodia Weirauch.

The great majority of assassin bugs prey on other arthropods and the range of morphological adaptations to prey capture is striking: Phymatinae, the ambush bugs, have evolved subchelate (foretibia clamps against distal process on forefemur) and chelate (foretibia folds back against incrassate forefemur) raptorial grasping legs, the long appendages of Emesinae allow them to steal from spider webs, and species in a clade of Harpactorinae have invented “flypaper” by coating their legs with self-generated sticky gland secretions. Even though natural history data for the majority of assassin bugs species are lacking, chance observations and dedicated studies have revealed a fascinating picture over the last century. It has become clear that Reduviidae display a remarkable range of prey specializations including predation on millipedes (Ectrichodiinae: Forthman and Weirauch 2012), termites (Salyavatinae, some Harpactorinae: McMahan 1982, 1983; Bérenger and Pluot-Sigwalt 2009), ants (Holoptilinae, some Reduviinae: Weirauch and Cassis 2006; Jackson and Pollard 2007; Weirauch et al. 2010), and spiders (some Emesinae: Wignall and Taylor 2011), in addition to vertebrate blood feeding that is restricted to the Triatominae (Lent and Wygodzinsky 1979; Schofield and Galvão 2009).

Reduviidae are also economically important and include both, destructive disease vectors and beneficial predators of insect pest species. All Reduviidae in the subfamily Triatominae (~140 spp., Schofield and Galvão 2009) feed on vertebrate blood, and as vectors of Chagas disease, pose a significant risk to human health. Chagas disease affects most Central and South American countries (Dias and Schofield 1999; Franco-Paredes et al. 2007; De Noya et al. 2010), is endemic in the United States, primarily as a zoonosis (Beard et al. 2003), and on the verge of worldwide dispersal due to human migration (Schmunis and Yadon 2010). More than 150 species of Reduviidae are predators of insect pests (Ambrose 1999) and several species are used as natural enemies, most importantly Pristhesancus plagipennis (Walker) as predator of cotton bollworm (Grundy and Maelzer 2000). Other species that are being explored for integrated pest management include species of Zelus and Sinea that feed, among others, on Lygus bugs, caterpillars and boll weevils (Cogni et al. 2002; Cohen and Tang 1997).

Despite serious taxonomic and phylogenetic efforts during the past 2.5 centuries, the classification of Reduviidae is far from being settled and numerous taxa at the level of genus, tribe, or subfamily are in need of modern systematic revisions. Peaks in taxonomic activity in Reduviidae occurred in the late 19th and early 20th century, spearheaded by the prolific Swedish entomologist Carl Stål as well as William Lucas Distant and Gustav Breddin. Four men, who together contributed >40% of all valid species names in Reduviidae, were the dominant figures in reduviid systematics around the middle of the 20th century: Norman Cecil Egerton Miller (London), Henri Schouteden (Brussels), André Villiers (Paris), and Petr Wolfgang Wygodzinsky (Rio de Janeiro, Tucumán, and New York). Two world catalogs (Putchkov and Putchkov 1986-1989; Maldonado 1990) are supplemented by regional catalogs (e.g., Cassis and Gross 1995) and catalogs focusing on the Phymatinae (Kormilev 1962; Froeschner and Kormilev 1989), a subfamily that was omitted from both world catalogs. Recent and ongoing taxonomic research on Reduviidae shows that there is no shortage of as yet undescribed species, but also emphasizes the need for comprehensive taxonomic revisions to reveal synonymies amongst described taxa (e.g., Bérenger 2006; Cai et al. 2003; Chlond 2011; Forero et al. 2004; Gil-Santana et al. 2000; Ishikawa and Okajima 2004; Melo and Coscarón 2005; Rédei 2007; van Doesburg and Pluot-Sigwalt 2007; Weirauch 2006).

The early higher-level classification of Reduviidae was mostly shaped by Charles Jean-Baptist Amyot and Jean-Guillaume Audinet Serville, who recognized many of the larger subfamilies. During the 20th century, numerous new subfamilies and tribes were established, with Wygodzinsky, Villiers, and Miller taking the lead on most of them. As opposed to Miller and Villiers, who described new subfamilies mostly on grounds of the species in question being “very different” and “difficult to accommodate in existing subfamilies”, Wygodzinksy’s approach was more synthetic and clearly informed by the Hennigian School of thought. Despite this, formal cladistic analyses of Reduviidae at the subfamily-level did not become available until the 1990s and beyond (Clayton 1990; Weirauch 2008; Weirauch and Munro 2009; Hwang and Weirauch 2012).

Published phylogenies using morphological (Weirauch 2008), molecular (Weirauch and Munro 2009; Hwang and Weirauch 2012), and combined datasets (Schuh et al. 2009) show high support for the monophyly of the family Reduviidae, with Pachynomidae recovered as their sister group. The monophyly of most subfamilies and some tribes has been tested in these analyses, and many are strongly supported (Hwang and Weirauch 2012). Interestingly, the situation for Triatominae, the only reduviid subfamily with medical importance, is not settled: different analyses found Triatominae to be polyphyletic (Paula et al. 2005), paraphyletic with respect to the Zelurus clade among Reduviinae (Hwang and Weirauch 2012), or monophyletic (Hypsa et al. 2002; Weirauch 2008; Weirauch and Munro 2009; Patterson and Gaunt 2010). Even more challenging are Reduviinae, the second largest assassin bug subfamily (~1,100 described spp., 145 genera): based on current analyses, Reduviinae are polyphyletic and fall into 11-14 clades, depending on dataset and analysis (Hwang and Weirauch 2012). Comparatively more minor issues are the potential polyphyly of Cetherinae (Hwang and Weirauch 2012), paraphyly of harpactorine tribes (Zhang and Weirauch 2013), uncertain delimitation of Ectrichodiinae with respect to Tribelocephalinae (Weirauch 2010), and potential paraphyly of Salyavatinae (Weirauch 2008). Another limitation is that 6 of the subfamilies have so far not been included in phylogenetic analyses. A comprehensive, combined morphological and molecular analysis of Reduviidae is now essential that will provide the phylogenetic framework and the diagnostic features for a meaningful re-classification of the family.

We realize that the classification of Reduviidae is on the verge of undergoing significant transformations. Nevertheless, we feel that it is valuable to provide identification keys and taxon treatments for the currently recognized 25 subfamilies, most importantly because many of these taxa will persist after re-classification. Existing identification keys to subfamilies of Reduviidae are outdated and therefore incomplete (e.g., Usinger 1943; China and Miller 1959), have a regional focus (e.g., China 1940), or fail to correctly key out a number of species (e.g., Schuh and Slater 1995). In addition, the now available wealth of digital images of live bugs in their natural environment and recent advances in imaging systems of preserved specimens allow, for the first time, the creation of very well-illustrated subfamily identification keys and taxon treatments. The subfamily-level keys are complemented by keys to the tribes of 5 subfamilies. We omitted a key to tribes of Emesinae, because we could not obtain photo-quality specimens for certain key taxa (please refer instead to the comprehensive tribal-level key provided by Wygodzinsky [1966]). The keys are followed by taxon treatments that provide, for each subfamily, diagnostic features, notes on taxonomy and distribution, a comment on taxa occurring in Canada, natural history notes, and a short, up to date, bibliography. The great majority of images of live assassin bugs were contributed by one of the authors, shot at various locations and using different photographic equipment. Digital images of preserved specimens were mostly taken in the Weirauch Lab using imaging systems by Microptics USA, GT Vision, and Leica Microsystems.