A matrix-based Lucid^TM key is presented for the twelve genera of Monotomidae (Coleoptera: Cucujoidea) represented in the New World. A general overview is given for the features and technical specifications of an original interactive key for the identification of these genera. The list of terminal taxa included with the key provides a current summary of monotomid generic diversity for the Nearctic and Neotropical regions.

interactive key, data matrix, identification, morphology, LUCID, minute clubbed beetles

Matrix-based (also known as interactive, multi-access, multi-entry, or filter-style) keys offer vast advantages over traditional dichotomous identification keys. Some advantages include: freedom to follow more than a single path, ability to use only subsets of characters, integration of non-traditional (e.g., biology, distribution) and overlapping characters, effective use of multi-state characters, and inclusion of numerous graphics (Penev et al. 2009, 2012). These keys have been used successfully to overcome the challenges of identification of many groups of organisms, including various flies (Lyons and Dikow 2010; Ceretti et al. 2012), thrips (Mound et al. 2012), aphids (Favret and Miller 2012), and beetles (Lawrence et al. 2010; Lord et al. 2011; Nearns et al. 2016). However, many other challenging groups could use such powerful identification tools.

With 117 described species in twelve genera, the New World Monotomidae (also known as the “minute clubbed beetles”) are a small group of mostly mycophagous and predaceous beetles within the superfamily Cucujoidea. The worldwide generic diversity was last reviewed by Sen Gupta (1988). Since that review, nine new genera have been described, including one from the New World (Pakaluk and Ślipiński 1993; Pal 1996; Sen Gupta and Pal 1995). The North American genera were briefly reviewed and an identification key was provided by Bousquet (2002a). Many Nearctic genera have been reviewed relatively recently (Bousquet 1990, 2002b, 2003a, b, c; Bousquet and Laplante 1999). Despite these reviews, identification remains difficult, especially to non-specialists who are unfamiliar with the diagnostic characters. Since Monotomidae are important components of forest ecosystems as predators of scolytine bark beetles (Gregoire et al. 1985), vectors of fungal pathogens in trees (Hinds 1972), and pollinators (Jenkins et al. 2015), non-specialists frequently encounter them and need to make confident determinations. In addition, some monotomids, such as Rhizophagus parallelocollis, Monotoma longicollis, M. spinicollis, M. johnsoni, M. picipes, and others (Kuschel 1979; Bousquet 1990; Bousquet and Laplante 1999; Jelinek 2007), are being spread worldwide through human commerce or expanding their native range (Peck and Thomas 1998), and their effects on ecosystems will remain undocumented until they are identified. However, monotomid identifications have been complicated by the inaccessibility of taxonomic literature, lack of a recent, synthetic, genus-level treatment, and inadequacy of available graphics (habitus photographs, electron micrographs, and illustrations) to interpret many diagnostic features.

To address these issues, an interactive matrix-based identification key was developed for the twelve described genera of New World Monotomidae. This key is based on a matrix of 46 characters derived from morphometrics, discrete anatomical features, distributional data, and ecology. Included are illustrations of diagnostic features and dorsal and ventral photomicrographs of reliably determined representatives of each genus. Complete taxonomic coverage was possible for some genera, allowing inclusion of photomicrographs and morphometric data for all known species.

Application: Lucid Builder 3.5 (available at www.lucidcentral.org, see website for exact technical specifications and features list)

Key version: 1.0

Requirements for use: Java-enabled browser and internet connectivity

License for use of the key: Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Web location: http://www.monotomidae.com/MonotomidGen.html

The data underpinning the Lucid Key (Lucid Key files) reported in this paper are deposited in the Dryad Data Repository at http://dx.doi.org/10.5061/dryad.q9p4j

During development of this identification resource, several problems became apparent. First and foremost, nearly all monotomid genera included herein require modest or extensive taxonomic work. For the Nearctic region, the problem is not as serious because most genera, with the exception of Bactridium, have been at least partially treated within the last 25 years (e.g., Bousquet 1990, 2002a, 2002b, 2003a, 2003b, 2003c; Bousquet and Laplante 1999). Bactridium requires extensive work and is currently undergoing revision by TCM. In addition, most other genera represented in the Nearctic harbor some undescribed species (e.g., Monotoma, Aneurops, and Rhizophagus). As new types of data are examined, some currently recognized polymorphic species may be recognized as species complexes. The Neotropical fauna has been far less studied; numerous undescribed species and potentially even genera exist. Species identification in this region almost always requires comparison with type material. Even genus-level identifications of Neotropical specimens should be confirmed by a specialist, though this key will narrow down options for tentative determinations considerably.

Second, the relationships between monotomid genera are poorly understood. No phylogenetic analyses of any kind have been performed for this family. Thus, some morphological characters currently used to delimit genera require investigation to test their success in characterizing monophyletic groups. Some monotypic North America genera (e.g., Pycnotomina, Macreurops, and Phyconomus) should especially be targeted, as they may represent highly autapomorphic lineages nested within other genus-level clades.

Pending completion of a number of alpha taxonomic studies and phylogenetic analyses of the family, it will be possible to update this key to include species as the terminal units, and to more rigorously define the genera, as supported by additional characters. In the meantime, the numerous habitus images and illustrations should provide enough resources for confident genus-group determinations, and the other resources provided within MonotomidGen should facilitate approximate species identification.

This key provides a flexible, powerful, and media-rich information resource for any scientist or non-professional who needs to identify monotomid beetles. In addition, it provides a framework upon which to build future identification resources for this family. Eventually, a worldwide resource for identification of monotomid beetles should be completed to identify the species being transported around the world through human activities. This will allow for quicker identifications and therefore, quicker documentation of the spread of newly adventive species. Taxonomic resources of broader scope such as MonotomidGen can assist those tasked with discovering and identifying these anthropogenic species introductions.

This study was supported by a UGA CURO Research Grant (OFB & JVM), H.H. Ross Memorial Fund Grant (TCM), Ernst Mayr Travel Grant from Museum of Comparative Zoology at Harvard University (TCM), and CanaColl Foundation Endowment Fund Collections Grant (Y Bousquet & TCM).

We thank Darren Pollock (Eastern N.M. Univ.), Zach Falin (Univ. Kansas), Bob Turnbow (Enterprise, AL), the late Chuck Bellamy (CDFA), and Andy Cline (CDFA) for providing critical specimens for this study. Yves Bousquet, Nathan Lord, and Michael Thomas reviewed this manuscript and provided valuable comments and revisions. In addition, Lynette Elliott, Insect Images (Bugwood.org), Nathan Lord, Chris Mallory, the Pest and Disease Images library (PaDIL), Udo Schmidt, and Michael C. Thomas generously allowed their photos to be used for the Monotomidae diagnosis page. We would like to thank Floyd Shockley and David Furth (NMNH) for their assistance and hospitality, Gene Wright (UGA Lamar Dodd School of Art) for technical assistance, Zach McElrath for extensive coding and CSS support, and the UGA Department of Entomology for supporting this project.