The Canadian Hemiptera (Sternorrhyncha, Auchenorrhyncha, and Heteroptera) fauna is reviewed, which currently comprises 4011 species, including 405 non-native species. DNA barcodes available for Canadian specimens are represented by 3275 BINs. The analysis was based on the most recent checklist of Hemiptera in Canada (Maw et al. 2000) and subsequent collection records, literature records and compilation of DNA barcode data. It is estimated that almost 600 additional species remain to be discovered among Canadian Hemiptera.

Barcode Index Number (BIN), biodiversity assessment, Biota of Canada, DNA barcodes, Hemiptera , true bugs

The order Hemiptera, the true bugs, is a relatively large order. Worldwide there are an estimated 106,970 described species (Henry 2017, Bartlett et al. 2018, Hardy 2018). The recognised Canadian Hemiptera fauna (Table 1) has been greatly expanded since the review by Scudder (1979), with an increase of 937 species above the 3079 then known. The checklist of Canadian Hemiptera (Maw et al. 2000) provided comprehensive lists and distributions for all species recognised at that time. Here we present updated totals, including a number of additional unpublished records represented by specimens in the Canadian National Collections of Insects, Arthropods and Nematodes (CNCI) in Ottawa. Gwiazdowski et al. (2015) presented a detailed analysis of all Hemipteran DNA barcodes available for the Canadian fauna.

A further 590 species are estimated to occur in the country, with the majority expected in the large families Aphididae, Cicadellidae, and Miridae. Estimates of the number of unrecorded species for the less diverse families is based mainly on known but undescribed species and presence of species in adjacent climatologically and ecologically similar parts of the United States, and known distributions of host plants. Molecular data and analysis of host plant usage provides evidence of additional cryptic diversity in the more speciose phytophagous groups. For some families, presence of unnamed clusters in the DNA barcode data suggests additional species, assuming that in most cases Barcode Index Numbers (BINs), as defined by Ratnasingham and Hebert (2013), correspond to one or more species (Gwiazdowski et al. 2015).

The classification used here follows Psyl’list (Ouvrard 2018) for Psylloidea, Aphid Species File (Favret 2018) for Aphidomorpha, ScaleNet (García Morales et al. 2016) for Coccoidea, Bartlett et al. (2018) for higher classification of Auchenorrhyncha, Bartlett et al. (2014) for species level delimitation in Fulgoromorpha, Dmitriev (2018) for species level delimitation in Cicadomorpha, and Henry (2017) for higher level classification of Heteroptera. There have been several changes in higher level classification since Scudder (1979). Homoptera, no longer recognised as a formal taxon, is now treated as two suborders, namely Sternorrhyncha and Auchenorrhyncha. Although not followed here, some authors (after Sorensen et al. 1995) separate the Auchenorrhyncha into suborders Clypeorrhyncha and Archaeorrhyncha. Among Sternorrhyncha, many new families of scale insects have been erected; species in Canada formerly included in Margarodidae are now dispersed among Matsucoccidae, Steingeliidae and Xylococcidae; Putoidae was formerly included in Pseudococcidae. Schemes for the subdivision of family Aphididae, such as that of Heie (1980) (and used in the Hemiptera checklist of Maw et al. 2000), have been proposed, but largely ignored in the absence of a clear consensus on the relationships among aphid subgroups. Within the Fulgoroidea, the Acanaloniidae, Dictyopharidae, and Kinnaridae are now recognised in Canada, with their species removed from the Issidae, Fulgoridae, and Cixiidae, respectively. The broadly constituted Cercopidae has been divided, with most Canadian species now placed in the Clastopteridae and Aphrophoridae. In the Heteroptera, most former lygaeid subfamilies have been given family status so that Lygaeidae of Scudder (1979) is now represented by eight families (Henry 1997); the further segregation of Ischnorhynchidae and Orsillidae (Sweet 2000) from Lygaeidae is not recognised here. Lyctocoridae and Lasiochilidae have been separated from Anthocoridae. On the other hand, Aradidae now includes Meziridae, Miridae includes Isometopidae, and Reduviidae includes Phymatidae and Ploiariidae.

The 419 non-native species of Hemiptera represents a significant proportion of the total fauna. In Aphididae, about 19% of the species are non-native. An overview of the non-native aphid fauna of North America was provided by Foottit et al. (2006) and updated by Skvarla et al. (2017). The non-native Heteroptera of Canada (about 7% of the total fauna) were treated by Scudder and Foottit (2006).

Worldwide, the Sternorrhyncha are represented by about 18,690 species (Hardy 2018), with about 2950 species in North America (approximate composite number based on Foottit et al. 2006, García Morales et al. 2016, Skvarla et al. 2017, Mallory 2018, Ouvrard and Martin 2018). Currently, 1120 species of Sternorrhyncha are known from Canada compared to 834 in 1979, and it is expected that a further 215 species will be eventually found in the country (Table 1).

In Canada, the Aphididae and Adelgidae are relatively well known. Foottit and Maw (1997, 2014) contributed syntheses of the Yukon and grassland faunas of Aphididae. Aphids and adelgids are well represented by DNA barcodes (Foottit et al. 2008, 2009a, b), and, in general, barcode diversity in these groups corresponds well to morphological species concepts. However, several currently recognised aphid species are represented by more than one BIN, as defined by Ratnasingham and Hebert (2013). In two such cases, subsequent morphological analysis and addition of other genetic loci has resulted in the recognition of new species (Foottit et al. 2010, Foottit and Maw 2018). Conversely, members of several aphid species groups are not distinguishable by COI sequence divergence (Foottit et al. 2008).

The Psylloidea have not been subjected to extensive taxonomic or faunal analysis in Canada, except for work by Hodkinson (e.g., Hodkinson 1976) in British Columbia and Alberta. The identifiable forms of Coccoidea (adult female) and of Aleyrodidae (immatures) are sessile or subterranean and thus not captured by the usual general collecting methods. Consequently, the national fauna and regional distribution of species in these two groups are poorly known, and even limited efforts can yield new records. Kozár et al. (1989) identified several species of scale insects new to Canada based on brief collecting efforts in southern British Columbia. In a recent study of ant–sternorrhynch associations at a single grassland site in Alberta, two of the four species of Pseudococcidae found were newly recorded for Canada (Newton et al. 2011). The number of available BINs (see Table 1), largely based on untargeted sampling by the Biodiversity Institute of Ontario (University of Guelph), has indicated that current knowledge greatly under-represents the true fauna of Psyllidae and Aleyrodidae if BIN diversity can be considered a good approximation of species diversity in these groups.

Worldwide there are about 43,024 species of Auchenorrhyncha (Bartlett et al. 2018), but an estimate for North America is currently not available. In Canada, Hamilton (1997, 2014) analysed the cicadellid fauna of the Yukon and the Canadian Prairie Ecozone, respectively, Gareau (2008) documented that of Quebec, and Wilson (1997) treated the Yukon Delphacidae. The taxonomic status of several auchenorrhynch groups has been updated. A number of papers by Hamilton (e.g., Hamilton 1983, 1994, 1998) have revised many groups of Cicadellidae. As well, the large and difficult tribe Erythroneurini has been completely revised by Dmitriev and Dietrich (2007, 2009, 2010). The Cercopoidea were completely revised and a handbook published by Hamilton (1982). Progress on the Fulgoroidea includes a review of the North American fauna (Bartlett et al. 2014), which provides illustrated keys to all genera including the first comprehensive key to delphacid genera in the region. The known diversity of Canadian Auchenorrhyncha has increased since Scudder (1979), mostly as a result of taxonomic progress and improved knowledge of distributions. Currently, 1491 species are known from Canada compared to 1060 in 1979, and it is expected that a further 223 species will be eventually found in the country (Table 1). Most of the increases are in line with estimates of unrecorded species provided by Scudder (1979). The highest proportional increase is among the Cicadidae from nine to 21 recorded species; this increase is entirely due to improved knowledge of distribution (Hamilton 2010, Sanborn and Phillips 2013) as little taxonomic work has been done on the family in Canada. The highest numerical increase is among the Cicadellidae with an increase of 297 species; this is due to a combination of significant taxonomic research, greatly increased knowledge of distributions, and a small number of recently introduced species. We expect this family to hold the largest number of still unrecorded species (estimated at 150 species), particularly among the under-studied and under-collected subfamily Typhlocybinae.

Significant progress has been made in DNA barcoding of the Canadian Auchenorrhyncha. Data for 691 species have been released (Foottit et al. 2014, Gwiazdowski et al. 2015) and unpublished data for additional species is available in Barcode of Life Data System (Ratnasingham and Hebert 2007). A simple comparison between the number of BINs and recorded species suggests that more than half the Canadian species have been barcoded in most families, and an impressive 91% of the highly diverse Cicadellidae. However, caution is required in interpreting these numbers. Single BINs have been shown to include multiple morphologically distinct species in a number of cicadellid genera (Foottit et al. 2014). Conversely, preliminary examination of BINs for the Typhlocybinae suggests that single species may be represented by multiple BINs. Thus, the number of BINs may not be predictive of the number of distinct species within these groups.

There are about 45,254 described species of Heteroptera in the world. The most recent published comprehensive catalog for the group in North America (Henry and Froeschner 1985) includes 3834 species. About 1400 species are currently known to occur in Canada compared to 1171 in 1979, and it is expected that a further 151 species will be eventually added (Table 1). Most families of this suborder are relatively well known in the country. However, representatives of two families have been found in Canada only recently: Schizopteridae in 2010 (Scudder 2010a) and Aenictopecheidae in 2016 (Scudder and Štys 2016). Roch (2017) recently documented the Heteroptera of Quebec. Detailed analyses of the faunas of the Yukon, grasslands, Atlantic Maritime Ecozone and Montane Cordillera Ecozone have appeared (Scudder 1997, 2010b, 2011, 2014), and the aquatic and semiaquatic Heteroptera of Canadian peatlands and marshlands and the aquatic Heteroptera of the prairies and parklands were documented by Scudder (1987) and Scudder et al. (2010). Kelton (1980) provided a handbook of the Miridae of the Prairie Provinces. A major on-line database of the mirid fauna of North America (Schuh 2002–2013) includes records for a major portion of the holdings of the CNCI. DNA barcodes for the 334 species of Heteroptera drawn from CNCI (mainly Canadian species) were presented by Park et al. (2011) and reanalysed by Gwiazdowski et al. (2015).

The predicted number of Miridae constitutes the bulk of the estimate for Heteroptera overall, but this number is speculative and may be an underestimate if there are a significant number of undetected cryptic species within the more speciose genera.

Despite the significant increase in knowledge of Hemiptera in Canada since 1979, a substantial amount of the country’s biodiversity still awaits discovery. Some groups of Hemiptera are relatively well documented in Canada, while others are quite poorly known. However, even in the well-studied, but highly diverse phytophagous families (such as Aphididae and Miridae), there is probably unrecognised cryptic diversity associated with host plants and geographic variation. Several large genera in these families, such as Lygus, continue to present taxonomic difficulties (Schwartz and Foottit 1998) and opportunities for application of new approaches and technologies. Because many species of Hemiptera are current or potential pests, continuing research on detection, identification, quarantine and management of these groups will be required.

The express their thanks to Jeremy deWaard for updates to the number of available Barcode Index Numbers. We thank David Langor and Cory Sheffield for their critical comments.