Pariaconus Enderlein, 1926

Percy, Diana M., 2017, Making the most of your host: the Metrosideros-feeding psyllids (Hemiptera, Psylloidea) of the Hawaiian Islands, ZooKeys 649, pp. 1-163 : 18-21

Pariaconus Enderlein, 1926

Trioza Foerster, 1848: 82, in part.

Kuwayama Crawford, 1911: 503, in part.

Pariaconus Enderlein, 1926: 401. Type species: Kuwayama nigricapita Crawford, 1918, by original designation.

Adult colour and structure.

General body colour either entirely dark (black, brown, or red), entirely or mostly pale (cream, yellow or orange), or distinctly bicolored (pale/dark) (e.g. Fig. 4R). Overall size variable from ~1.5-4.5 mm in length (Fig. 4 E–G, J–R). Fore wing broadest either in the middle or in the apical third, membrane with or without distinct pattern of pigmentation, if without pattern either clear or fuscous (whiteish opaque in newly emerged adults); veins brown and either with trifurcation of R, M and Cu1, or vein R branching slightly anterior (Fig. 4A, this character can vary within populations and even between left and right wings of individuals and is not considered diagnostic for species); vein Rs relatively short, reaching fore wing margin at or proximal to M fork; long to minute setae on fore wing margins and veins; fore wing membrane either with spinules distributed densely throughout all cells or sparsely distributed and limited to a few cells; a cluster of marginal radular spines present in cells cu1, m1 and m2; fore wing apices either acute, bluntly acute, or rounded. Head moderately deflexed downwards, vertex more or less flat dorsally, with lateral ocelli lying on small tubercles, medial epicranial suture distinct; genal processes extremely short to long, and either concolorous, darker, or lighter than general body colour. Antennae short to long; antennal segments 10, with terminal 3(-6) segments usually darker; a single rhinaria apically on segments 4, 6, 8, 9; terminal segment with two unequal length setae. Distal proboscis segment short to long, darker apically. Thorax moderately arched. Minute to long setae on dorsum of vertex and thorax. Legs moderately short and robust to long and slender, tibia longer than femur; hind leg with meracanthus well developed and straight; metafemur with several stout setae apically; metatibia with a cluster of genual spines basally and typically 1+2 (occasionally a single or 1+3) sclerotized apical spurs and a comb of stout unsclerotized setae; tarsi subequal in length (Fig. 4 C–D, H). Male terminalia with more or less rounded subgenital plate; proctiger with moderate or more pronounced posterior lobe medially (interior surface of lobes bearing 4-5 simple setae, Fig. 4B), length shorter, subequal or longer than paramere; paramere variable; distal aedeagus segment apex either hooked or blunt. Female terminalia with proctiger short or long, dorsal surface straight, convex, or medially concave, subequal, shorter or longer than the subgenital plate, long dorsal setae, a simple anal ring composed of a continuous or interrupted double row of cells, and apex acute to bluntly acute; subgenital plate ventral surface either concave or convex, medium to long ventral setae, apex acute to bluntly acute or truncate; ovipositor either with or without serrations. Eggs highly variable, broadly ovoid or slender, pale or dark, with or without microsculpturing and striations, and with or without distinct pedicel and tail.

Immatures and biology.

Extremely variable immature morphology reflects variation in biologies and galling habits. Immatures may be free-living or gall forming (open and closed galls). Galling species appear to have one immature per gall/gall chamber, but in some galling species dense aggregations of galls result in clusters of chambers in close proximity. Morphologically consistent characters for 5th instars are antennae with 8-9 segments bearing 4 rhinaria (on segments 4, 6, 8 and 9, or 2 on segment 8) and two short to medium long terminal simple setae, tarsi with broad crescent arolia and each terminal tarsus bearing a long simple or weakly capitate seta, and anus situated ventrally.

Host plant.

The host plant of all Pariaconus species is considered to be Metrosideros polymorpha ( Myrtaceae ). However, there are five described species of Metrosideros in the Hawaiian Islands, and Pariaconus species and galls have occasionally been found on other Metrosideros taxa (e.g. Metrosideros macropus , Metrosideros rugosa , and Metrosideros waialealae ) (see Table 2), but in all cases, these Pariaconus species are predominantly on Metrosideros polymorpha . Extensive interspecies gene flow among Hawaiian Metrosideros suggests taxonomic concepts in Metrosideros may not reflect discrete genotypic or phenotypic units; the extensive morphotypic variation in Metrosideros polymorpha is therefore considered more influential in driving divergence than occurrence on different species of Metrosideros . Nevertheless, more detailed examination of population divergence in Pariaconus species found on multiple Metrosideros species remains to be undertaken.

Comments.

Enderlein (1926) erected this genus in order to rectify, as he saw it, the incorrect inclusion of three Hawaiian species ( Pariaconus nigricapitus , Pariaconus minutus , Pariaconus gracilis ) by Crawford (1918) in the predominantly new world genus Kuwayama based on the absence of genal processes (also referred to as genal cones or genae); Enderlein named this new genus Pariaconus , with the intention of highlighting this homoplasy: 'similarly without cones’, yet different from Kuwayama . The name Pariaconus has therefore existed since 1926 as the nomenclaturally correct name for these three Hawaiian taxa, but Pariaconus was not used in subsequent publications (e.g. Zimmerman 1948, Swezey 1954, Nishida et al. 1980), and the use of Kuwayama persisted until noted in a revisionary classification of the Psylloidea by Burckhardt and Ouvrard (2012).

The original placement of some taxa in Kuwayama by Crawford (who also originally described the genus Kuwayama ) was done with acknowledged reservations; characters used to define Kuwayama , such as the absence of genal processes (but with swellings below the bases of the antennae), enlarged clypeus, thorax as broad or broader than the head, and wing subacute to acute, are either not found at all, or not consistently found in Pariaconus . The reduced genal processes that are characteristic of the bicoloratus and minutus species groups are usually still visible between the bases of the antennae, and there are no distinct swellings below the antennae. Furthermore, the development of the genal processes in Pariaconus is highly variable and can even vary considerably within species (notably Pariaconus gracilis , Pariaconus oahuensis , Pariaconus ohiacola , and Pariaconus pele ). Diminutive genal processes are considered the ancestral condition based on data presented here, with development of longer genal processes in more recently derived species (e.g. the ohialoha group).

Pariaconus is a monophyletic genus endemic to the Hawaiian Islands. Four species groups within Pariaconus are recognized: the bicoloratus , minutus , kamua , and ohialoha groups. The taxa are morphologically remarkably diverse, making ancestral outgroup affiliations difficult to interpret, but they are neither allied to the type species of the genus Trioza , nor to Kuwayama . Nor are those members of Pariaconus that were originally assigned to Kuwayama by Crawford (1918) related to other Hawaiian taxa currently placed in Kuwayama that feed on Pisonia ( Nyctaginaceae ) and Sideroxylon ( Sapotaceae ) ( Caldwell 1940, Uchida and Beardsley 1992), nor are they related to other Hawaiian genera feeding on other plant families in the Hawaiian Islands. The Pariaconus species are the only psyllids that feed on the family Myrtaceae in the Hawaiian Islands, but they are not closely related to other Myrtaceae -feeding taxa in the Pacific or Australasia.

The original placement of some of the Pariaconus species in Trioza reflects the use of the genus Trioza as a default placement for triozid taxa with no clear affiliations. The width of the head in Pariaconus is typically greater ( bicoloratus and minutus groups) than that of the thorax, or subequal ( kamua and ohialoha groups), but the fore wings do not have the long sinuous Rs vein present in the type species of Trioza , Trioza urticae ( Linné, 1758), and Kuwayama , Kuwayama medicaginis (Crawford, 1910). The basal metatibial spur arrangement is typically 2+1 in Pariaconus , which is the same as Kuwayama medicaginis , but differs from the 3+1 in Trioza urticae . However, this character, normally considered fixed and di agnostic of species or even genera, can be variable within populations in Pariaconus (Fig. 4 C–D), with one population of Pariaconus hawaiiensis including individuals with a single spur, or 2+1, or 3+1. Similar variation was noted by Crawford (1918) for Pariaconus oahuensis and Pariaconus lanaiensis , see also note on this character in relation to Trioza eugeniae and Trioza adventicia .

In this study, broad species concepts are combined with the recognition of morphological forms (infrasubspecific names as per ICZN) to convey the extent and distribution of morphological variation. Some forms recognized here may warrant subsequent recognition at species level.

Adult key to Pariaconus species groups

Adult key to Pariaconus species in the bicoloratus and minutus species groups (found on Oahu, Molokai, Maui, Hawaii)