Parorectis Spaeth, 1901

Riley, Edward G., 2020, A new species of Parorectis Spaeth from the north-central United States, with notes on prothoracic and head morphology of the genus (Coleoptera: Chrysomelidae: Cassidinae: Cassidini), Insecta Mundi 2020 (808), pp. 1-9 : 2-3

Parorectis Spaeth, 1901

Orectis Spaeth 1901: 346 .

Type species: Cassida rugosa Boheman, 1854 , original designation, [not Lederer ( Insecta : Lepidoptera )].

Parorectis Spaeth 1901: 346 (as subgenus of Orectis ).

Type species: Cassida callosa Boheman, 1854 , original designation.

Generic diagnosis. The following combination of characters will distinguish the genus Parorectis among the New World genera of the tribe Cassidini : Prothorax with circum-foraminal ridge forming inner margin of antennal groove for reception of antennomeres 2–3 ( Fig. 7–10 : CFR); pleuron lateral to circum-foraminal ridge with elevated lateral ridge forming outer margin of antennal groove for reception of antennomers 2–3 ( Fig. 7–10 : LR). Elytron with anterior margin distinctly crenulate ( Fig. 6 ), disc tuberculate or strongly punctate. Pro-, meso- and metatarsal claw-pairs symmetrical in both sexes; each claw simple (without basal tooth), with basal angle rounded ( Fig. 21 : BA); pectens present ( Fig. 13 , 21 : PE), inconspicuous (micropectens) and symmetrical (equally developed on respective internal and external surfaces of each claw, as in Fig. 21 ). Claw segment (tarsomere IV) with lateral flanks not projected below claws.

Systematic position. Riley (1986) classified Parorectis with the other North American genera that possess crenulate anterior elytral margins, all claw-pairs symmetrical in both sexes, and pectens, when present, symmetrical.

Antennal grooves and circum-foraminal ridge. Parorectis has been reported to possess antennal grooves ( Borowiec and Świętojańska 2018 [in key]; López-Pérez and Zaragosa-Caballero 2018 [in key]; Riley 1986 [in key]; Riley et al. 2002 [in key]). This is a reference to what superficially appears to be a discontinuity or break in an anterior extension of the ridge forming the edge of the prosternal collar. The genera Deloyala Chevrolat and Chiridopsis Spaeth have similar apparent discontinuities accompanied by a groove-like channel at this position. This channel is wider and more strongly developed in these genera than in Parorectis . It is likely that living adults of all three genera are capable of flexing their antennae backward, seating the narrowest antennomeres (III and IV) in this channel or break. Among preserved specimens of Parorectis , only the occasional individual will have an antenna in this position.

In Parorectis , the circum-foraminal ridge is continuous and encircles the entire anterior prothoracic foramen, but almost all of it can only be viewed after removal of the head ( Fig. 7–10 : CFR). Scanning electron microscopy reveals that the true circum-foraminal ridge is accompanied by a fine line of setae ( Fig. 9–11 : CFR). The apparent discontinuity is not a break in the circum-foraminal ridge, but the result of a separate structure, a lateral ridge located laterad on the thoracic pleuron ( Fig. 7–10 : LR). The lateral ridges begin at the apparent break on each side of the anterior foramen, arch forward and ultimately dissipate anteriorly. They could easily be mistaken for part of the circum-foraminal ridge if the head were not removed. The origin of the lateral ridge, either an entirely novel structure or a detached and off-set anterior extension of the prosternal collar, is undetermined at this time. At the point of the apparent break, the anterior portions of the true circum-foraminal ridge extend upward on each side onto the ceiling of the foramen and arch forward to meet anteriorly. Basally, the circumforaminal ridge is located internal to the edge of the prosternal collar ( Fig. 10 : CFR). At its distal and uppermost point, the ridge is augmented by a smooth crescent-shaped, platform-like structure ( Fig. 7–11 : PL). This structure likely serves as the plectrum (scraper) of the stridulatory mechanism and possibly engages with the cephalic binding patch (see below).

Stridulation mechanism. A vertico-pronotal type of stridulatory device is said to be widespread among taxa of the Cassidinae , including the former Hispinae ( Schmitt 1991, 1994). This type of stridulatory mechanism consists of a presumed plectrum (scraper) located on the thorax and a pars stridens (file) located on the posterodorsum of the cranium. López-Pérez et al. (2018: table S1) recorded a stridulatory file in the male sex of 33 genera of Cassidini (this tribe including the Aspidimorphini and Ischyrosonychini ). In Parorectis , the platform-like crescent-shaped structure likely functions as the plectrum ( Fig. 7–11 : PL). Other than the circum-foraminal ridge, which is weakly developed at this position, there are no other structures on the ceiling of the anterior foramen that could serve as a plectrum. The pars stridens consists of an elongate patch of very fine transverse ridges that is tapered at both ends ( Fig. 3, 4 : PS). While the plectrum portion of the mechanism is present in both sexes in Parorectis , the pars stridens is only present in males; the corresponding location on the cranium is smooth in females.

The sexual dimorphism of the pars stridens, present in males and absent in females, raises the interesting question: what function does stridulation serve these beetles? It is unlikely that defense is the primary function of stridulation, although it could be a secondary function in males. More likely, the function of stridulation is somehow sexual in nature, probably involving male-to-male competition or male-to-female courtship behavior.

Cephalic binding patch. At the center of the cranial dorsal surface of Parorectis species is a dense patch of spicules located just anterior to the position occupied by the pars stridens. An inexperienced observer using normal light microscopy could easily mistake the reflectivity of this patch for a pars stridens. The individual spicules of the patch are short, pointed or multi-pointed, inclined forward, and their arrangement is confused ( Fig. 5 , 12 ). It is probable that head-to-thorax binding is the function of this patch; thus, the term cephalic binding patch is proposed here. This binding mechanism, however, is different from that of the better-known elytron-to-body binding patches where there are interdigitating patches on corresponding body parts ( Samuelson 1996). In Parorectis , there are no corresponding spicules on the ceiling of the anterior prothoracic foramen. The spicules of the cephalic binding patch likely engage with the thoracic surface including the structure here called the plectrum. In Parorectis , both males and females possess equally developed cephalic binding patches, and both sexes have a “plectrum” suggesting that the two structures function in head-to-thorax binding. Head-to-thorax binding, where the head can be withdrawn and locked in a safe position within the prothorax, is likely part of a broad suite of defensive behaviors in adult tortoise beetles.

Figures

Figures 1–8. Parorectis arenaria new species 1) Holotype and holotype labels. 2) Male head, face. 3) Male head, dorsum of cranium: BP = cephalic binding patch, PS = pars stridens. 4) Pars stridens. 5) Cephalic binding patch. 6) Base of pronotum and anterior margin of elytron. 7) Anterior prothoracic foramen with head removed, ventral view: AG = antennal groove, CFR = circum-foraminal ridge, LR = lateral ridge, PC = prosternal collar, PL = plectrum. 8) Anterior prothoracic foramen with head removed, ventrolateral view.

Figures 9–13. Parorectis arenaria new species, scanning electron microscopy images. 9) Anterior prothoracic foramen with head removed, ventral view. 10) Anterior prothoracic foramen with head removed, ventrolateral view: AG = antennal groove, CFR = circum-foraminal ridge, LR = lateral ridge, PC = prosternal collar, PL = plectrum. 11) Plectrum. 12) Spicules of cephalic binding patch. 13) Mesotarsal claws, lateral view: PE = pecten.

Figures 14–21. Parorectis arenaria new species, body parts. 14) Male antennae. 15) Male protarsus, lateral and dorsal. 16) Male genitalia, en-face view. 17) Male genitalia, lateral view. 18) Female genitalia tract and pygidium. 19) Female sternite VIII. 20) Spermatheca and adjacent duct: AP = appendix. 21) Male mesotarsal claws, exterior and interior surfaces of posterior claw on left, interior and exterior surfaces of anterior claw on right: BA = basal angle, PE = pecten.