Megalopsallus Knight, 1927

SCHUH, RANDALL T., 2000, Revision of the North American Plant Bug Genus Megalopsallus Knight, with the Description of Eight New Species from the West (Heteroptera: Miridae: Phylinae), American Museum Novitates 3305, pp. 1-70 : 2-5

Megalopsallus Knight

Megalopsallus Knight, 1927: 224 (n. gen.).

Merinocapsus Knight, 1968: 34 (n. gen.). NEW SYNONYMY.

Ankylotylus Knight, 1968: 55 (n. gen.; syn. by Schuh, 1986: 217).

TYPE SPECIES: Megalopsallus atriplicis Knight, 1927 .

DIAGNOSIS: Recognized by weakly flattend, lanceolate, silvery or white setae generally distributed on dorsum and thoracic pleuron, intermixed with pale or dark, reclining, simple setae (figs. 1C, 17D), elongate nearly parallel­sided body form in males contrasted with ovate body form of females (figs. 7–12), broad, usually short head in males (figs. 7–12), and small, relatively simple vesica of male genitalia (figs. 13–16) with apex blunt or as a single or bifid, short apical projection, and gonopore sclerite (when present) lacking barbs. Coloration often largely red or green, a few species castaneous, but then appendages often partly to entirely red. Known species feeding on halophytes, primarily members of Ephedraceae , Chenopodiaceae , and Solanaceae .

Megalopsallus was confounded by Knight (1968) with Europiella Reuter , but is easily distinguished by the more flattened body form in most species, the simpler, more delicate structure and much smaller size of the male genitalia, and the preference for halophytic hosts rather than members of the Asteraceae . Some dark­colored species, such as knowltoni and nigrofemoratus are similar in appearance to some Plagiognathus species , but are always separable by the form of the male genitalia; furthermore, most Plagiognathus spp. have only simple setae on the dorsum and elsewhere on the body. The pulvilli are sometimes large and cover most of the ventral claw surface in Megalopsallus (figs. 18C, 20D, but see fig. 17E), whereas in Plagiognathus the pulvilli are always small and cover only a small area near the base of the claw. As noted above, Knight’s (1927) characterization of pulvillar structure in Megalopsallus was in error.

REDESCRIPTION: Male: Small to moderately large species, total length 2.31–5.20, length apex clypeus–cuneal fracture 1.73–3.31, width across pronotum 0.83–1.32; usually elongate and more or less parallel sided (figs. 7–12). COLORATION AND VESTITURE: Coloration, including all appendages, ranging from totally pale, white, to almost totally black, often greenish or reddish. Vestiture of dorsum comprising reclining or recumbent, pale to dark, simple setae intermixed with white, silvery, or rarely somewhat golden, weakly to moderately flattened, usually lanceolate, sometimes woolly, setae (figs. 7–12), latter type also occurring on thoracic pleuron and abdominal venter. Tibial spines pale or dark, with or without dark spots at bases. STRUCTURE: Body form generally somewhat flattened; head broad, short longitudinally and clypeus not visible from above. Eyes sometimes bulging and removed from pronotal margin, more commonly conforming to curvature of frons and to anterior pronotal margin. Antennal segment 2 cylindrical (figs. 5, 6) or more rarely spindleshaped, especially in females (fig. 23). Hemelytra often elongate to strongly elongate and nearly parallel­sided, abdomen often reaching only to cuneal fracture, less frequently hemelytra not so elongate and body form elongate ovoid. Metathoracic scent­gland evaporatory area as in figs. 1B, 3B, etc.; mesothoracic spiracle with an elongate, conspicuous area of ‘‘mushroom bodies’’ dorsad of spiracle (figs. 3B, 4B). Claws ranging from relatively short and curving only near apex (fig. 1D) to relatively long and slender, smoothly curving over entire length (fig. 17E); pulvilli ranging from minute (fig. 17E) to large and covering nearly entire ventral claw surface (fig. 18C). Abdomen in males flattened dorsoventrally, broad basally and broadly curving and narrowing toward relatively small genital capsule (fig. 17B). MALE GENITALIA: Genital capsule and genitalia small relative to size of animal (fig. 17B); vesica formed of a single strap usually twisted to form an S shape (figs. 13, atriplicis ), more rarely forming a weak coil (fig. 13, brendae ) or not twisted and in the shape of a J (figs. 16, punctatus ); apex of vesica often sclerotized and attenuated, as either a single spine or bifid, sometimes membranous; (secondary) gonopore either apical or subapical, occasionally only weakly sclerotized; gonopore sclerite subtending gonopore often present and well sclerotized (figs. 13– 16, gs), never with barbs as in many Atractotomus species ; paramere and phallotheca typical of Phylini , without distinctive characteristics (figs. 14–16).

Female: Total length 2.28–3.98, length apex clypeus–cuneal fracture 1.74 –2.96, width across pronotum 0.96–1.42; often broadly oval to elongate ovoid and of more robust body form than males (figs. 7–12); antennal segment 2 of slightly smaller diameter than in males, sometimes spindle­shaped (fig. 23).

DISCUSSION: Comparison of the 29 species here recognized within Megalopsallus indicates that the continued treatment of Merinocapsus as a separate group almost certainly renders the former group paraphyletic. Therefore, Merinocapsus is treated as a junior synonym of Megalopsallus .

The affinities of Megalopsallus appear to be with Atractotomus Fieber , Knightomiroides Stonedahl and Schwartz , Phoenicocoris Reuter , Pinomiris Stonedahl and Schwartz , and possibly Chlamydatus Curtis , based particularly on the male genitalic structure, the genitalia being relatively small, the vesica being formed of a single strap, and the subapical secondary gonopore frequently being subtended by a gonopore sclerite (Kelton, 1965; Stonedahl, 1990; Stonedahl and Schwartz, 1996). Although several Megalopsallus species have the gonopore sclerite (figs. 13–16, gs) described by Stonedahl (1990), none have barbs on the sclerite. The apex of the vesica in Megalopsallus is usually attenuated, in the form of a single, short, simple spine, or is bifid. Atractotomus , Chlamydatus , and Phoenicocoris are Holarctic in distribution, whereas the other genera are restricted to the Nearctic.

In addition to the above described morphological differences, the host associations in Megalopsallus are distinctive within this related group of genera. Megalopsallus spp. are restricted to halophytes in the genus Ephedra of the primitive seed­plant group Ephedrales and among the angiosperms pri­ marily to several genera in the Chenopodiaceae and to the solanaceous genus Lycium . Knightomiroides , Phoenicocoris , Pinomiris , and some Atractotomus spp. feed on the Coniferales with the remaining Atractotomus spp. breeding on a variety of angiosperms; none are known to feed on the Chenopodiaceae , Solanaceae , or Ephedraceae (Stonedahl, 1990; Stonedahl and Schwartz, 1996).

A very few other Nearctic Phylini feed on halophytes. Among those that do is Tannerocoris sarcobati Knight, 1970 , which is found only on Sarcobatus , but which shows no obvious relationship with Megalopsallus on the basis of habitus or male genitalic morphology.

The Holarctic species Atomoscelis onustus (Fieber), 1861 , belonging to an otherwise Palearctic group, apparently feeds exclusively on ruderal chenopods; most Nearctic records of this species are as Atomoscelis modestus (Van Duzee), 1914 [see Kerzhner and Schuh, 1998, for synonymy with Atomoscelis onustus (Fieber) ]. The vesica of Atomoscelis appears always to be formed of a single strap basally, but is divided in two at the base of the secondary gonopore, a condition never seen in the species here assigned to Megalopsallus . Furthermore, Atomoscelis spp. are usually ovate and much less strongly sexually dimorphic than Megalopsallus spp.

A few other Palearctic Phylini merit examination as possible Megalopsallus relatives on the basis of morphology and/or host preferences. They are discussed here with the objective of determining whether Megalopsallus as a monophyletic group extends beyond the Nearctic.

Camptotylidea Wagner comprises 28 species (Konstantinov, 1999) occurring primarily in desert areas; many of them feed on chenopods. The vestiture of Camptotylidea is composed of only simple setae and the vesica is always extended apically well beyond the secondary gonopore, unlike the conditions found in all species here assigned to Megalopsallus .

Nasocoris Reuter from the Mediterranean and adjacent areas appears to feed exclusively on Ephedra (Schuh, 1995) , which might suggest a relationship with Megalopsallus . However, the clypeus is distinctively flattened and extended and antennal segment 1 is moderately to greatly elongate and clothed with long to very long more­or­less erect setae. The vesica appears to be formed of a single strap, as in Megalopsallus , and the genital capsule is relatively small. The general appearance and coloration of Nasocoris tesquorum Kerzhner are similar to those of Megalopsallus pallidus and the dorsal vestiture is also similar to that of Megalopsallus spp. (Wagner, 1973) .

Psallomimus Wagner , with one species in Egypt and the rest of its species further south in Africa (Schuh, 1995), has relatively small genitalia and the vesica is formed of a single strap as in Megalopsallus . However, the vestiture is always of simple setae, and the bugs are otherwise Plagiognathus ­like in appearance. The only known host record is from Solanum sp. (Linnavuori, 1993) .

Psallopsis Reuter has 15 described species from the Mediterranean, Middle East, and Central Asia; all breed on members of the Chenopodiaceae (Schuh, 1995) . Although host preferences in Psallopsis might suggest a relationship with Megalopsallus , the male genitalia indicate otherwise, the vesica being formed of two chitinous straps, rather than one as is the case in Megalopsallus (Wagner, 1975) .

In conclusion, it appears that Megalopsallus as here diagnosed is restricted to the Nearctic, and within that region to halophytic plant groups. My conception of Megalopsallus is relatively broad, because when treated otherwise the result would be several more difficult to diagnose genera.

Although Megalopsallus shows its greatest species diversity in saline environments in interior western North America, it also occurs in the eastern United States —primarily along the coastline—from Texas to Connecticut, and most recently has been recorded from coastal halophytes in the Dominican Republic. Unfortunately, eastern North American is relatively poorly collected and few host records are available, in stark contrast to the West where nearly all species have well­documented hosts.

The following key to species is designed for use with male specimens. For most species the description of coloration will also pertain to females, although table 1 will have to be consulted for measurements. For a few species it will be necessary to dissect the male genitalia to be confident of the identification. Sometimes host information will allow accurate identification of species such as humeralis and nigrofemoratus , which on the basis of external morphology and coloration may be virtually indistinguishable.

CHECKLIST OF SPECIES NAMES PROPOSED OR USED WITHIN MEGALOPSALLUS KNIGHT

adustus Knight, 1927 (Megalopsallus)