Tytthus Fieber

Henry, Thomas J., 2012, Revision of the Plant Bug Genus Tytthus (Hemiptera, Heteroptera, Miridae, Phylinae), ZooKeys 220, pp. 1-114 : 3-8

Tytthus Fieber

Tytthus Fieber 1864: 82. Type species: Capsus geminus Flor, 1860. Designated by Kirkaldy 1906: 128.

Cylloceps Uhler, 1893: 711. Type species: Cylloceps pellicia Uhler, 1893. Monotypic. Synonymized by Carvalho and Southwood 1955: 17.

Periscopus Breddin 1896: 106. Type species: Periscopus mundulus Breddin, 1896. Monotypic. Preoccupied by Periscopus Fitzinger, 1843 (Reptilia); synonymized by Carvalho and Southwood 1955: 17.

Breddiniessa Kirkaldy 1903: 13. New name for Periscopus Breddin, 1896; synonymized by Carvalho and Southwood 1955: 17.

Isoproba Osborn and Drake 1915: 533. Type species: Isoproba picea Osborn and Drake, 1915. Monotypic. syn. n.

Diagnosis.

Species of Tytthus are characterized by the small size (lengths ranging from 1.08 mm in brachypterous males of Tytthus wheeleri to more than 3.60 mm in Tytthus mundulus ), the relatively broad to nearly round head, usually with a pale yellow spot on the vertex bordering the inner margin of each eye; slightly protruding eyes not touching the anterior margin of the pronotum; smooth, shiny, trapeziform to campanulate pronotum, with lateral margins straight to weakly concave and moderately to strongly flared humeral angles; flat to weakly raised calli; subparallel hemelytra, often brachypterous or abbreviated, with the membrane and cuneus greatly reduced; slender claws with setiform parempodia; slender, tapered abdomen; small genital capsule; simple, C- to weakly S-shaped endosoma, lacking a secondary gonopore; mitt-shaped left paramere; and simple, round to elongate-oval right paramere.

Description.

Elongate subparallel to elongate oval species. Head shiny, impunctate, broader than long, sometimes becoming broadly rounded, especially in males, always slightly wider than anterior margin of pronotum; eyes prominent, more so in males, finely granulate, usually with scattered, fine, short setae; in dorsal view, frons and clypeus weakly rounded to prominent and pointed anteriorly; interocular space proportionately narrower in males (because of more prominent eyes) than females, nearly always with a small to large yellow or pale spot adjacent to inner margin of each eye; posterior margin nearly straight, with eyes nearly touching anterior margin of pronotum, to sometimes more narrowed behind eyes forming a necklike area more distinctly separating eyes from pronotum. Labium extending from bases of hind coxae to well onto abdomen near segment III or IV; segment I extending from base of head to bases of forecoxae. Antennal segment I shortest, stoutest; segment II longest; segment III longer than to subequal to segment IV. Pronotum shiny, impunctate, calli usually prominent, often with a glaucous sheen; subrectangular to trapeziform, especially in flightless brachypters, to strongly campanulate or bell-shaped in macropters. Mesoscutum broadly exposed in macropters; concealed by posterior margin of pronotum in brachypters. Scutellum well developed, equilateral. Hemelytra translucent, opaque white to bicolored with dark clouds, transverse bands, or extensive dark areas; macropterous or brachypterous, if only one sex brachypterous, always the female; fully macropterous hemelytra with each cuneus entire and membrane fully developed, extending well beyond apex of abdomen; brachyterous hemelytra (see discussion on brachyptery) abbreviated, ranging from a partially shortened membrane, extending only to apex of abdomen, to a strongly abbreviated membrane represented by only a remnant fringe on posterior edge of coleopteriform corium and clavus, with cuneus absent; in most extreme forms, only short hemelytral pads present, entirely lacking the cuneus and membrane, and extending only to abdominal terga III or IV. Lengths range in macropterous males from 2.14-3.42 mm; brachypterous males 1.08-1.28 mm; macropterous females 1.80-3.52 mm; and brachypterous females 1.44-1.68 mm. Ventral surface shiny, impunctate. Ostiolar evaporative area with a prominent auricle, curving posteriorly, gland opening large and distinct. Legs slender; femora unspotted, sometimes infuscated; tibiae slender, with or without distinct spines; tarsi slender, lengths of segment II and III subequal; claws elongate, slender, parempodia setiform.

Male genitalia: Endosoma relatively simple C-shaped to S-shaped, composed of a single, simple tube, often distally truncate or concave, lacking an apparent secondary gonopore. Left paramere mitt-shaped, with two arms and a narrow basal stem; right arm longest, widest, and most prominent, distally acute to rounded, gradually narrowing from base to apex, often broadened just before apex; left arm much shorter, distally acute. Right paramere elongate oval to nearly round, with a short basal stem. Phallotheca simple, sheathlike, exposed apex gradually narrowing from base to an acute apex.

Discussion.

Members of this genus are so superficially similar to species of the orthotyline genus Cyrtorhinus that Reuter (1875c) placed Tytthus , in synonymy under it, where it remained for the next 80 years. Even H. H. Knight (1923, 1925, 1931), North America’s most knowledgeable and prolific mirid specialist, failed to recognize the misplacement, and R. L. Usinger (1939), who treated several South Pacific species of Tytthus noted "An apparent structural anomaly in Cyrtorhinus which has not been given sufficient attention is the absence, in certain species, of arolia between the claws. The presence or absence and form of the arolia is usually a very reliable guide to relationships in Miridae ." Despite the character differences between these taxa, the species remained together under Cyrtorhinus until Carvalho and Southwood (1955) documented the obvious differences in male genitalia and pretarsal structure.

Another problematic genus, Isoproba Osborn and Drake (1915), has not been mentioned in the primary literature since its original description. Described to accommodate the only included species, Isoproba picea Osborn and Drake from Guatemala, it was said to be "readily separated from the [orthotyline] genus Paraproba Distant and allied genera by the more globose head and the peculiar shape of the thorax ( Osborn and Drake 1915)." Carvalho (1952, 1958), however, without explanation, transferred it to the tribe Dicyphini (then placed it in the subfamily Phylinae ), whose members also have generally rounded heads, as well as setiform parempodia. Cassis (1984) noted that he was unable to locate the holotype and, therefore, left it in Dicyphini with "considerable reservation."

I have studied the holotype of Isoproba picea deposited in the Ohio State University collection and, like most species included in the genus Tytthus , it has an overall shiny, fuscous to black head, pronotum, and scutellum, pale translucent hemelytra, and slender legs and antennae. The male genitalia are of the same type as for other species of Tytthus . The left paramere is mitt-shaped, the right paramere is relatively small, elongate oval, and simple, and the endosoma is slender and C-shaped. Isoproba picea differs from other species of Tytthus onlyin having a more distinctly rounded or bulbous head that is narrowed posteriorly into a short neck, especially in males, and the shallowly convex eyes hardly protruding from the side of the head. In addition, I have discovered that Tytthus hondurensis Carvalho (1984) is a junior synonym of Tytthus piceus . As a consequence, Isoproba is placed as a junior synonym of Tytthus .

Wing polymorphism: Slater (1975) separated the various types of wing modifications in the family Lygaeidae (sensu lato) into seven main categories: 1) Aptery (wings entirely absent); 2) Microptery (wings reduced to widely separated pads; 3), Staphylinoidy (wings have the clavus and corium indistinguishably fused into a coriaceous pad, and the wings meet evenly along the midline for their entire length, and usually cover only the first three abdominal segments); 4, Coleoptery (wings may or may not be reduced, but the coriaceous portion is not reduced but lengthened, the clavus and corium are fused, and the wings meet along the midline but do not overlap); 5) Brachyptery (clavus and corium either distinctly separate or fused, but shorter than in macropters, with only the inner portion of the membrane overlapping; 6) Submacroptery (clavus and corium always separate, with membrane slightly shortened, leaving the last abdominal segment exposed); and 7) Macroptery (wings unmodified, fully developed). Of the species of Tytthus exhibiting wing polymorphism, two can be categorized as staphylinoid ( Tytthus alboornatus , Tytthus wheeleri ), two as brachypterous ( Tytthus montanus , Tytthus piceus ), and four ( Tytthus balli , Tytthus fuscicornis , Tytthus pubescens , and Tytthus uniformis ) as submacropterous. The remaining sixteen species are known only from macropterous individuals.

Importance in biological control: It has been documented that most, if not all, species of Tytthus are specialized delphacid and, to a lesser extent, leafhopper egg predators. The best documented species, Tytthus mundulus , provides a good example of successful classical biological control (Hagen and Franz 1973, van den Bosch and Messenger 1973, Rosen 1985, Wheeler 2001). Frederick Muir (1920) discovered while searching for predators of the sugarcane delphacid in Queensland, Australia, that nymphs and adults fed on delphacid eggs. As a consequence, he brought Tytthus mundulus to Hawaii for release into the sugarcane fields. As Usinger (1939) noted, “Muir’s discovery that Tytthus (as Cyrtorhinus) mundulus (Breddin) lives exclusively on the eggs of the sugar-cane leafhopper, Perkinsiella saccaricida Kirkaldy, led to one of the most outstanding successes in the field of biological control of injurious insects." Zimmerman (1948) summed up the importance of this bug by saying "This one bug has saved the Hawaiian sugar industry and the Territory millions of dollars-its true worth can hardly be estimated."

Other species also have shown considerable potential in biological control. In South Africa, both Tytthus mundulus and Tytthus parviceps (Reuter) have been investigated for control of a tropiduchid, Numicia viridis Muir, on sugarcane ( Carnegie and Harris 1969). Although Tytthus mundulus was the better-known predator, Tytthus parviceps was more easily reared and showed the greatest potential for controlling Numicia viridis . Jhansi et al. (2002) studied the biology and prey preferences of Tytthus parviceps on planthoppers and leafhoppers on rice in India, including the brown planthopper, Nilaparvata lugens ( Stål). The Holarctic species Tytthus pubescens (Knight) and Tytthus pygmaeus (Zetterstedt) are known to prey on leafhoppers and delphacids in England ( Southwood and Leston 1959, Rothschild 1963, Wheeler and Henry 1992). In coastal eastern North America, Döbel and Denno (1994) considered Tytthus alboornatus (Knight) and Tytthus vagus (Knight) among the major predators of saltmarsh delphacids on two species of Spartina ( Poaceae ). For additional information on the hosts and habits of these predatory bugs, see the respective species within this revision.

Key to Species of Tytthus