Stictolobus minutus ( Funkhouser, 1915 )

A. G. Wheeler, Jr. & Rothschild, Mark J., 2020, Do Nymphs Of The Treehopper Stictolobus Minutus (Funkhouser) (Hemiptera: Membracidae) Specialize On Grasses?, Proceedings of the Entomological Society of Washington 122 (1), pp. 211-234 : 216-221

Stictolobus minutus ( Funkhouser, 1915)

( Figs. 3–10 )

1830 Membracis subulata Say (junior primary homonym of subulata Weber, 1801 , but no available substitute name)

1852 Thelia (?) subulata: Walker

1890 Ceresa subulata: Provancher [probable misidentification]

1892 Ceresa subulata (?): Harrington [probable misidentification]

1894 (?) Stictocephala sublata [sic]: Goding

1908 Stictocephala (?) subulata: Van Duzee

1915 Stictocephala minuta Funkhouser (synonymized by Caldwell 1949) 1916 Stictolobus subulatus: Metcalf 1951 Stictocephala minuta: Funkhouser 1951 Stictolobus subulatus: Funkhouser 1965 Stictolobus minutus: Metcalf and Wade

Taxonomy.—The nomenclatural history of Stictolobus minutus involves homonymy, synonymy, disagreement regarding the proper generic name ( Van Duzee 1908), and imprecise nomenclatural actions. Say’s (1830) Membracis subulata was designated as type of the new genus Stictolobus by Metcalf (1916), who chose the new generic name to convey a similarity to species of the genera Stictocephala Stål and Cyrtolobus Goding ( Funkhouser 1951) . Funkhouser’s (1915) new species, Stictocephala minuta , was synonymized with Say’s (1830) subulata by Caldwell (1949). Funkhouser (1951), in fascicle 208 of Genera Insectorum, could not have been aware of Caldwell’s (1949) synonymy. The fascicle, although written before World War II, was not published until 1951 ( Evenhuis 1994). Genera Insectorum suspended operations in 1940 and resumed publication well after the war ended ( Moon 1985).

Metcalf and Wade (1965) apparently were unaware that Say’s (1830) Membracis subulata is preoccupied by Membracis subulata Weber, 1801 . In their catalog, they listed Say’s subulata as a junior synonym of Stictolobus minutus Funkhouser , and placed Weber’s (1801) subulata as a valid species of Membracis , without noting that Say’s species was a junior primary homonym. Kopp and Yonke (1979) alluded to Weber’s (1801) description of Membracis subulatus , rendering Say’s Membracis subulata a homonym, but they were inaccurate in referring to Stictocephala minuta Funkhouser, 1915 as a new name. With recognition of Say’s (1830) name as a junior primary homonym, Funkhouser’s (1915) minuta , although synonymized with Say’s subulata , became a valid name under Article 60.2 of the International Code on Zoological Nomenclature ( ICZN 1999). Accordingly, authorities regard Stictolobus minutus Funkhouser as valid (Metcalf and Wade 1965, Kopp and Yonke 1979, McKamey 1998, Deitz and Wallace 2012). A complete list of synonymy is available in catalogs by Funkhouser (1927), Metcalf and Wade (1965), and McKamey (1998).

Diagnosis.—Distinguished from superficially similar adults of ceresine membracids by overall shape, markings, and coloration of densely punctate pronotum ( Figs. 3, 4 ), combined with distinctive male genitalia: long, thin, curved lateral tooth and aedeagus with anterior arm absent and posterior arm with anteriorly facing hook near apex ( Fig. 5 ). Nymphs ( Figs. 6–10 ) identifiable by number, arrangement, and shape ( Funkhouser 1923) of dorsal spinelike scoli, and associated stalked chalazae, on head, pronotum, and abdomen.

Description.—Adults are slender with virtually no suprahumeral horns. In lateral view, the markings consist of two white to yellowish thin lines, each starting just behind the humeral angle of the pronotum, converging, and ending approximately one-third to one-half the length from the apex. Markings are obscure in some specimens. Coloration ranges from testaceous yellow to light or dark green in live specimens and straw yellow to dark green in preserved specimens.

Measurements are based on specimens from our study: males n = 8, females n = 10. Length (including wings): male 5.0– 5.6 mm, female 6.4–7.0 mm. Length of pronotum: male 4.5–5.2 mm, female 5.0– 5.6 mm. Width across humeral angles: male 2.2–2.3 mm, female 2.3–2.5 mm. Height of pronotum at humeral angle: male 1.2–1.4 mm, female 1.2–1.5 mm.

Distribution.— Say (1830) described Membracis subulata based on a specimen(s) from “ Maryland.” Funkhouser’s (1915) description of the new species Stictocephala minuta (a synonym of Say’s species) was based on a male he collected at Spring Creek, Georgia, which potentially could refer to multiple localities in the state (Georgia Atlas & Gazetteer, 1st ed., DeLorme ®, Yarmouth, Maine). Funkhouser (1915) collected the type specimen on 22 July 1912, soon after participating in the Cornell University Expedition to Okefenokee Swamp in southeastern Georgia from 28 May to 13 July 1912 (Wright and Harper 1913). He apparently continued to do fieldwork, rather than return to Ithaca, New York, and collected in southwestern Georgia at “Spring Creek.” Cornell entomologist J. Chester Bradley, who headed the Okefenokee Expedition ( Cornell University 1912), began to collect insects at Spring Creek in Decatur County while he was an assistant (1909–1911, 1913) to the State Entomologist of Georgia ( Wheeler 1913, Rehn and Hebard 1916, Calvert 1921, Pechuman 1975). The Decatur County Spring Creek, which we determine to be Funkhouser’s (1915) type locality, currently is the small town known as Brinson; it was founded in 1907 as the Mount Zion community, but the post office was called Spring Creek ( Krakow 1975).

Van Duzee’s (1890) comment that Say’s subulata was “unknown” to present-day entomologists was followed by its designation as a “lost” species ( Goding (1894). Metcalf (1916) rediscovered this “rare and interesting” membracid when he collected a male at light in Raleigh, North Carolina. He suggested that Say’s (1830) species had not been seen since its original description. Two putative Canadian records, however, preceded Metcalf’s (1916) paper: Hull, Quebec ( Provancher 1890; as Ceresa subulata Say ) and Ottawa, Ontario ( Harrington 1892; as Ceresa subulata, Say ?). Hull (now a district in the city of Gatineau) and Ottawa are on opposite sides of the Ottawa River. Records of the membracid from both provinces were included in catalogs by Funkhouser (1927) and Metcalf and Wade (1965), and were listed by Deitz and Wallace (2012). Canadian records of S. minutus were not included in the known distribution (southern U.S. only) listed by Funkhouser (1951) or in the checklist of Canadian and Alaskan Hemiptera ( Maw et al. 2000) . The latter publication, however, included Ontario and Quebec as the sole Canadian records for Stictocephala lutea (Walker) , an abundant ceresine occasionally observed “in swarms” ( Osborn 1911). It lacks pronotal (suprahumeral) horns or projections and is similar enough in coloration and size (6.5 mm long; Funkhouser 1917) to have been misidentified as S. minutus (5.0–7.0 mm). Metcalf (1916) was justified in saying that Say’s (1830) species had not been seen since the original description; he could not have known that Funkhouser’s (1915) new species, Stictocephala minuta from Georgia, eventually would be synonymized with Say’s subulata .

Stictolobus minutus , in addition to Georgia, Maryland, and North Carolina, now is known from Florida, Illinois, Mississippi, Texas, and Virginia (Kopp and Yonke 1973b, Deitz and Wallace 2012, Rothschild 2012). Specimens from these states (except Texas and Florida) are in the USNM and are represented by singletons at each locality: IL: Karnak, 26 Jul 1930, Knight & Rose (abdomen missing). MS: Aberdeen, 25 Jul 1921, C. J. Drake, ♀; Belmont, 5 Jul 1921, Ơ; Pascagoula , 12 Jul 1920, H. L. Dozier, ♀ (a ♀, with same data, is in FSCA); Tishomingo, 7 Jul 1921, C. J. Drake, Ơ. NC: [Pender Co.], Burgaw, 17 Aug 1926, Z. P. Metcalf, ♀. VA: “Jas.T.” [ Jamestown ?], 26 Jul 1925, E. D. Ball Collection, ♀.

We were unable to document a depository for a Texas specimen(s); V. Belov (pers. comm., 2019) could not find specimens in the Texas A&M University Insect Collection. The FSCA contains specimens from Florida: Alachua Co., Gainesville, Doyle Conner Bldg., 25 June 1973, F. W. Mead, blacklight trap, Ơ & 25–27 July, F. W. Mead, blacklight trap, ♀; Gainesville, 9 mi. NW, 3 Jul 1978, Robert A. Belmont, blacklight trap, ♀. Baker Co., Osceola NF, East Forest Tower, 2 Jun 1977, J. R. Wiley, blacklight trap, ♀. An additional collection from a previously known Mississippi locale is Belmont, 7 Jun 1921, H. L. Dozier, ♀; a new Mississippi locale is Jackson Co., Moss Point, Cumbest’s Saw Mill, 26 Jun 1968, L. H. Williams, blacklight trap, 2Ơ (FSCA). Data for Louisiana and South Carolina, posted on the iDigBio website (https:// www.idigbio.org/portal/records/cd47cd84- 4060-4e77-8eea-bd9454e1d477 and idigibio. org/portal/records/4b1d9c58-a711-480f- 9f2c-a2bb2e7c82cd), are here formally published as new state records: LA: Natchitoches Parish, Kisatchi National Forest, Red Bluff Campground, 13 Sep 2002, S. T. Dash, mercury vapor light, ♀ (UDEL); SC: Charleston Co., McClellanville, G. Stowe Duckery, 27 Jun 1970, L. L. Deitz, 2Ơ (NCSU). The iDigBio site also lists additional North Carolina collections: Pender Co., Burgaw, Big Savannah [no date or collector], Ơ, 3♀; Wake Co., Raleigh, 5 Jul 1905, Z. P. Metcalf, ♀ (NCSU). The Raleigh specimen apparently is the female Metcalf (1916) collected in Raleigh in early July (no year noted) and used to redescribe Say’s subulata .

We collected S. minutus only in Buck Creek’s West Barrens in Clay County, North Carolina. An attempt to collect it in the East Barrens (and in other southeastern locales) was unsuccessful.

Plant associations.— Metcalf (1916) speculated that the specimen of S. minutus (as S. subulata ) taken at light in Raleigh, North Carolina, came from oak [ Quercus ]. A putative “host,” bald cypress ( Taxodium distichum [L.] Rich.; Cupressaceae ), was mentioned without attribution (Kopp and Yonke 1973b). The source of their record is a specimen from Karnak, Illinois (USNM; D. D. Kopp, pers. comm., 2017), taken by “Knight and Rose” on Taxodium distichum .

We collected nymphs and adults of S. minutus from the basal stems and crowns of big bluestem ( A. gerardii ) from 2016 to 2019 and once from leaf litter within crowns. Nymphs were solitary, although occasionally two or three were collected from a large plant; they were not attended by ants, as is typical of North American ceresine treehoppers ( Funkhouser 1917: 399). On little bluestem ( S. scoparium ), fourth and fifth instars (n = 9) and two adults were collected in 2018, and one each of instars III to V was taken in 2019. In late July 2016, two fifth instars were beaten from a panicgrass ( Dichanthelium dichotomum (L.) Gould. The treehopper typically was found on its hosts near wooded areas of the powerline cut rather than on grasses in open areas devoid of trees and shrubs. Nymphs were not found at Buck Creek in sampling forbs or other grasses (e.g., Deschampsia cespitosa ), and they were not observed on big bluestem at nonserpentine sites in North Carolina and South Carolina. We did not observe nymphs or adults on woody plants.

Seasonality.—Only adults of S. minutus have previously been reported. The earliest records are 2 June in Florida (FSCA), 5 June in North Carolina (NCSU), 26 June in Mississippi (FSCA), and 27 June in South Carolina (NCSU). The latest records are 13 September in Louisiana (UDCC) and 17 August in Burgaw, North Carolina (USNM).

When S. minutus was discovered at Buck Creek on 10 July 2016, late instars (IV, V) and an adult (which escaped) were present. Fourth and fifth instars and adults were present on 23 July (3Ơ, 2♀) and 30 July (1Ơ, 2♀), and two fifth instars were found with three adults on 6 August. In 2017, nymphs were not detected in sampling big bluestem on 27 May or 8 June, but on 21 June, third and fourth instars were present. More fourth than third instars were found on 10 July, fifth instars and adults (2Ơ, 4♀) were present on 26 July, and one fifth instar (no adults) was observed on 12 August. The fifth instar collected live on 12 August, which is our latest record of a nymph, molted to an adult female four days later. Weekly sampling in 2018 indicated that S. minutus overwinters as eggs. Nymphs were not found on 28 April when new growth of big bluestem was about 5 cm high, or on 12 May when stem height was 11–15 cm. The first nymphs—one first and one second instar —were observed on 9 June (95 min of sampling). Eight nymphs were found on 16 June (1–I, 5–II, 1–III); 18 on 23 June (3–II, 15–III); 22 on 30 June (1–II [molted to III next day], 16–III, 5–IV); 21 on 8 July (5–III, 16–IV); 21 on 14 July (2–III, 16–IV, 3–V); 17 on 21 July (13–IV, 4–V); 9 on 28 July (3–IV, 6–V); and 8 on 4 August (3–IV, 5–V).

In 2019, a first instar was found on 1 June, our earliest nymphal record. Nine nymphs were observed on 15 June (5–II, 4–III); 7 on 22 June (1–II, 5–III, 1–IV); 14 on 6 July (7–III, 7–IV); and 3 on 4 August (3–V). An adult female was observed on 4 August, and one of the fifth instars taken that day molted to an adult female on 13 August. No individuals were found on 17 August.

In all four years, we observed fewer adults than nymphs. The earliest we found an adult (Ơ) was 8 July during weekly sampling in 2018, six weeks after the detection of a first and a second instar (9 June). A teneral male was observed that year on 14 July, two males on 21 July, the first female on 28 July, and one female on 4 August. In 2019, one adult (♀) was found on 4 August. The largest number of adults taken in a day’s sampling was six (2Ơ, 4♀) on 26 June 2017. Laboratory studies.—The first instar placed on big bluestem on 1 June was observed the next day, head up, on a stem about 4 cm from the base. After being found in the same position the next morning, the nymph was not seen again and no carcass was found. One of the two second instars placed on the same plant on 15 June was found the next day with its head up about 7 cm from the base; it apparently had molted. Later in the day, the now third instar was higher on the stem (15 cm from base) with its head up; it later moved down (ca. 2 cm), with its head facing the plant’s base. On the second day, the second instar was detected on a shorter stem, its head down, about 2.5 cm from the base. Neither nymph was found after 17 June.

Water droplets deposited on nymphs ran off the cuticular surface without beading on scoli, indicating that these spinelike structures are not hydrophilic. Submerged nymphs showed no air bubbles.

Figures

Figs. 3–10. Stictolobus minutus. 3, Adult male. 4, Adult female. 5, Male genitalia. 6, First instar. 7, Second instar. 8, Third instar. 9, Fourth instar. 10, Fifth instar.