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Research Article
The immatures of the New World treehopper tribes Acutalini Fowler and Micrutalini Haupt (Hemiptera, Membracidae, Smiliinae)
expand article infoStuart H. McKamey‡, Adam M. Wallner§
‡ c/o National Museum of Natural History, Washington, United States of America
§ USDA-APHIS-PPQ Plant Inspection Station, Linden, United States of America

Corresponding author: Stuart H. McKamey ( stuart.mckamey@usda.gov )

Academic editor: Christopher H. Dietrich
© 2022 Stuart H. McKamey, Adam M. Wallner.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation: McKamey SH, Wallner AM (2022) The immatures of the New World treehopper tribes Acutalini Fowler and Micrutalini Haupt (Hemiptera, Membracidae, Smiliinae). ZooKeys 1136: 187-208. https://doi.org/10.3897/zookeys.1136.90525
ZooBank: urn:lsid:zoobank.org:pub:91BEB5B2-E721-4125-BBA4-813ADDDB9C71
Open Access

Abstract

The nymphs of Acutalis Fairmaire, Bordoniana Sakakibara, Thrasymedes Kirkaldy, and Micrutalis Fowler are described and illustrated (Bordoniana and Thrasymedes for the first time). The nymphs of all four genera are exceedingly cryptic. The nymphs of some species lack scoli on the head and pronotum but all have paired scoli on the meso- and metathoracic nota and abdominal segments III–IX. Some species also have lateral rows of enlarged chalazae on the abdomen, and even large scoli ventrolaterally—the latter condition is unique within Smiliinae. The eggs are deposited in stems (not in exposed masses) and nymphs are solitary and not ant-attended. The fifth instar nymphs of Micrutalini range in length from 3.0–3.5 mm, much smaller than the fifth instars of most other treehoppers.

Keywords

Acutalis, Bordoniana, immature stage, life history, Micrutalis, Thrasymedes

Introduction

Adult treehoppers (Membracidae, Aetalionidae, and Melizoderidae) are well known for their expanded pronotum present in adults of more than 430 genera and 3,350 species (McKamey 1998 and recent additions). But in immatures, the pronotum is diminutive and accompanied by other structures, such as various arrangements of large spine-like structures (scoli) on the head and sometimes on the thoracic and abdominal segments, and enlarged setae with stalked or swollen bases (chalazae). We hypothesize that differences between adult and immature morphology may have evolved independently. Despite this wealth of potential diagnostic and systematically informative nymphal features, there have been few thorough descriptions of New World genera.

Besides the uniqueness of morphology of membracid nymphs, they also differ from nymphs of all other Auchenorrhyncha families in having the last visible abdominal segment (IX) fused ventrally, forming a tube containing the anal segments, which can be everted by the nymphs at will (McKamey and Brodbeck 2013). Behaviorally, membracid nymphs differ from those of most Auchenorrhyncha in being unable to jump (SHM pers. obs.).

The present paper is part of the larger effort to describe the immature stages of New World treehopper genera, which has so far covered the Caribbean genera Antillotolania Ramos, Deiroderes Ramos (McKamey and Brodbeck 2013), and tribe Quadrinareini (McKamey and Wallner 2022). The nymphs of the continental tribes Amastrini (McKamey et al. 2015) and Thuridini (McKamey and Porter 2016), and the membracine genus Eunusa Fonseca (McKamey 1992) have also been described. This work treats two more tribes of the New World subfamily Smiliinae: Acutalini and Micrutalini. The nymphs of all four genera described here are exceedingly cryptic (Figs 4–7, 42, 43). Both tribes occur throughout much of North and South America and the West Indies (McKamey 1998). The two tribes are grouped in this paper because of their small size and similar features in their nymphs and their adults. Adults of both tribes are commonly collected because they are often conspicuous with their black markings on the pronotum or wing veins (e.g., Figs 41, 43). In contrast, the nymphs of these tribes are rarely observed or collected.

Despite the scarcity of Acutalini and Micrutalini nymphs in collections, and their solitary nature and cryptic coloration and morphology, there has been some progress in nymphal descriptions. Quisenberry et al. (1978) illustrated and described, through a key, fifth instars of most genera of Membracidae present in Missouri, USA, including Acutalis and Micrutalis. They separated Micrutalis and Acutalis from other membracid genera based on the following features shared by both: paired median dorsal spines present on the abdomen but not on the head or pronotum, prothoracic tibia not dilated, anterior horn absent, and the outline of pronotum more or less rounded anteriorly. Acutalis was distinguished from Micrutalis based on a serrated dorsomedial line of the pronotum in Acutalis versus a smoothly rounded dorsomedial line of the pronotum and acute spines in Micrutalis. Tsai and Kopp (1981) described the life history, morphology, and phenology of Acutalis tartarea (Say), illustrating the adults, eggs, and all instars. They reported that eggs were laid in clusters of 12–15 eggs each, inserted into the epidermal tissues of the host plant, with about 1/3 of the egg exposed, usually into the axis area of a leaf. They also reported that the nymphs were gregarious near the terminal portion of the plant of two Asteraceae: ragweed (Ambrosia artemisiifolia L.) and China aster (Callistephus chinensis [L.] Nees, Asteraceae).

Deitz (1975) included three genera in Acutalini: Acutalis Fairmaire, Euritea Stål, and Thrasymedes. Generic additions since then include Bordoniana and Cornutalis (Sakakibara 1998, 1999a). Of these Acutalini genera, only nymphs of Acutalis have been described before now. The only host record for the genus Cornutalis is Baccharis sp., Asteraceae (Flórez-V. 2017).

Micrutalini only contains two genera: Micrutalis Fowler and Trachytalis Fowler. Several authors have contributed to our knowledge of micrutaline taxonomy and biology. For instance, Donald (1945) reported that Micrutalis sp. adults were “found in small numbers on Cordia macrostachya (Jacq.) R. & S.” (Boraginaceae) in Trinidad. In the present study, nymphs and adults of two Micrutalis species were also collected on Cordia, one in Ecuador and another in Nicaragua (see Material examined under Micrutalis). Sakakibara (1976) described two new species, Deitz (1983) referred one species to Rhexia Stål, and Sakakibara (1999b) provided a synopsis of Micrutalis, including 42 species. Nixon and Thompson (1987) described and illustrated nymphs of M. calva (Say) and listed many hosts, listed below. Amaro (2009) reported M. calva on Leucaena leucocephala (Lam.) de Wit (Fabaceae) in Cuba. Tsai and Brown (1991) provided a photograph of an M. malleifera Fowler nymph in a summary of pseudo-curly top virus in tomato (Lycopersicon esculentum Mill., Solanaceae). Flynn and Wheeler (2016) observed (but did not describe) nymphs of Micrutalis; they recorded adults of M. pallens Fowler on Anisacanthus thurberi [Torr.] A. Gray (Acanthaceae) but could not identify the observed nymphs because they were not reared to adults and there appeared to be two species on the host. Recently, however, Wheeler and Flynn (2021) described the nymphs of M. discalis (Walker) on mistletoe (Viscaceae), in general accordance with characters used in the aforementioned nymphal descriptions in this series.

In the present study, additional natural history information in provided as well as the descriptions of four genera of Acutalini and Micrutalini, two tribes of the New World subfamily Smiliinae. Nymphs of Bordonia and Thrasymedes have never been illustrated or described until now.

Materials and methods

Preserved specimens were either collected by the first author or found in the U.S. National Collection. Vouchers of all examined nymphs and their associated adults are deposited in the National Museum of Natural History, Smithsonian Institution, in Washington DC (USNM). They were collected in Ecuador, Mexico, Nicaragua, Peru, the United States, and Venezuela.

Photographs of dried specimens were taken with a Canon 5Dsr camera with an adjustable 65mm lens. Photos were taken using Capture One Pro v. 10.1.2, 64 bit, build 10.1.2.23 imaging software, aided by CamLift v. 2.9.7.1. The specimen was illuminated using two adjustable Dynalite MH2050 RoadMax flash heads, each attached to a Manfrotto 244 arm. The light was diffused using a simple, lampshade-style cone of translucent paper between the specimen and light sources. After individual “slices” were photographed, they were compiled into a single, composite image using Zerene Stacker - USDA SI-SEL Lab Bk imaging system, v. 1.04, build T201706041920. Stacked images were enhanced and edited in Adobe Photoshop CSS Extended v. 12.0.

Results

Key tzo 5th instars of Acutalini genera (excluding Euritea and Cornutalis) and Micrutalis. Fifth instars differ from earlier instars in having a well-developed forewing pad that attains the posterior margin of the first visible abdominal segment (segment III) and usually overlaps part of the second visible segment (segment IV).

1 Total length 3.5 mm or less Micrutalis
– Total length 4.3–8.5 mm 2
2 Abdomen laterally glabrous, not setose; dorsal scoli directed posteriorly (Figs 3–7) Acutalis
– Abdomen laterally densely setose (Figs 8, 12, 18); dorsal scoli directed dorsally or dorsoposteriorly 2
3 Abdominal tergum IX distinctly shorter than length of remaining abdominal segments combined (Figs 12, 13); abdominal terga IV–VIII with or without large scoli ventrolaterally (Fig. 14); head and prothorax with or without scoli Bordoniana
– Abdominal tergum IX as long as remaining abdominal segments combined (Fig. 18); abdominal terga IV–VIII without scoli ventrolaterally; head and prothorax with scoli Thrasymedes

Acutalini Fowler

Quisenberry et al. (1978) found features for distinguishing Acutalis, which is the only acutaline genus represented in Missouri, and those features were sufficient for that fauna. Considered within the larger context of Smiliinae, those features also apply to the Amastrini genera Bajulata Ball, Erosne Stål, Harmonides Kirkaldy, and some Amastris Stål (McKamey et al. 2015). But these features do not apply to the acutaline genus Bordoniana, which has abdominal scoli directed dorsally, nor the genus Thrasymedes, which has scoli on the head and pronotum, or even some other Acutalis, which have scoli on the head (1 pair) and pronotum (2 pairs) (Fig. 3). We also found that nymphs of Acutalini are solitary and not ant-attended, and we speculate that eggs are not laid in exposed masses but instead within host tissue. Tsai and Kopp’s (1981) report that the nymphs of Acutalis were gregarious near the terminal portion of ragweed host is interpreted here as a high population of solitary nymphs feeding at a preferred site with higher nitrogen. Nitrogen is recognized as an essential macronutrient for plant growth (Olas et al. 2019). Presumably, treehoppers feed on phloem, and plant nitrogen partitioning from source leaves to sinks occurs in the phloem (Tegeder and Masclaux-Daubresse 2017). Furthermore, Landrein et al. (2018) described a root-borne cytokinin signal that transduces nitrate availability to the shoot apical meristem within a matter of days and controls the stem cell population and, hence, meristem size and growth. In other words, meristems and young leaves have a higher concentration of nitrogen than other plant parts, and this may be why meristems are preferred feeding sites of many treehopper adults and nymphs.

Nymphs are unknown for the acutaline genera Cornutalis Sakakibara and Euritea Stål.

Acutalis Fairmaire

Figs 1–7

Nymph diagnosis

Body with full complement (9 pairs in total) of dorsal, short scoli from postmetopidium to last visible abdominal segment, and sometimes also 1 pair of scoli on head and 1 pair of scoli on premetopidium; metathoracic scoli directed forward, in opposite direction of abdominal scoli (backwards), low to tergal surface but not appressed; abdomen laterally with 3 rows of slightly enlarged chalazae but otherwise almost without setae.

Nymph description

Overall body. Fifth instar length 4.3 mm. Cross-section subtriangular; chalazae on thorax and abdomen, excluding those on scoli, sparse, almost absent; chalazal setae short; scoli parallel. Head. With simple conical scoli (except absent in Acutalis tartarea), directed anterad, length relative size to basal width about subequal; chalazal bases long-stalked; compound eye surface with setae; frontoclypeus with dense setae; enlarged chalazae absent between eyes, but present in front of ventral margin of eye and also adjacent to central or dorsal margin of eye; frons extending over central margin of eye. Prothorax. Premetopidium scoli present (except absent in Acutalis tartarea), directed anteriorly; postmetopidium scoli present, directed anteriorly; posterior extension of pronotum not surpassing anterior margin of metanotum; if present, premetopidial scoli length about 2–4× basal width; postmetopidial scoli length about 2–4× basal width. Mesothorax. Scoli bearing stalked chalazae; scoli directed dorsoanteriorly; forewing pad anterior costal margin straight; dorsal scoli length about 2–4× basal width; anterior basal side of scoli lacking cluster of enlarged chalazae; forewing pad surface chalazae absent; forewing pad costal chalazae present only only on base of costal margin; meso- and metathorax without lateral rows on enlarged chalazae. Metathorax. Scoli bearing stalked chalazae; scoli directed dorsoanteriorly; dorsal scoli length about 2–4× basal width. Legs. Chalazae of tibia on anterior and posterior lateral margins, absent or very few on dorsal surface; prothoracic tibia form subcylindrical. Abdomen. Terga III–VIII ventrolateral margins each with row of four or more enlarged chalazae; terga III–VIII dorsal scoli subequal in size to each other; terga III–VIII tallest dorsal scoli length 2–4× basal width; tergum IV dorsal scoli directed preapically dorsally, apically posteriorly but not appressed; terga III–VIII lateral rows bearing 3 rows slightly enlarged chalazae; lamellae absent; scoli bearing stalked chalazae. Segment IX: dorsal length subequal to combined length remaining visible abdominal terga; preapically with paired enlarged setae dorsally, with 1 pair dorsal scoli apically.

Figures 1–7. 

Acutalis 1–3 Acutalis fusconervosa Fairmaire from Chiapas, Mexico in anterior, dorsal, and lateral views, respectively 4 Acutalis sp. from Durham, NC, courtesy of Margarita Lankford 5 Acutalis sp. from Hoover, AL, courtesy of Vitaly Charny 6 Acutalis sp. from Costa Rica, ex Asteraceae, courtesy of Kenji Nishida 7 Acutalis tartarea, courtesy of Mark Rothschild.

Material examined

Acutalis fusconervosa, 1 adult, 2 nymphs, Mexico: Chiapas, 13 km S Pichucalco, 170 m alt., 17°26'38"N, 93°10'49"W, 2 November 2001, S.H. McKamey (USNM).

Note

There is a difference between Quisenberry et al.’s (1978) illustration of A. tartarea (Say) and the specimen of A. fusconervosa Fairmaire figured here (Fig. 7); the latter has a small pair of scoli on the pronotum, lacking in Quisenberry et al.’s illustration. This difference cannot be attributed to developmental changes because both are fifth instars deduced from wing pad size. Quisenberry et al.’s (1978) illustration was redrawn from Matausch (1912b).

Bordoniana Sakakibara

Figs 8–12, 13–17

Nymph diagnosis

Body densely setose; abdominal tergum IX distinctly shorter than length of remaining abdominal segments combined; abdominal terga IV–VIII sometimes with large scoli ventrolaterally; head and prothorax sometimes lacking scoli.

Nymph description

Overall body. Fifth instar length 5.1–6.5 mm. Cross-section subtriangular (except vertically depressed in Bordoniana sp. 2), chalazal dense on thorax and abdomen except scoli, obvious throughout body; chalazal setae long (expect short in Bordoniana sp. 1), scoli parallel (except splayed or divergent away from each other in B. virescens). Head. Scoli pair absent (except with simple conical scoli in B. virescens); scoli projection directed anterad in B. virescens; chalazal bases variable (see Remarks below); compound eye surface with setae; between eyes, enlarged chalazae variable (see Remarks below); scoli length about 2–4× basal width in B. virescens; enlarged chalazae present in front of ventral margin of eye and also adjacent to central or dorsal margin of eye (except enlarged chalazae absent in Bordoniana sp. 1.); enlarged chalazae adjacent to central or dorsal margin of eye present (except absent in Bordoniana sp. 1); frons extending over central margin of eye. Prothorax. Premetopidium scoli present (except absent in Bordoniana sp. 1); premetopidium scoli directed dorsoanteriorly; postmetopidium scoli absent; posterior extension of pronotum not surpassing anterior margin of metanotum but does not attain posterior margin (except surpasses posterior margin of metanotum in Bordoniana sp. 1); premetopidial scoli length relative to basal width variable (see Remarks below). Mesothorax. Scoli bearing tuberculate chalazae (except bearing stalked chalazae in B. virescens); scolar direction variable (see Remarks below); forewing pad anterior costal margin sinuate (except straight in B. virescens); forewing pad chalazae short and dense, continuously covered (except densely covered in long setae in Bordoniana sp. 1); scoli length about 2–4× basal width (except scoli about as tall as basal width in Bordoniana sp. 1); anterior basal side of scoli lacking cluster of enlarged chalazae (except present in B. virescens); forewing pad costal chalazae present along entire costal margin (except present only at base of costal margin B. virescens); lateral rows, if present, with most medial row extending onto meso- and metathorax (except not extending onto thorax in B. virescens). Metathorax. Scoli bearing tuberculate chalazae (except bearing stalked chalazae in B. virescens); scoli directed dorsally or almost so (except directed posteriorly in Bordoniana sp. 1); scoli length about 2–4× basal width (except scoli about as tall as basal width in Bordoniana sp. 1). Legs. Tibia with chalazae present on both lateral margins and dorsal surface; prothoracic tibia form subcylindrical (except foliaceus in Bordoniana sp. 1). Abdomen. Terga III–VIII ventrolateral margins variable (see Remarks below); terga III–VIII dorsal scoli subequal in length relative sizes to each other subequal (except scoli size decreasing posteriorly in B. virescens); terga III–VIII tallest dorsal scoli length about 2–4× basal width; tergum IV dorsal scoli directed preapically variable (see Remarks below); tergum IV dorsal scoli directed apically dorsoposteriorly (except posteriorly in Bordoniana sp. 1); terga III–VIII lateral rows bearing 2 rows enlarged chalazae (except not manifested in B. virescens); lamellae absent (except present with lateral margins converging, apex pointed in Bordoniana sp. 2); lamellae (if lamella present) bearing chalazae marginally and dorsally; scoli bearing tuberculate chalazae (except bearing stalked chalazae in B. virescens). Segment IX: dorsal length subequal to combined length of segments V–VIII (except subequal to combined lengths of segments VI–VIII in Bordoniana sp. 1); preapically with dorsal surface irregularly covered in chalazae.

Material examined

Bordoniana virescens Sakakibara, 1 adult, 1 nymph, Peru: Acobamba, July 1940, W.D. Funkhouser Collection (USNM); Bordoniana sp. 1, 1 adult, 1 nymph, Ecuador: Azuay, Baños, 2600 m alt., 23 May 1986, S.H. McKamey leg., lot# 05-23-23, 05-23-24 (USNM); Bordoniana sp. 2, 1 adult, 1 nymph, ECUADOR: Prov. Cañar. Ducur, via Cuenca-Guayaquil, 25-V-1986, ca 2520 m alt., S.H.McKamey leg., lot#86-0525-9, 86-0525-10 (USNM).

Remarks

Substantial morphological variation was found among the nymphs of the Bordoniana species examined. Specifically, the head and pronotum may have or lack scoli on the head and pronotum, and one species of undescribed Bordoniana has large scoli venrolaterally on segments IV–VIII (Fig. 14); this is unique in Smiliinae and rare among other membracid nymphs (e.g., present in Heteronotus Laporte [figured in Deitz and Wallace 2010]).

We also discovered differences among the three species of Bordoniana. Head: chalazal bases tuberculate in Bordoniana sp. 1, short-stalked in Bordoniana sp. 2, and long-stalked in B. virescens; enlarged chalazae between eyes absent in B. virescens, present as a single pair in Bordoniana sp. 2, and present as pair of vertical rows in Bordoniana sp. 1. Prothorax: premetopidial scoli length relative to basal width about subequal to their basal widths in Bordoniana sp. 2, about 2–4× their basal widths in B. virescens, and scoli absent in Bordoniana sp. 1. Mesothorax: scoli directed dorsoanteriorly in B. virescens, dorsally or almost so in Bordoniana sp. 2, and directed posteriorly in Bordoniana sp. 1. Abdomen: terga III–VIII ventrolateral margins each with a single enlarged chalazae in B. virescens, with acuminate lateral extensions in Bordoniana sp. 2 (Fig. 14), and with a row of four or more enlarged chalazae in Bordoniana sp. 1; tergum IV scoli directed preapically dorsally or almost so in B. virescens, dorsoposteriorly in Bordoniana sp. 2, and posteriorly but not appressed in Bordoniana sp. 1. The most striking difference, described above, is that Bordoniana sp. 2 bears ventrolateral scoli, identical in placement but different in form to certain Centrotinae, Heteronotinae, Stegaspidinae, and Procyrta Stål (Darninae) (SHM pers. observ.). No other smiliine nymphs have ventrolateral scoli.

Figures 8–12. 

Bordoniana 8, 9 B. virescens Sakakibara in lateral view, habitus and detail of head and portion of thorax, respectively 10–12 Bordoniana sp. 1 in anterior, dorsal, and lateral views, respectively.

Figures 13–17. 

Bordoniana sp. 2 13–17 nymph in lateral, dorsal, and anterior views, respectively 16 detail of head and portion of prothorax, lateral view 17 detail of abdominal segment IX (last visible segment), dorsal view.

Thrasymedes Kirkaldy

Figs 18–22

Nymph diagnosis

Body densely setose; with full complement of paired dorsal scoli from head to abdominal segment IX (12 pairs in total), though slender, not long and without stalked chalazae; abdominal segment IX as long as combined length of remaining abdominal terga; abdomen without scoli ventrolaterally.

Nymph description

Overall body. Fifth instar length 8.5 mm. Cross-section subtriangular; thorax and abdomen densely covered with chalazae, distinct throughout body; chalazal setae long; scoli parallel. Head. With simple conical scoli, directed anterad; chalazal bases long-stalked; compound eye surface with setae; enlarged chalazae between eyes present as pair of vertical rows; setae of frontoclypeus dense; scoli length about 5–7× basal width; enlarged chalazae in front of ventral margin of eye present; enlarged chalazae adjacent to central or dorsal margin of eye present; frons not extending over central margin of eye. Prothorax. Premetopidium scoli present, directed dorsoanteriorly; postmetopidium scoli present, directed anteriorly; posterior extension of pronotum surpasses anterior margin of metanotum, but does not attain1 its posterior margin; premetopidial scoli length about 5–7× basal width; postmetopidial scoli length about 5–7× basal width. Mesothorax. Dorsal scoli bearing stalked chalazae; scoli directed dorsoanteriorly and length about 5–7× basal width; anterior basal side of scoli lacking cluster of enlarged chalazae; forewing pad anterior costal margin straight; forewing pad surface densely covered by long chalazae; forewing pad costal chalazae along entire costal margin; lateral rows, if present, most medial row extending unto meso- and metathorax. Metathorax. Scoli bearing stalked chalazae; scoli directed dorsally or almost so; dorsal scoli length about 5–7× basal width. Legs. Chalazae of tibia present on both lateral margins and dorsal surface; prothoracic tibia form subcylindrical. Abdomen. Terga III–VIII ventrolateral margins each with 3 enlarged chalazae; terga III–VIII dorsal scoli length subequal to each other and bearing stalked chalazae; terga III–VIII tallest dorsal scoli length about 5–7× basal width; tergum IV dorsal scoli preapically directed dorsally or almost so, apically dorsoposteriorly; terga III–VIII bearing 1 lateral row of slightly enlarged chalazae; lamellae absent. Segment IX: longer than combined length of remaining abdominal terga, but shorter than length of rest of body; preapically with dorsal surface irregularly covered in chalazae.

Material examined

Thrasymedes pallescens (Stål): 39 adults, 1 nymph, 4 5th instar exuviae, Mexico: Michoacán, Route 150, km 270, 40 km E Panindicuaro, 2150 m elev., 19°52'55"N, 101°24'45"W, 9 November 2001, S.H. McKamey leg. (USNM).

Micrutalini Haupt

As for Acutalini, Quisenberry et al. (1978) gave distinguishing features for Micrutalis in Missouri, and those features were sufficient for that fauna. Their illustration, redrawn from Matausch (1912a), is consistent with a photograph of the live specimen (Fig. 23). The illustration by Nixon and Thompson (1987) shows the abdominal scoli more elevated than those in the specimen (Fig. 23) and also more than those in the illustration by Matausch (1912a).

Figures 18–22. 

Thrasymedes pallescens (Stål) 18–20 nymph in lateral, dorsal, and anterior views, respectively 21 detail of head and portion of prothorax, in lateral view 22 detail of abdominal segment IX (last visible segment), in dorsal view.

Considered within the larger context of Smiliinae, however, the features described by Quisenberry et al. (1978) and Nixon and Thompson (1987) are insufficient to distinguish them from the amastrine genera noted above (McKamey et al. 2015) and do not apply to all Neotropical Micrutalis species examined in our study. For example, Neotropical species of Micrutalis (except Micrutalis sp. 2) have scoli on all thoracic segments, not just the abdomen. Nymphs of Micrutalis are solitary and not ant-attended, and eggs are not laid in exposed masses.

In comparing morphology of adults and nymphs, we found more uniformity among Micrutalis adults than in their nymphs. Nymphs have yet to be discovered for Trachytalis Fowler, the only other micrutaline genus.

Micrutalis Fowler

Figs 23–28, 29, 30, 31–34, 35–37, 38–43

Nymph diagnosis

Fifth instar body length 3.0–3.5 mm; head and premetopidium lacking enlarged chalazae or scoli, postmetopidium with short scoli or enlarged chalazae; mesonotum to abdominal segment IX with small paired scoli; abdominal terga with 1 or 2 well-developed rows of enlarged chalazae or scoli; body densely setose, triangular in cross-section, not vertically compressed; abdomen lacking ventrolateral lamellae; wing pad costal margin linear or almost so; fused portion of abdominal segment IX directed posteriorly.

Nymph description

Overall body. Fifth instar length 3.0–3.5 mm. Cross-section subtriangular (except laterally compressed in M. dubia Fowler); chalazae on thorax and abdomen usually dense; chalazal setae long; no parts of body covered with wax-like substance; dorsal contour of abdomen in lateral view linear; scoli parallel; overall body in dorsal view elongate. Head. Lacking scoli; dorsal or anterior rounded protuberances absent; chalazal bases long-stalked (except tuberculate in M. dubia); chalazal setae simple, needlelike (except narrowly peltate in M. dubia) compound eye surface with setae; enlarged chalazae present or absent between eyes; setae of frontoclypeus scattered and sparse (except dense in M. callangensis); enlarged chalazae present in front of ventral margin of eye; enlarged chalazae present adjacent to central or dorsal margin of eye; frons extending over central margin of eye. Prothorax. Premetopidium lacking scoli; postmetopidium without dorsal paired structures or, if present (Fig. 33), with enlarged chalazae or small scoli directed dorsoposteriorly or dorsally then abruptly posteriorly; posterior extension of pronotum not surpassing anterior margin of metanotum, apex narrowly convex or acute; pronotal lateral margin rounded; postmetopidial scoli, if present, length about 2–4× basal width; metopidial sulcus not incised. Mesothorax. Dorsal structures consisting of paired scoli; scoli bearing stalked chalazae; scoli directed dorsoposteriorly or dorsally then abruptly posteriorly (except bluntly rounded in M. callangensis); forewing pad anterior costal margin form straight (except weakly sinuate in M. dubia); forewing pad surface chalazae sparse and with short setae (except densely covered in long setae in M. callangensis); scoli length about 2–4× basal width (except subequal to basal width in M. callangensis); anterior basal side of scoli lacking cluster of enlarged chalazae; forewing pad costal chalazae present only on base of costal margin (except along enture costal margin M. callangensis); lateral rows of abdomen with most medial row extending onto meso- and metathorax. Metathorax. Dorsal structures consisting of paired scoli; scoli bearing short-stalked chalazae; scoli directed dorsoposteriorly or dorsally then abruptly posteriorly; dorsal scoli length about 2–4× basal width (except subequal to basal width in M. callangensis). Legs. Tibia with chalazae present on both lateral margins and dorsal surface; prothoracic tibia form subcylindrical; metathoracic tarsal length subequal to pro- and mesothoracic tarsal length; all first tarsomeres distinctly shorter than second tarsomeres. Abdomen. Terga III–VIII ventrolateral margins lacking scoli but each with 2 enlarged chalazae (except with a single enlarged chalazae in M. callangensis); terga III–VIII with dorsal scoli present, subequal in size to each other (2–4× basal width). directed dorsoposteriorly or dorsally then abruptly posteriorly; terga III–VIII with lateral 1 or 2 rows of enlarged chalazae (Fig. 33) or manifested as scoli (in M. callangensis); abdominal scoli bearing stalked chalazae (except bearing tuberculate chalazae in M. dubia). Segment IX: distal half tubular in cross-section; dorsal length subequal to length of segment V–VIII (except subequal to combined length of remaining visible abdominal terga in M. callangensis); preapical dorsal surface irregularly covered with chalazae; dorsal structures at apex consisting of paired scoli; ventral extension subequal to dorsal extension; fused portion of segment IX directed posteriorly and distal to unfused portion; unfused portion distally not bifurcate.

Figures 23–28. 

Micrutalis nymphs 23 M. calva from Allison Park, Allegheny Co, PA, courtesy of John Rosenfeld 24 M. discalis (Walker) on mistletoe from AZ, courtesy of Al Wheeler 25 Micrutalis sp. from Costa Rica ex Miconia calvescens DC (Melastomataceae), courtesy of Kenji Nishida 26 Micrutalis sp. from León, Nicaragua, lateral view 27, 28 M. dubia Fowler, from Zona los Cinaros, Mérida State, Venezuela, in dorsal and lateral view, respectively.

Figures 29, 30. 

Micrutalis sp. 2 from Loja, Ecuador in lateral and dorsal view, respectively.

Figures 31–34. 

Micrutalis sp. 31 habitus anterior view 32 detail posterior abdomen in dorsal view 33, 34 habitus in lateral and dorsal views, respectively.

Figures 35–37. 

Micrutalis callangensis Goding in anterior, dorsal, and lateral views, respectively.

Figures 38–43. 

Micrutalis 38–40 Micrutalis sp. in anterior, detailed lateral head and portion of pronotum, and detailed abdomen, dorsal view, respectively 41, 42 Micrutalis undescribed sp., adult and nymph from Costa Rica, ex Hamelia patens Jacq. (Rubiaceae), courtesy of Kenji Nishida 43 Micrutalis undescribed sp., adult (upper right) and nymph (lower left, indicated by arrow) from San Juan, Bolivia by © Kozue Kawakami (CC BY).

Material examined

Micrutalis callangensis, 1 adult, 1 nymph, Ecuador: Cañar, Ducur, 25 May 1986, S.H. McKamey leg., lot # 86-0525-4, 86-0525-5 (USNM); Micrutalis undescribed species, 2 adults, 1 nymph, Nicaragua: Leon Finca N.I.L., 8 [October] 1989, J.M. Maes leg., ex Cordia sp. (USNM); M. dubia, 1 adult, 2 nymphs, Venezuela: Ed. Merida, Zona Los Cinaros, 58 km SW Merida, 24 July 1984, S.H. McKamey leg., lot #1008, 1009 (USNM). Micrutalis sp. 2, 2 adults, 2 nymphs, Ecuador: Loja, Loja, ca 2000 m alt., 30 May 1986, S.H. McKamey leg., lot #86-0530-7, 86-0530-8 (USNM); Micrutalis sp., 1 nymph (unassociated with adults), Mexico: Animal and Plant Health Inspection Service (APHIS) intercept APSCA191974874004 at San Ysidro, California, 15-VII-2019, ex Dysphania ambrosioides (L.) Mosyakin & Clemants (Amaranthaceae; commonly known as espazote, Mexican tea, paico, and wormseed).

Hosts

The great majority of Micrutalis species lack host information. Nevertheless, there are some host records in the literature and among specimens examined in this study. Nixon and Thompson (1987) reported that M. calva was polyphagous, with adults feeding on wormwood, soapwort, sycamore, redbud, ironweed, alfalfa, ragweed, sunflower, black locust, and honey locust. Nixon and Thompson (1987) also reported that nymphs have been collected on ironweed, ragweed, sunflower, and honey locust (Gleditsia triacanthos L.); nymphs were collected on ironwood, ragweed, sunflower, and honey locust. The holotype of M. henki Sakakibara (1999b) was collected on Luhea [sic, for Luehea] seemannii Triana & Planch. Flynn and Wheeler (2016) recorded M. pallens on Anisacanthus thurberi [Torr.] A. Gray, Acanthaceae, but could not identify the Micrutalis species because the nymphs were not reared to adults. Wheeler and Flynn (2021) recorded M. discalis (Walker) from mistletoe (Phoradendron californicum Nutt., Viscaceae). The M. dubia from Ecuador in our study was collected on Cordia sp., Boraginaceae. The APHIS intercepted nymph was on Dysphania ambrosioides (L.) Mosyakin & Clemants (Amaranthaceae).

Remarks

Although Micrutalini adults are distinguished by their wing venation and genitalia, the small size of the fifth instars of Micrutalis sets them apart from most treehoppers. The only New World treehoppers that rival their small size are some Bolbonota Amyot & Serville, Eunusa Fonseca, some Tragopini, Thuridini, Quadrinareini, some Amastris Stål, Centrodontini, Endoiastinae, Deiroderes, Brachytalis Metcalf & Bruner, Brachybelus Stål, and Abelus Stål. Micrutalis nymphs differ from the nymphs of all these small genera in one or more of the features listed above in the diagnosis of Micrutalis. In contrast to nymphs of Micrutalis, Bolbonota nymphs are covered with white wax-like exudate; Eunusa nymphs are covered with erect, stalked scoli and have the segment IX directed dorsally; nymphs of Tragopini, Thuridini, and Quadrinareini lack scoli entirely; Centrodontini and Endoiastinae lack setae, Brachytalis nymphs have the posterior margin of the metathorax mesally lengthened; and Deiroderes and Brachybelus nymphs have ventrolateally flattened abdominal lamellae. The only genus among these for which the nymphs are unknown is Abelus. We presume these resemble those of the closely related Ischnocentrus Stål, which have the costal margin of the wing pad notched. The most unusual Micrutalis species is M. callangensis, with its rounded meso- and metathoracic scoli, and its abdomen with lateral rows manifested as scoli rather than enlarged chalazae, and a proportionately longer segment IX.

Conclusions

Considering the great variability that we have observed, morphological variation within Acutalini and within Micrutalini are underestimated. This situation is exacerbated by the absence of known nymphs for Euritea and Cornutalis (Acutalini) and Trachytalis (Micrutalini). This is especially the case for Micrutalis, for which only a few of the many species are known. For all genera in Acutalini and Micrutalini, we expect that more species will reveal more variability than accounted for here. In this respect it is like any taxonomic revision; it represents only the species studied and becomes outdated when more are available for examination.

Acknowledgements

We thank Taina Litwak and Alyssa Seemann (USDA/ARS Systematic Entomology Laboratory) for taking and processing photographs, Alyssa Seemann for producing plates, Vitaly Charny, Margarita Lankford, Jean Michel Maes, Kenji Nishida, John Rosenfeld, Mark Rothschild, and Al Wheeler for photographs of live specimens, and L.L. Deitz (North Carolina State University) for comments on an earlier draft. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply endorsement by the USDA. The USDA is an equal opportunity provider and employer.

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