Trionymus okiensis, Tanaka, 2018

Tanaka, Hirotaka, 2018, Trionymus okiensis sp. nov., a new species of mealybug from Japan (Hemiptera: Coccomorpha: Pseudococcidae), Acta Entomologica Musei Nationalis Pragae 58 (1), pp. 31-34 : 33-34

Trionymus okiensis sp. nov.

( Fig. 1 )

Type material. HOLOTYPE: adult ♀, JAPAN: SHIMANE / PREFECTURE: Oki Islands, / Dougo Island, / Okinoshima-cho, / Kaminagu. 24.X.2014 // Host plant: Miscanthus / sinensis ANDERSSON / H. TANAKA coll. // Trionymus okiensis / Tanaka, 2018 / HOLOTYPE [red label]’ (mounted on a slide by itself, NSMT-I-Ho 00083. PARATYPES: 3 adult ♀♀, JAPAN: SHIMANE / PREFECTURE: Oki Islands, / Dougo Island, / Okinoshima-cho, / Kaminagu. 24.X.2014 // Host plant: Miscanthus / sinensis ANDERSSON / H. TANAKA coll. // Trionymus okiensis / Tanaka, 2018 / PARATYPE [blue label] (on three slides, 1 slide NSMT-I-Ho 00084, 2 slides in EUMJ).

Description. Adult female. Body elongate oval, 2.6 (2.5–3.0) mm long and 1.0 (1.0–1.1) mm wide, derm membranous; segmentation relatively well-developed. Anal lobes distinct but not prominent, dorsum of each lobe with a weakly sclerotized area and ventral surface with a long apical seta, 144–147 (133–166) μm long. Antenna 358–370 (326–370) μm long, with 7 or 8 segments and many flagellate setae; subapical segment with 1 fleshy seta and apical segment with 3 or 4 fleshy setae. Legs well-developed, with many flagellate setae; hind trochanter + femur 320–330 (300–330) μm long, hind tibia + tarsus 334 (313–340) μm long; claw 30 (30–33) μm long. Ratio of lengths of hind tibia + tarsus: trochanter + femur 1.0 (1.0–1.1); ratio of lengths of hind tibia to tarsus 2.1 (1.9–2.2). Paired tarsal digitules present, subequal in length and both minutely knobbed. Translucent pores few, present on hind coxa only. Labium about 77 (75–81) μm long, shorter than clypeus. Circulus present between 3 rd and 4 th ventral abdominal segments, 55 (50–55) μm long and 70 (62–74) μm wide, divided by intersegmental line. Ostioles present, each with inner edges of lips not sclerotized; anterior ostioles each with a total for both lips of 21–30 trilocular pores and 2–4 (0–4) setae; each posterior ostiole with a total of 10–11 (7–11) trilocular pores and 0 (0–1) setae for both lips. Anal ring 92 (80–92) μm wide, with 2–3 rows of cells, bearing 6 setae, each seta 145–155 (138–162) μm long. Cerarii numbering 5 (4–6) pairs, with 1 pair of frontal cerarii on head, other cerarii situated on posterior abdominal segments, but occasionally some cerarii lacking. Anal lobe cerarii situated on sclerotized cuticle, each containing 2 conical setae, each seta 26–29 (27–33) μm long and about 8–10 (8–14) μm wide at base; plus 18–19 (13–19) auxiliary setae and concentration of trilocular pores. Penultimate cerarii each containing 2 conical setae and a few auxiliary setae, situated on membranous cuticle. Cerarii situated further forward generally each with a pair of conical setae and a few auxiliary setae, or with 1 conical seta and with or without a few auxiliary setae.

Dorsum. Setae slender and flagellate, each 15–60 (13–60) μm long, longest setae present on posterior part of abdomen. Trilocular pores evenly distributed. Oral-collar tubular ducts of two sizes present: (i) large-type ducts, each about 3–4 μm in diameter, obviously wider than a trilocular pore, present in band across most abdominal segments, marginal area of head and thoracic segments, and medial area of thoracic segments; (ii) small-type ducts, each about 1.5–2 μm in diameter, relatively sparse on abdominal segments, intermixed with the larger type. Discoidal pores sparse, mostly situated on posterior segments. Multilocular disc pores each 7–9 μm wide, present on abdominal segments as follows: I 0 (0), II 1 (0–1), III 1 (0–1), IV 2 (1 or 2), V 6 (1–6), VI 10 (2–10), VII 2 (1–5), VIII 0 (0).

Venter. Ventral surface bearing slender flagellate setae, each 20–78 (20–86) μm long, longest on posterior part of abdomen and head. Multilocular disc pores, each 7–9 μm wide, mostly present on posterior abdominal segments, occasionally a few present on some segments of head, thorax and anterior abdomen. Trilocular pores evenly distributed. Oral-collar tubular ducts present in two sizes, same as on dorsum: large type ducts with diameter 3–4 μm (diameter slightly larger than that of a trilocular pore) present in irregular band on head, in transverse bands on all thoracic and abdominal segments, but mostly concentrated on abdominal segments; small-type ducts more sparsely distributed on most abdominal segments, intermixed with the larger type. Discoidal pores rarely present, mostly situated on posterior segments.

Differential diagnosis. The only other species of Trionymus so far known from Japan, T. kobotokensis Kanda, 1959 , can be relatively easily distinguished from T. okiensis sp. nov. using the identification key below.

Outside Japan, T. okiensis sp. nov. is quite similar to T. frontalis McKenzie, 1967 so far only known from California, USA ( GARCIA MORALES et al. 2017) in having a pair of frontal cerarii, oral-collar tubular ducts of two different sizes on the dorsal surface, and a circulus divided by an intersegmental line. However, the new species is distinguishable from T. frontalis by the following characters (characters of T. frontalis are given in parentheses): cerarii numbering 4–6 pairs (3 pairs); relatively deep oral-collar tubular ducts on dorsum present in two distinctly different sizes (different types of dorsal ducts are difficult to distinguish from each other, and the ducts are so shallow that outer ductules can be hardly seen in slide-mounted specimens); legs short, with hind trochanter + femur 300–330 μm long (legs relatively long, with hind trochanter + femur 420–458 μm long).

Trionymus okiensis sp. nov. is also similar to Dysmicoccus boninsis ( Kuwana, 1909) , the pantropical pest of sugarcane ( Saccharum officinarum L.), in having a pair of frontal cerarii and oral-collar tubular ducts of two different sizes on the dorsal surface. However, it differs from D. boninsis in the following characters (characters of D. boninsis are given in parentheses): more than 10 auxiliary setae on each anal lobe cerarius (fewer than 10); multilocular pores on the dorsum (without dorsal multilocular pores); circulus divided by an intersegmental line (circulus not divided); and narrow and parallel-sided body with the ratio of its maximum length to maximum width 2.5–2.7 (body usually relatively broad, with ratio of maximum body length to maximum body width 1.7–2.0).

Etymology. The new species is named after the archipelago where it was first collected (Dougo Island is one of the Oki Islands), combined with the Latin suffix“ -ensis ” indicating the place of origin, in order to form an adjective.

Comments on the classification. Some species of the genus Trionymus are very close to several species belonging to Dysmicoccus Ferris, 1950 and the current definitions of these genera are probably arbitrary ( WILLIAMS 2004). Most researchers follow MCKENZIE (1967), who placed species with 6 or more pairs of cerarii in Dysmicoccus , and species with 5 or fewer pairs of cerarii in Trionymus . However, on this basis it is difficult to determine the generic position of Dysmicoccus angustifrons ( Hall, 1926) , which possesses 2–6 (sometimes up to 10) pairs of cerarii (DANZIG & GAVRILOV- ZI- MIN 2015), resulting in some controversy about its placement (e.g., DANZIG & GAVRILOV- ZIMIN 2015, MATILE- FERRERO et al. 2015). A similar taxonomic problem probably occurs also in T. okiensis sp. nov. because it has 4–6 cerarii. In this study, T. okiensis is placed tentatively in Trionymus based on its morphological similarity to T. frontalis (i.e., having two types of oral-collar ducts on dorsum, a small number of multilocular pores on dorsum, a circulus divided by an intersegmental line, and cerarii fewer than 6 pairs).

Figures

Fig. 1. Trionymus okiensis sp. nov., left side dorsal view, right side ventral view. ALC – anal lobe cerarius; ANT – antenna; DP– discoidal pore; LG – hind tibia, tarsus and claw; MP – multilocular pore; OCD I – large type of oral-collar tubular duct; OCD II – small type of oral-collar tubular duct; PC– penultimate cerarius; TP – trilocular pore. Scale bars: 200 μm for ANT, LG; 100 μm for ALC, PC; 10 μm for others.