Plagiognathus marinoccidens, Introduction, 2023

Introduction, Tomohide Yasunaga, 2023, Two new thermophilic species of the plant bug genus Plagiognathus from Japan and Taiwan (Hemiptera: Heteroptera: Miridae), Bonn zoological Bulletin 72 (1), pp. 25-40 : 30-39

Plagiognathus marinoccidens sp. nov.

urn:lsid:zoobank.org:act:B0A83320-5C9E-41B5-9247-26B4424B4E60

Figs 1H–I , 2 A−D, 3A–K, 4, 5E−H, 6E–H, 7B, 9A−I

Diagnosis. Recognized by its small size; generally fuscous body ( Figs 2A–D , 3B ); uniformly darkened head; short antennal segment II; relatively long labium that is longer than metafemur; relatively narrow peritreme of scent efferent system ( Fig. 5G ); creamy yellow femora and tibiae; rather stout, blunt-tipped phallotheca ( Fig. 9B ); short, slender apical blades of vesica ( Fig. 6E– H , 9E–F ); and relatively narrow interramal sclerite ( Fig. 9H ) with densely distributed, comb-like microstructures ( Fig. 9I ), in addition to unique thermophilic habitat preference. This new species is assumed to be sister to P. amurensis , from which P. marinoccidens sp. nov. can be distinguished by the characters mentioned in the above key (couplet 4), smaller size, generally fuscous basic coloration ( Fig. 2A–D , vs 2H–I), slenderer vesical blades ( Fig. 9E , vs 9O), smaller sclerotized rings ( Fig. 9G , vs 9J), and more densely distributed microstructures on the narrower interramal sclerite ( Fig. 9H–I , vs 9K–L). Pal- er color variant ( Fig. 3C–D ) was confirmed in the 2 nd (autumn) generation females; however, only three of 43 specimens had the paler coloration, and extent of the pale grayish brown parts on the dorsum is rather restrict- ed ( Fig. 3C ), by comparison with P. amurensis ( Fig. 2I ).

Plagiognathus marinoccidens sp. nov. is also externally very similar to P. yomogi , but this Artemisia -inhabiting phyline is allopatric (known from colder climatic zones) and has the following different features: antennal segment III longer than head width across eyes; anterior margin of profemur usually with a dark stripe; metafemur with sparser dark spots ventrally ( Fig. 4 ); metathoracic scent efferent system triangular, with wider peritreme ( Fig. 5N ); phallotheca tapered and sharpened apically ( Fig. 8L ); vesical with thick primary blade ( Fig. 8N ); and inner half area of interramal sclerite smooth, lacking microstructures ( Fig. 8J ).

The nymphs ( Figs 3H–K ) of P. marinoccidens sp. nov. are recognized readily by the generally pale green coloration, annulated antennae and striped femora. The final instar nymph of the new species is very similar to that of P. amurensis ( Fig. 3M ); the former can be distinguished from the latter by the yellowish basic coloration, darkened apical ¼ of the antennal segment II and enlarged dark spots on the metatibia.

Etymology. From Latin, marinus (marine, of the sea) combined with occidens (west), referring to the restricted habitats of this new species along the westernmost coastal zone of Mainland Japan; an adjective.

Type material

Holotype. JAPAN – ♂ ( AMNH) ( AMNH _ PBI 00380759 ), Kyushu, Nagasaki Pref., Nagasaki City, Kabashima Island , 32°33′22.2″ N, 129°46′39.2″ E, on Humulus japonicus (sweep-netting young leaves and stems), 15 Jun. 2013, T. Yasunaga.

Paratypes. JAPAN – 1 ♂, 1 ♀ ( TYCN), same lo- cality data as for holotype • 1 ♂ ( TYCN), Nagasa- ki City, Kinkai-Tonehara (harbor), 32°54′04.1″ N, 129°47′42.1″ E, on Humulus japonicus (young leaves and stems), 2 Jun 2022 , T. Yasunaga • 1 ♀ ( TYCN), Nagasaki City, Kohno’ura-Ougiyama , 32°53′20.9″ N, 129°43′26.3″ E, UV lighting, 23 Jul. 2022 , T. Yasuna- ga • 32 ♂♂, 13 ♀♀ ( AMNH, NBIC, TYCN), Nagasa- ki City, Kohno’ura Harbor ( Fig. 3A ), 32°52′54.7″ N, 129°40′44.7″ E, on Humulus japonicus (inflorescenc- es and leaves), 1 Oct 2022 , T. Yasunaga • 8 ♂♂, 2 ♀♀ ( TYCN) (4 th or 5th instar nymphs when collected and reared with synthetic diet, then emerging on 3–5 Oct 2022) • 20 ♂♂, 22 ♀♀ ( CNC, NMNS, TYCN) same collection data as for preceding • same collection data as for preceding, 8 Oct. 2022 • 2 ♂♂, 7 ♀♀ (3 rd –5 th instar nymphs when collected and reared, then emerging on 9–13 Oct. 2022, and 1♂ dead on Oct. 21, 1 ♀ on Oct. 30, 1 ♂, 3 ♀♀ on Nov. 5 and 3 ♀♀ on Nov. 6) ( TYCN) • 17 ♂♂, 6 ♀♀ ( AMNH, TYCN), same collection data as for preceding, 12 Nov. 2022 • 1 ♂, 2 ♀♀ ( NBIC, TYCN), Nagasaki Pref., Saikai City, Seihi Town, Nagasaki Biopark (Zoo), 32°59′19″ N, 129°47′14″ E, UV lighting, 20 Jun. 2013 , T. Yasunaga.

Description

General shape not sexually dimorphic; female has slightly larger size, wider vertex and shorter antennal segment II ( Table 1) as in above new species; color variation not significant but body partly pale grayish brown in 2 nd (autumn) generation female as in Fig. 2A–D; 2 nd generation slightly larger than the 1 st ( Table 1). Body rather elongate, subparallel-sided, small-sized; basic coloration fuscous (pale variant rarely present in 2 nd generation female, with partly grayish brown head, pronotum, lateral margins of scutellum, posterior part of clavus and ventral posterior part of abdomen, cf. Fig. 3C–D ); dorsal surface widely shiny fuscous ( Fig. 2A–D ), with uniformly distributed, pale, simple setae, lacking silvery setae ( Figs 2A–D , 3C, G , 5D ). Head, including vertex and frons, shiny fuscous, with sparsely distributed, pale, upright setae. Antenna almost uniformly dark brown; male segment II about as long as basal width of pronotum; segment III and IV whitish in fresh specimens (e.g., Fig. 2B ); segment III as long as or shorter than head width across eyes. Labium shiny creamy yellow, longer than metafemur; its apex slightly surpassing apex of mesocoxa; apical half of segment IV dark reddish brown. Pronotum, mesoscutum and scutellum uniformly fuscous, shining; scutellum flat; thoracic pleura almost uniformly darkened ( Fig. 1H–I ); metathoracic scent efferent system dark brown, with small, narrow peritreme ( Fig. 5G ). Hemelytron uniformly shiny fuscous, except for basal margin and apex of cuneus pale; membrane smoky brown, with posteriorly whitish vein. All coxae creamy yellow, with more or less darkened bases; legs creamy yellow; each femur without noticeable dark stripe along anterior margin; pattern of ventral femoral spots as in Figs 1H–I , 4 ; metafemoral dark spots generally smaller than those of P. amurensis (cf. Figs 1F–G , 4 ); each tibia with a dark (knee) spot at joint with respective femur; apex of each tarsomere III darkened; pretarsal structure as in Fig. 5H ; claws rather slender and sharpened, with pulvilli somewhat widened towards apex. Abdomen almost entirely shiny fuscous in both sexes. Male genitalia ( Figs 6E–H , 9 A−F): Right paramere relatively wide, somewhat flattened ( Fig. 9A ); hypophysis of left paramere sub-triangular ( Fig. 9C ); phallotheca rather stout, blunt-tipped ( Fig. 9B ); vesica sigmoid but not coiled, with short, slender apical blades that are not thickened basally ( Figs 6E–H , 9E–F ). Female genitalia ( Figs 7B , 9G–I ): Sclerotized ring rather small, with thicker anterior margin ( Figs 7B , 9G ); posterior wall relatively narrow ( Fig 9H ); interramal sclerite (except for its smooth inner corner) with densely distributed, comb-like microstructures ( Fig. 9I ).

Measurements

See Table 1. Holotype male: Total body length 3.19; head width across eyes 0.68; vertex width (interocular space) 0.33; lengths of antennal segments I–IV 0.21, 0.95, 0.63 and 0.33; total length of labium 1.20: basal width of pronotum 0.99; maximum width across hemelytra 1.20; and lengths of metafemur 1.08, tibia 1.68 and tarsus 0.47, respectively.

Biology

The breeding host of this new bivoltine species was confirmed as a Japanese wild hop, Humulus japonicus . The immature forms of the 2 nd (autumn) generation were recently discovered ( Fig. 3A–H ), and the newly emerged adults of the 1 st generation (cf. Fig. 2B ) were collected from young leaves and stem vines of the host in early summer. The adults were occasionally attracted to UV light at night. Both of Plagiognathus marinoccidens sp. nov. and its assumed closest sibling, or P. amurensis , are associat- ed with the same plant species. However, the latter seems to have a univoltine life cycle, as both of the adults and nymphs of Japanese population were only found between late August to late October ( Yasunaga 2001; Yasunaga & Takai 2016), and the distributions of the two species are obviously disjunct from one another. Along coastal zones of Nagasaki Prefecture, the Japanese hop (often regard- ed as a rampant weed) grows everywhere. Nonetheless, the habitats of P. marinocciden are obviously restricted. Although I have carefully searched this bug at more than 20 sites for the past couple of years, only five collecting sites mentioned in the above type material section have hitherto yielded specimens. The adults of the second (autumn) generation occurring at Kohno’ura Harbor of Nagasaki City ( Fig. 3A , 32°52′54.7″ N, 129°40′44.7″ E) were observed to survive until early November when the host plant starts to wither.

Two new thermophilic species of the plant bug genus Plagiognathus from Japan and Taiwan 39 Schuh (2004) suggested that Plagiognathus species were associated with 39 vascular plant families and a number of members were arboreal including conifer-inhabitants. The Japanese species, except for P. pini Vinokurov , are known to feed on herbaceous weeds or climbers (see checklist above). So far as I am aware, predaceous food habit is yet to be reported for any Asian Plagiognathus species. However, both adults and immature forms of P. marinoccidens were recently observed to have positively preyed on an aphid, Phorodon japonensis Takahashi, 1965 ( Aphididae ) which often co-occurs with the plant bug on the Japanese hop, Humulus japonicus ( Fig. 3H ). In addition, the adults and every instar nymphs were successfully reared with a synthetic diet (diluted fermented milk beverage and dried brine shrimp eggs, Fig. 3E–F ), and all the immature forms developed into adults. The newly emerged females were observed to oviposit 3–4 days after eclosion ( Fig. 10A–B ) and to survive for 15–29 days (see the above type material section). When the adults were reared only with the pieces of the host plant, all were dead within a week and the females did not oviposit. Based on available evidences, this new phyline species appears more or less predaceous despite being a specialist of Humulus japonicus . Several reared adults were also observed to scavenge on fresh cadavers of small-sized dipteran flies ( Drosophila sp. , Megaselia sp. and Aedes albopictus as in Fig. 3K ). Two aphid species, Macrosyphoniella sanborni (Gillette) (original host: Chrysanthemum × morifolium of Asteraceae ) and an undetermined aphid from Quercus dentata ( Fagaceae ), were also preyed upon by the adults of the mirid in laboratory tests. Carnivorous food habit is assumed to be essential for propagation of P. marinoccidens .

Details of oviposition behavior were documented for relatively few mirid bugs ( Wheeler 2001). The present work confirmed that the eggs of Plagiognathus marinoccidens sp. nov. were deposited into the stem-vines of the host plant ( Fig. 10D ). The opercula were found to be wholly concealed by brownish pasty coats that at first sight seem simply the excrement ( Fig. 10C ). It was not until I was aware of the opercular seal that I could accurately locate the cryptically deposited eggs. However, it is currently not certain which organ (mouth, ovipositor or anus) secretes the brown matter during oviposition. The coating is considered significant for the eggs to survive for more than 7 months, since the aerial parts, or annual vines of the perennial host plant wither up in winter.

Acknowledgements. Special thanks are due to the following individuals or institutions for offering valuable specimens, useful information and/or supporting the author’s fieldwork: the late Dr S. Miyamoto (Fukuoka, Japan) ; the late Dr I. M. Kerzhner ( Zoological Institute , Russian Academy of Sciences , St. Petersburg); the late Mr S. Gotoh (Tanebe, Wakayama, Japan) ; the late Mr. S. Sakurai (Niigata, Japan) ; Prof. S. H. Lee and Mr. M. Oh (Seoul National University , Korea) ; Dr R. T. Schuh (Curator Emeritus, AMNH); Dr K. Nagai (Okayama, Japan) ; Dr K. Takahashi (Tsukuba, Japan) ; Mr M. Takai (Kochi, Japan) ; Dr R. K. Duwal ( CNC); Dr J. F. Tsai ( NMNS); Mr K. Watanabe (Yamagata, Japan) ; Mr M. Nozawa (Saitama, Japan) ; Mr M. Itoh (Director, NBIC); and Mr K. Tanaka and Mr G. Fukagawa (Nagasaki, Japan) . Mr M. Takai kindly provided some images of live bugs ( Fig. 2H–I ). I am also much indebted to Mr D. Terada ( CSR Division , Hitachi High-Tech, Tokyo, Japan) for generously allowing to use a tabletop scanning electron microscope. Thanks are extended to two anonymous reviewers and editors for reviewing the manuscript.

Figures

Fig 10. Plagiognathus marinoccidens sp. nov. A–B. Oviposition behavior. C. Brownish pasty coats sealing opercula D. Eggs de- posited into stem-vine of the Japanese hop.

Fig. 1.Dorsal (A–B, D, J) and left lateral (C, E−I, K−L) habitus images of Plagiognathus spp.A. P. chengshingi sp. nov., holotype, ♂. B−C. P. chengshingi sp. nov., paratype, ♂. D−E. P. chengshingi sp. nov., paratype, ♀. F. P. amurensisfrom Kume Town, Okayama, Japan. G. P. amurensis from Taebaek, Kangwon-do, Korea. H. P. marinoccidens sp. nov., holotype, ♂. I. P. marinoccidens sp. nov.,paratype, ♀. J. P. yomogi, ♂ from Hokkaido, Japan. K. P. yomogi, ♀ from Hokkaido. L. P. yomogi, pale variant ♀ from Yamagata, Japan.

Fig. 2. Habitus images of living individuals of Japanese Plagiognathus spp. A−B. P. marinoccidens sp. nov., ♂. C−D..P. marinoccidens sp. nov., ♀. D. P. marinoccidens sp. nov., ♀. E. P. chrysanthemi, ♀. F. P. collaris, ♂. G. P. collaris, ♂, pale variant. H. P. yomogi, ♂. I. P. yomogi, ♀. J. P. yomogi, ♂. K. P. pini, ♂. H–I. Courtesy of M. Takai.

Fig. 3. Habitat and habitus images of living individuals ofPlagiognathus marinoccidens sp. nov. (B–K, the 2nd generation collected at Fig. A, with reared samples, F–K) and P. amurensis (L–M, from Suwon, Korea). A. Vegetation of Humulus japonicus at sandy beach in Nagasaki, Japan, habitat of P. marinoccidens sp. nov. B. Adults on the breeding host. C. Paler variant ♀. D. Same, scavenging on cadaver of a mosquito, Aedes albopictus. E. Rearing kit with pieces of the host plant and synthetic diet. F. Adults and 5th instar nymph (left) feeding on synthetic diet. G. A female preying on an aphid. H. First instar nymph. I. Third instar.J. Final instar. K. Unpigmented adult ♂, just completing eclosion. L. Adult ♂, with orange-brown dorsum. M. Final instar nymph.

Fig. 5. A–D. Scanning electron micrographs for Plagiognathus chengshingi sp. nov. E–H. P. marinoccidens sp. nov. I–L. P. amurensis. M–O. P. yomogi. A, E, I, M. Left lateral habitus. B, F, J, N. Thoracic pleura, left lateral view. C, G, K. Metathoracic scent efferent system. Ventral habitus. D, H, L, O. Pretarsal structure of metaleg.

Fig. 9. A−F, M−O. Scanning electron micrographs of ♂ genitalia. G–L. Scanning electron micrographs of ♀ genitalia. A–I. Plagiognathus marinoccidens sp. nov. J–O. P. amurensis. A, M–N. Genital segment (pygophore) with phallotheca and parameres, dorsal view.B. Phallotheca. C. Left paramere. D−F, O. Vesica.G, J. Genital chamber, dorsal view. H−I, K−L. Posterior wall (I, L for structure of IRS in high magnification).Abbreviations: see Material and methods.

Fig. 6. A–D. Male genitalia (vesica) of Plagiognathus amurensis from Suwon, Korea. E–H. P. marinoccidens sp. nov. from Nagasaki, Japan. Abbreviations: see Material and methods.

Fig. 4. Metafemoral ventral dark spot pattern of six Japanese Plagiognathus spp.

Fig. 8. A–C, L–O. Scanning electron micrographs of ♂ genitalia. D–K. Scanning electron micrographs of ♀ genitalia. A–G. Plagiognathus chengshingi sp. nov. H–N. P. yomogi. O. P. amurensis. A, L. Genital segment (pygophore) with phallotheca and parameres, dorsal view. B−C, M−O. Vesica. D, H. Genital chamber, dorsal view. E−F, I−J. Posterior wall. G, K. Apex of ovipositor (gonapophysis I). Abbreviations: see Material and methods.

Fig. 7. Female genital chamber of Plagiognathus spp. in dorsal view. A. P. chengshingi sp. nov. B. P. marinoccidens sp. nov. C. P. yomogi. D. P. amurensis. Abbreviations: see Material and methods.