Neolygus Knight, 1917

Yasunaga, Tomohide, 2024, New species of the plant bug genus Neolygus Knight from Japan, Taiwan and Thailand (Hemiptera: Heteroptera: Miridae: Mirini), Zootaxa 5446 (4), pp. 451-487 : 452-453

Genus Neolygus Knight, 1917

Diagnosis: Neolygus is distinguished from other superficially similar genus groups (e.g. Anthophilolygus Yasunaga, Schwartz & Chérot, 2018 , Apolygus China, 1941, Miyamotolygus Yasunaga, Schwartz & Chérot , Prolygus Carvalho , Taylorilygus Leston, 1952 ) by the following combination of characters: body moderate in size (4–7 mm), oval to elongate oval; basic coloration mostly pale green (e.g. Figs. 1A–G, I, J , 3 ; some species with reddish or fuscous general coloration as in Fig. 1H ) but easily fading to pale brown in dry-preserved specimens ( Fig. 4A–C, GI ); dorsal surface shining, finely punctate, with uniformly distributed, pale, simple setae; vertex always with a continuous basal transverse carina ( Fig. 16B ); cuneus unicolorous and its apex not darkened; tibial spines pale brown or reddish brown, without dark spots at bases; parameres (cf. Figs. 6A–D, G–J , 7A–B, E , 10 , 12A–B, D ¬–E, 18E–F, 19G–H, 20K–N) with distinct sensory setae; left paramere L-shaped, with apical portion of sensory lobe more or less protuberant and hypophysis usually thickened apically; right paramere bird-head-shaped apically, with stout sensory lobe and developed, claw-like hypophysis; phallotheca expanded apically, usually with a small process (cf. Figs. 14A–G ); vesica principally with spiculum (SP), ventral sclerite (VS), median sclerite (MS) and basal sclerite (BS) (cf. Figs. 6E, K–L , 7C–D, F , 8C ¬–D, 9A–D, 11C, H, 12C, 14D); female genital chamber usually toughened with sclerites (SDS) (cf. Fig. 12F–G ), similar to those found in members of the genus Philostephanus Distant, 1904 or its allies ( Yasunaga & Schwartz 2007; Yasunaga 2016); sclerotized rings thick-rimmed, sometimes enlarged and contiguous to each other mesially (cf. Fig. 8G ); dorsal labiate plate usually with large dorsal sac (cf. Fig. 16K ) and strongly spinulate, posterior directed pair of sclerites on ventral surface (PPD) ( Fig. 12G ); posterior wall without dorsal structure; with widened lateral lobes, sometimes fused together or overlapped mesially (cf. Figs. 14B, E, H ); interramal lobes semi-circular (cf. Figs. 17B–C ) or squared (cf. Figs. 19K , 20D ); lateral lobes with uniformly distributed wide plate-like spinules (cf. Fig. 18K ); interramal lobes with predominately laterally distributed narrow sharply pointed spinules (cf. Figs. 14C, F, I ); interramal sclerite with faint median process ( Fig. 11K ).

Distribution. Holarctic and Oriental regions.

Discussion. In the Oriental Region and Asian warm temperate zones, genuine Neolygus members are not abundant, but a number of species belonging to Miyamotolygus , Prolygus or other genera instead of Neolygus predominate ( Yasunaga et al. 2018a). The species of other genera frequently have parameres of similar shape; however, each group is distinct in the pattern of vesical sclerites and female genitalic structures (cf. Yasunaga et al. 2018a). Neolygus species are considered cryophilic, and those inhabiting the Oriental Region are obviously restricted to cool highland zones generally grown with deciduous broadleaf vegetation (cf. Zheng et al. 2004; Yasunaga et al. 2012). Emergence of three Neolygus species known from the subtropical Ryukyus of southwestern Japan (the northernmost Oriental subtropics without highland area), N. kyushuensis (Yasunaga, 1991) ( Fig. 2A ), N. tokaraensis (Yasunaga 1991) ( Fig. 2A ) and N. yonanus n. sp. (see below description), is apparently limited to spring; these species diapause in the egg stage for more than 10 months.

The phylogenetic position of Neolygus within the tribe Mirini has yet to be clearly posited. It was regarded as a subgenus of Lygocoris Reuter, 1875 , but a plausible relationship between Neolygus and Lygocoris remains in doubt as homologous hypotheses for structures of the male and female genitalia are not yet realized ( Yasunaga 1991a, 2023; Yasunaga & Vinokurov 1999). The female genitalia of Neolygus species have been insufficiently employed for the classification. During the present examination, more than 20 Neolygus congeners were observed (e.g. Figs. 8E–H , 12F–G , 14E–F , 16J–O ). Several species have more or less asymmetrical genital chamber with partly sclerotized dorsal sac (e.g. Fig. 14F ) that is sometimes strongly protruded posteriorly and fused with anterior part of the posterior wall (e.g. Fig. 16K ). Similar structures are reported in the East Asian genus Philostephanus Distant, 1904 and its allies ( Yasunaga & Schwartz 2007; Yasunaga 2016), to which Neolygus may be related. Nonetheless, further critical analysis is required to document a significant portion of the Oriental Mirini and reliable elucidate their phylogenetic relationships.

Owning to lack of information on the female genitalia, it is currently difficult (or often impossible) to make exact identification of the Neolygus species by female specimens alone. As mentioned in my previous work (Yasunaga 2023), a large number of the described species are known only by the males, and numerous undetermined female specimens are remaining in public and personal collections. In addition, some species equally have uniformly pale green, immaculate body ( Figs. 3A–B , 4G–H ), whereas others have remarkable color variation ( Fig. 3C–F ). Reliable species identification is depend upon examination of the male genitalia for the time being, although the females of several congeners, with unique genitalic structures, can be correctly determined (e.g. Figs. 8G–H , 12F , 16M–O ). Continuing attempt to match up conspecific male and female is essential.

The majority of Neolygus species are univoltine and propagate on broadleaf shrubs or trees, particularly the flower buds or inflorescences (e.g., Yasunaga 2021; Noguchi et al. 2023). The eggs, oviposited into shoots, usually hibernate. Only a few species are known to inhabit conifers ( Kelton 1980; Yasunaga 2001). Several species are known as agricultural pests of economic importance injurious to fruit products or medicinal plants ( Knight 1927; Kelton 1982; Wheeler 2001; Yasunaga et al. 2018b; Yasunaga 2021). Miyazaki et al. (2019) observed that a female adult of Neolygus kyushuensis (Yasunaga) could survive for 32 days, reared with a synthetic diet composed of fermented milk beverage and dried larvae of chironomid midges (both commercially available). The methodology was also applied to rearing several 4th to 5th instar immature forms ( N. esakii and N. zhugei ), which successfully developed into the adult stage ( Noguchi et al. 2023; Yasunaga unpublished observation). These results imply that Neolygus members partially have zoophytophagous food habit.

Examination of pertinent Neolygus specimens revealed that N. tsugaruensis ( Yasunaga, 1992) [originally described as Lygocoris (Neolygus) tsugaruensis Yasunaga, 1992: 522 ] is a pale-colored variant of N. roseus (Yasunaga, 1991) ( Figs. 1H , 19L–O ). Accordingly, Neolygus tsugaruensis ( Yasunaga, 1992) syn. n. is herein proposed as a junior synonym of Neolygus roseus (Yasunaga, 1991) .

Figures

FIGURE 1. Habitus imagesof living individualsof Neolygus spp.A–B.N.autumnusn. sp.,male.C.N. honshuensis(Linnavuori). D. Same, female. E–G. N. chikanoshima n. sp., female. H. N. roseus (Yasunaga), female. I. N. fuscovultus n. sp., holotype female. J. N. chaiyaphum n. sp., holotype male.

FIGURE 2. Habitus images of living adults and final instar nymphs (C, F) of Neolygus spp. A–C. N. kyushuensis (Yasunaga). D–F. N. tiliicola (Kulik). G. N. tokaraensis (Yasunaga), female.

FIGURE 3. Habitus images of living individuals of Japanese Neolygus spp. A. N. flavoviridis (Yasunaga). C. N. hoberlandti (Kulik). C. N. lobatus (Linnavuori). D. Same, greenish variant lacking dark dorsal macula. E. N. pteleinus (Kerzhner). F. Same, pale variant lacking dark dorsal macula. G. N. nipponicus (Yasunaga), extremely darkened variant. H. Same, paler variant. I. N. esakii (Yasunaga). J. N. obesus (Yasunaga). K. N. juglandis (Kerzhner). L. N. similis (Yasunaga). M. N. longiusculus (Kulik) O. N. nemoralis (Kulik).

FIGURE 4. Ventral (E, F, H), lateral (C) and dorsal habitus images of Japanese Neolygus spp., dry-preserved specimens. A. N. autumnus n. sp., holotype male. B–C. Same, female. D–E. N. chikanoshima n. sp., male. F. holotype female. G–H. N. chichibumontis n. sp., holotype male. I. N. hasegawai n. sp., holotype male.

FIGURE 6. Male (A–E, G–L) and female (F, M) genitalia of Neolygus autumnus n. sp. (A−F) and N. honshuensis (Linnavuori) (G–M).A, C, G, I. Left paramere. B, D, H, J, Right paramere. E, K, L. Vesica. F, M. Female genital chamber. Scale bars 0.2 mm. Abbreviations – GP: secondary gonopore, MS: median sclerite, PH: phallotheca, SP: spiculum, VS: ventral sclerite.

FIGURE 7. Male genitalia of chichibumontis n. sp. (A−D) and N. nozakii Yasunaga (E–F). A. Apex of genital segment (pygophore) with parameres, dorsal view. B, E. Same, ventral view. C, F. Vesica, ventral view. D, Same, dorsal view (side of secondary gonopore opening). Scale bars 0.2 mm. Abbreviations – BS: basal sclerite, GP: secondary gonopore, MS: median sclerite, PH: phallotheca, SP: spiculum, VS: ventral sclerite.

FIGURE 8. Male (A–D) and female (E–H) genitalia of Neolygus hasegawai n. sp. (A−F) and N. flavoviridis (Yasunaga) (G–H). A. Apex of genital segment (pygophore) with parameres, dorsal view. B. Same, ventral view. C, F. Vesica, ventral view. D, Same, dorsal view (side of secondary gonopore opening). E, G. Female genital chamber. F, H. Posterior wall of bursae. Scale bars 0.2 mm.

FIGURE 10. Male genitalia of Neolygus yonanus n. sp. (A–D), N. chikanoshima n. sp. (E–F), N. kyushuensis (Yasunaga) (G–H) and N. tiliicola (Kulik) (I–J).A, C, H, I, Left paramere. B, D, G, J, Right paramere. E. Apex of genital segment (pygophore) with parameres, dorsal view. F. Same, ventral view. Scale bars 0.1 mm.

FIGURE 11. Male (A–C, F–H) and female (D–E, I–L) genitalia of Neolygus babai n. sp. (A–E), N. formosaroseus n. sp. (F–I) and N. fuscovultus n. sp. (J–L) A, F, Left paramere. B, G, Right paramere. C, H, Vesica. D, I, L, Female genital chamber. E, K, Posterior wall of bursae. J, Apex of ovipositor (gonapophysis I). Scale bars 0.2 mm.

FIGURE 12. Male (A–E) and female (F–G) genitalia of Neolygus rufifemoratus n. sp. (A–C), N.chaiyaphum n. sp. (D–E), N. zhugei (Yasunaga) (F) and N. nipponicus (Yasunaga) (G). A, E, Left paramere. B, D, Right paramere. C, Vesica. F, G, Female genital chamber (G: scanning electron micrograph). E, K, Posterior wall of bursae. J, Apex of ovipositor (gonapophysis I). Scale bars 0.1 mm. Abbreviations – GNP: gonapophysis, DLP: dorsal labiate plate, PPD: paired posterior plate extending from dorsal labiate plate, LOB, lateral oviduct, SED: seminal depository, SDS: sclerite on dorsal sac, SCR: sclerotized ring, SPG: spermathecal gland.

FIGURE 14. Scanning electron micrographs for Neolygus autumnus n. sp. (A−F) from Oita Pref. (A–C) and Kyoto Pref. (D–F), N. honshuensis (Linnavuori) (G−I) and N. chichibumontis n. sp., holotype male (J−O). A, D, G, O, Vesica. B, E, H, Posterior wall. C, F, I, Interramal lobe and lateral lobe of posterior wall. J, Head and pronotum, left lateral view. K, Metathoracic scent efferent system (left). L, Metatarsus. M, Pretarsal structure of metaleg. N, Apical pygophore (genital segment) with parameres, dorsal view. Abbreviations—BS: basal sclerite, GP: secondary gonopore, IRL: interramal lobe, IRS: interramal sclerite, LLB: lateral lobe, MS: median sclerite, PH: phallotheca, SP: spiculum, VS: ventral sclerite.

FIGURE 16. Scanning electronmicrographs forNeolygus hasegawai n.sp.(A−L), N.flavoviridis (Yasunaga)(M), N.hoberlandti (Kulik) (N) and N. makiharai (Yasunaga) (O). A, Anterior body, left lateral view. B, Head and pronotum. C, Thoracic pleura, left lateral view. D, Vestiture pattern of clavus and corium. E, Metatarsus. F, Pretarsal structure of metaleg. G, Apical pygophore (genital segment) with parameres, dorsal view. H, Vesica. I, Apex of vesical ventral sclerite. J, Genital chamber. K–O, Posterior wall.

FIGURE 17. Scanning electron micrographs for genitalia of Neolygus kyushuensis (Yasunaga) (A−C, G–I), N. tiliicola (Kulik) (D–F, J–L) and N. yonanus n. sp. (M–O). A, D, Genital chamber. B–C, E–F, Posterior wall [B, paratype from Okinawa Is.; C, from Nagasaki City; E, from Hamamasu, Hokkaido; F from North Korea]. G, J, Apical pygophore (genital segment) with parameres, dorsal view. M, Same, ventral view. H, K, N, Left paramere. I, L, O, Vesica.

FIGURE 18. Scanning electron micrographs for Neolygus babai n. sp. (A−K) and N. chaiyaphum n. sp., holotype male (L–O). A, Head and pronotum, frontal view. B, M, Thoracic pleura, left lateral view. C, N, Metatarsus. D, Pretarsal structure of metaleg. E, Left paramere. F, Right paramere. G–H, Vesica. I, Apex of ovipositor (gonapophysis I). J, Lateral and interramal lobes of posterior wall. K, Detail of lateral lobe. L, Head and anterior pronotum, left lateral view. O, Apex of pygophore (genital segment), left lateral view.

FIGURE 19. Scanning electron micrographs for Neolygus formosaroseus n. sp. (A−K) and N. roseus (Yasunaga) (L–O). A, Anterior body, left lateral view. B, L, Thoracic pleura, left lateral view. C, Metathoracic scent efferent system (left). D, M, Metatarsus. E, Pretarsal structure of metaleg. F, Apex of pygophore (genital segment), left lateral view. G, N, Left paramere. H, Right paramere. I, O, Vesica. J–K, Posterior wall.

FIGURE 20. Scanning electron micrographs for Neolygus fuscovultus n. sp., holotype female (A−F) and N. rufifemoratus n. sp., male (G–O). A, Head, frontal view. B, Pronotum, frontal view. C, Thoracic pleura, left lateral view. D–E, Posterior wall. F, Lateral lobe. G, Anterior body, left lateral view. H, Metathoracic scent efferent system (left). I, Metatarsus. J, Pretarsal structure of metaleg. K, Apex of pygophore (genital segment), left lateral view. L, Same, dorsal view. M, Left paramere. N, Right paramere. O, Vesica.