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New species of Hybristodryinus Engel (Hymenoptera, Dryinidae) from mid-Cretaceous amber of northern Myanmar, with notes on their possible hosts
expand article infoMassimo Olmi, Hua-Yan Chen§, Chungkun Shih|, Patrick Müller#, Leonardo Capradossi¤, Dong Ren|, Evgeny E. Perkovsky«», Adalgisa Guglielmino˄
‡ Tropical Entomology Research Center, Viterbo, Italy
§ Sun Yat-sen University, Guangzhou, China
| Capital Normal University, Beijing, China
¶ National Mu­seum of Natural History, Smithsonian Institution, Washington, DC, United States of America
# Unaffiliated, Südwestpfalz, Germany
¤ Unaffiliated, Tuscania, Italy
« National Academy of Sciences of Ukraine, Kiev, Ukraine
» Borissiak Paleontological Institute of the Russian Academy of Sciences, Moscow, Russia
˄ University of Tuscia, Viterbo, Italy
Open Access

Abstract

Two new species of Hybristodryinus Engel, 2005, are described from mid-Cretaceous amber of northern Myanmar: H. castaneus sp. nov. (based on one male) and H. zaifui sp. nov. (based on one female). Keys to the females and males of Hybristodryinus species are modified to include the two new taxa. A syninclusion, a nymph of Cixitettiginae (Perforissidae), present in the same amber piece containing H. zaifui, is studied. This syninclusion, together with the presence of Antennal Dorsal Organs (ADOs) in Hybristodryinus, suggests that Perforissidae are possible hosts of Hybristodryinus.

Keywords

Chrysidoidea, Cixitettiginae, host, keys, Perforissidae, taxonomy

Introduction

Dryinidae (Hymenoptera: Chrysidoidea) are parasitoids and often also predators of leafhoppers, planthoppers and treehoppers (Hemiptera, Auchenorrhyncha) (Guglielmino et al. 2013). They comprise 16 subfamilies, 50 genera and almost 1900 species worldwide (Olmi et al. 2020).

Mid-Cretaceous Kachin (Myanmar) amber (about 99 Ma) is the famous Burmese amber (Lin et al. 2019; Cao et al. 2020; Zhao et al. 2020), different from the recently discovered Campanian Tilin amber (Zheng et al. 2018) and Albian Hkamti amber (Xing and Qiu 2020). Dryinidae from Burmese amber are not common. Lists of the species known from this type of amber, reported by Perkovsky et al. (2019, 2020a) and Tribull et al. (2020), include the following subfamilies and genera: Anteoninae: Burmanteon Engel, 2003 (one species); Burmadryininae: Burmadryinus Olmi, Xu & Guglielmino, 2014 (one species); Dryininae: Dryinus Latreille, 1804 (13 species); Hybristodryinus Engel, 2005 (14 species); Pseudodryinus Olmi, 1991 (one species); Palaeoanteoninae: Palaeoanteon Olmi, 2000 (one species); Raptodryininae: Raptodryinus Olmi, Perkovsky, Martynova, Contarini, Bückle & Guglielmino, 2020 (one species).

The extinct genus Hybristodryinus is known only from Burmese amber (Perkovsky et al. 2019). With 14 described species, it is the most diverse genus of pincer wasps from that type of amber (Perkovsky et al. 2020a; Tribull et al. 2020).

In this study, we examined a small collection of dryinids from Burmese amber and recognized two additional new species, described below. In addition, we studied a syninclusion, represented by a nymph of a possible host of Hybristodryinus.

Material and methods

The descriptions follow the terminology used by Olmi et al. (2019) and Perkovsky et al. (2019). The measurements reported are relative, except for the body length (head to abdominal tip, without the antennae). In the descriptions, POL is the distance between the inner edges of the lateral ocelli; OL is the distance between the inner edges of a lateral ocellus and the median ocellus; OOL is the distance from the outer edge of a lateral ocellus to the compound eye.

The term “metapectal-propodeal complex” is here used in the sense of Kawada et al. (2015). It corresponds to the term “propodeum” sensu Olmi (1984).

In all monographs on Dryinidae (Olmi 1984; Xu et al. 2013; Olmi and Virla 2014; Olmi and Xu 2015; Olmi et al. 2019), different names of the cells and veins of the fore wing were used. They are here used in the sense of Azevedo et al. (2018), and Perkovsky et al. (2019). The correspondence between old and new names is the following (the first name is the old name): median cell = radial cell (R); submedian cell = first cubital cell (1Cu); marginal cell = second radial 1 cell (2R1); stigmal vein = second radial cross & radial sector (2r-rs&Rs); metacarp = poststigmal abscissa of radial 1 (PostabR1). In the text, cells and veins are named by their respective abbreviations, including costal cell (C).

The term “ADOs” (= Antennal Dorsal Organs) is here used in the sense of Riolo et al. (2016). It corresponds to the term “rhinaria” sensu Olmi (1984) and Xu et al. (2013). According to Riolo et al. (2016), ADOs are sensory structures that might mediate the antennal responses to vibratory stimuli. As far as we know, they are present only in the antennae of dryinid females attacking Fulgoromorpha (Olmi 1984). Antennae without ADOs are present mainly in species that are parasitoids of Cicadomorpha.

Because of the nature of the fossils and distortions sometimes caused by artifacts, the word “apparently” is used when describing characters for which there is slight uncertainty about the true condition or where a false impression is obtained at first sight.

The types of all fossil species of Hybristodryinus were examined. The type material of the new taxa studied in this paper is deposited in the collections of the Key Lab of Insect Evolution and Environmental Changes, the College of Life Sciences, Capital Normal University, Beijing, China (CNUB) and the Department of Agriculture and Forest Sciences (DAFNE), University of Tuscia, Viterbo, Italy (DAF).

Results

Generic placement

The new species described in this paper have been placed in the genus Hybristodryinus, because they fit the generic diagnosis reported below.

Hybristodryinus Engel, 2005

Hybristodryinus Engel 2005: 486. Type species: Hybristodryinus resinicolus Engel 2005, by monotypy and original designation.

Diagnosis of the genus

Female: Macropterous; occipital carina complete; mandible quadridentate, with teeth becoming regularly progressively larger from dorsal to ventral tooth; palpal formula 6/3; antenna without tufts of long hairs; antennal ADOs present; disc of metapectal-propodeal complex with posterior corners strongly projected posteriorly; fore wing with three cells enclosed by pigmented veins (C, R, 1Cu); chela with rudimentary claw; protarsomere 5 less than twice as broad as enlarged claw; enlarged claw shorter than protibia; tibial spurs 1/1/1 or 1/1/2. Male: Macropterous; antenna with scape much broader than pedicel; palpal formula 6/3; occipital carina complete; mandible with four irregular teeth; epicnemium visible, because lateral regions of prothorax not continuous with mesopleura; mesopleuron protruding laterally; fore wing with three cells enclosed by pigmented veins (C, R, 1Cu), 2r-rs&Rs vein and pterostigma; fore wing with PostabR1 slightly shorter than pterostigma; tibial spurs 1/1/2.

Hybristodryinus castaneus Olmi, Guglielmino & Chen, sp. nov.

Figure 1

Diagnosis

Male: macropterous, with antennomere 9 about six times as long as broad (Fig. 1E); face without long deep longitudinal furrow (Fig. 1D); posterior margin of vertex not deeply excavated medially (Fig. 1C); lateral ocelli not touching occipital carina; notauli complete, posteriorly separated (Fig. 1C).

Figure 1. 

Hybristodryinus castaneus sp. nov., male, holotype A habitus, dorsal view B habitus, ventral view C head and mesosoma, dorsal view D head and mesosoma, ventral view E antenna F fore wing.

Description

Male. Macropterous (Fig. 1A, B); length 1.4 mm. Completely dark brown. Antenna filiform, about as long as body, with setae very short. Scape about as broad as pedicel. Antennomeres in following proportions: 5:4:8:9:9:9:8:8:6:7. Antennomere 9 about six times as long as broad (Fig. 1E). Head with sculpture not visible; face without long deep median longitudinal furrow; mandible with teeth not visible; frontal line not visible; occipital carina complete, laterally not reaching eyes; ocellar ratio: POL:OL:OOL:OPL = 1:1:2:1; temple more than twice as long as OOL (5:2); greatest breadth of lateral ocellus as long as OOL; posterior margin of vertex not excavated medially (Fig. 1C); occiput deeply excavated. Palpal formula 6/3. Mesosoma much longer than head (30:10) and metasoma (30:20). Pronotum with lateral regions not protruding. Mesoscutum shiny, with sculpture not visible, slightly shorter than head (9:10), much longer than mesoscutellum (9:5). Notauli complete, posteriorly separated (Fig. 1C); minimum distance between notauli longer than OOL (3:2). Mesoscutellum shiny, with sculpture not visible. Metanotum and metapectal-propodeal complex not visible. Epicnemium not visible. Mesopleuron not visible. Fore wing hyaline, without dark transverse bands (Fig. 1F). Stigmal vein (2r-rs&Rs) with angle between proximal and distal parts, with distal part much longer than pterostigma (12:8). Second radial 1 cell (2R1) open. Pterostigma much longer than broad (9:2). Metacarpus (PostabR1) slightly shorter than pterostigma (7:9). Fore leg ratio: ? (coxa not visible, because it is hidden by an air bubble): 5 (trochanter): 16 (femur): 12 (tibia): 8 (protarsomere 1): 3 (protarsomere 2): 3 (protarsomere 3): 2 (protarsomere 4): 4 (protarsomere 5). Protrochanter more than four times as long as broad (5:1). Mid leg ratio: 7 (coxa): 4 (trochanter): 17 (femur): 15 (tibia): 9 (mesotarsomere 1): 3 (mesotarsomere 2): 2 (mesotarsomere 3): 1.5 (mesotarsomere 4): 3 (mesotarsomere 5). Mesotrochanter more than twice as long as broad (4:1.5). Hind leg ratio: 8 (coxa): 4 (trochanter): 17 (femur): 21 (tibia): 10 (metatarsomere 1): 4 (metatarsomere 2): 3 (metatarsomere 3): 2 (metatarsomere 4): 3 (metatarsomere 5). Tibial spurs 1/1/2.

Female. Unknown.

Material examined

Holotype: male (DAF3869), Myanmar: specimen in mid-Cretaceous Burmese amber (about 99 Ma). Obtained from a mine situated in Northern Myanmar, Kachin State, Tanai Township, Hukawng Valley, SW of Tanai City (DAF).

Etymology

The species is named castaneus (Latin adjective meaning “brown”) because of its dark brown colour.

Remarks

H. castaneus is similar to H. konbaung Perkovsky, Olmi, Müller & Martynova, 2019, known from Burmese amber, for the following characters: face without a long deep longitudinal furrow, lateral ocelli not touching the occipital carina, posterior margin of the vertex not excised medially, notauli complete and separated posteriorly. However, the antenna of H. castaneus is slenderer, with antennomere 9 about six times as long as broad (less slender in H. konbaung, with antennomere 9 about twice as long as broad). Perkovsky et al. (2019) indicate “pronotum with lateral regions protruding” among the characters of the generic diagnosis. However, this character is not visible in all known males (as in H. pyu Perkovsky, Olmi, Müller & Martynova, 2019) and it is not present in H. castaneus sp. nov. (see description above). Except this character, H. castaneus meets with all other generic diagnosis characters of Hybristodryinus. Therefore, we update the diagnosis of the genus by excluding this character.

Hybristodryinus zaifui Chen, Olmi & Perkovsky, sp. nov.

Figures 2, 3

Diagnosis

Female: macropterous, with disc of pronotum shaped as an isosceles triangle; notauli incomplete, reaching about 0.7 × length of mesoscutum (Fig. 2C).

Figure 2. 

A right, Hybristodryinus zaifui sp. nov., female, holotype, habitus, latero-dorsal view; left, nymph of Perforissidae (Perforissidae), ventral view B left, Hybristodryinus zaifui sp. nov., female, holotype, habitus, latero-ventral view; right, nymph of Cixitettiginae, habitus, dorsal view C, D Hybristodryinus zaifui sp. nov., female, holotype: C head and mesosoma, dorsal view D head and mesosoma, latero-ventral view E antenna, arrows indicate the ADOs in the antennomeres 6–10 (one ADO per antennomere, except two ADOs in antennomere 10) F wings, 1Cu = cubital 1 cell, 2r-rs&Rs = stigmal vein, C = costal cell, P = pterostigma, R = radial cell.

Description

Female. Macropterous (Fig. 2A, B); length 1.8 mm. Apparently completely brown-testaceous. Antenna clavate, apparently almost hairless; antennomeres in following proportions: 6:4:5:4:4:3.5:3.5:3:3:4; antenna about three times as long as head (37:12), reaching metapectal-propodeal disc. ADOs apparently present in antennomeres 6–10 (Fig. 2E). Flagellomeres longer than wide; antennomere 9 about three times as long as broad. Head excavated, apparently unsculptured; clypeus not visible; mandible not visible; face slightly concave; occipital carina complete (Fig. 2C); vertex without two longitudinal keels connecting lateral ocelli to occipital carina; occiput deeply excavated; eye normally bulging; ocellar ratio: POL:OL:OOL:OPL = 1:2:2:1; temple about twice as long as OOL (4:2); greatest breadth of lateral ocellus longer than POL (2:1); frontal line apparently complete; palpal formula probably 6/3 (labial palpus not distinct). Pronotum crossed by anterior deep transverse impression between anterior collar and disc; disc humped, apparently isosceles triangle shaped, not deeply medially longitudinally excavated; posterior collar absent; anterior surface of pronotum not sculptured by longitudinal striae; sculpture of disc not distinct; pronotum shorter than head (6:12); anterior collar of pronotum much shorter than disc (2:4); pronotal tubercle reaching tegula. Epicnemium not visible. Mesoscutum apparently unsculptured, longer than pronotum (10:6). Notauli incomplete, reaching about 0.7 × length of mesoscutum (Fig. 2C). Mesoscutellum apparently unsculptured, shorter than mesoscutum (4:10). Metanotum shorter than mesoscutellum (2:4), with sculpture indistinct. Metapectal-propodeal complex shorter than mesoscutum (5:10), with disc reticulate rugose, with areolae very broad, with posterior corners lamina shaped, strongly projected posteriorly (Fig. 2D); propodeal declivity not visible. Fore wing (Fig. 2F) apparenly hyaline, not darkened, with the usual venation of Dryininae; pterostigma much longer than broad (10:2); second radial cell (2R1) open; stigmal vein (2r-rs&Rs) regularly curved; fore wing with usual three basal cells (C, R, 1Cu) clearly enclosed by pigmented veins. Hind wing not visible. Fore leg ratio: 7 (coxa): 5 (trochanter): 15 (femur): 9 (tibia): ? (tarsus only partly visible); enlarged claw (Fig. 3A, B) slightly shorter than protarsomere 5; protrochanter very slender and long, with long and slender proximal stalk, broadened after half-way; protrochanter less than seven times as long as broad (5:1); protarsomere 3 produced into hook; rudimentary claw not visible; arolium not visible; enlarged claw apparently with one subapical tooth, with one row of lamellae (number of lamellae uncertain). Protarsomere 5 (Fig. 3B) with inner side not visible; lamellae of protarsomere 5 not visible. Mid leg ratio: 5 (coxa): 3 (trochanter): 13 (femur): 12 (tibia): 16 (tarsus). Mid trochanter short and broad. Hind leg ratio: 6 (coxa): 3 (trochanter): 18 (femur): 17 (tibia): 21 (tarsus). Metasomal petiole very short. Metasoma (excluding sting (Fig. 3C)) longer than mesosoma (39:27). Tibial spurs 1/1/2.

Figure 3. 

Hybristodryinus zaifui sp. nov., female, holotype A fore leg, 5t = protarsomere 5, Ec = enlarged claw B claw C sting.

Male. Unknown.

Material examined

Holotype: female (CNN-HYM-MA 2017087), Myanmar: specimen in mid-Cretaceous Burmese amber (about 99 Ma). Obtained from a mine situated in Northern Myanmar, Kachin State, Tanai Township, Hukawng Valley, SW of Tanai City (CNUB).

Etymology

The new species is named after the late Prof. Zaifu Xu (South China Agricultural University, Guangzhou, Guangdong, China), for his important contribution to the study of Chinese Dryinidae.

Remarks

For its isosceles triangle shaped pronotal disc, H. zaifui is similar to H. nalae Perkovsky, Olmi, Müller & Martynova, 2019, H. concavifrons Perkovsky, Olmi, Müller & Martynova, 2019, H. resinicolus Engel, 2005 and H. ligulatus Perkovsky, Olmi, Müller & Martynova, 2019. However, H. zaifui has incomplete notauli (Fig. 2C), reaching about 0.7 × length of mesoscutum, whereas in the other species the notauli are complete.

Partial keys to species of Hybristodryinus*

Females

1 Disc of pronotum isosceles triangle shaped (fig. 2A in Perkovsky et al. 2019) 2
Disc of pronotum with normal shape, not isosceles triangle shaped (fig. 8A in Perkovsky et al. 2019) 6
2 Notauli incomplete, reaching about 0.7 × length of mesoscutum (Fig. 2C) H. zaifui sp. nov.
Notauli complete, posteriorly separated (fig. 2A in Perkovsky et al. 2019) 3
3 Pronotum with disc deeply excavated longitudinally H. nalae Perkovsky, Olmi, Müller & Martynova
Pronotum with disc not deeply excavated longitudinally 4
4 Enlarged claw with two subapical teeth H. concavifrons Perkovsky, Olmi, Müller & Martynova
Enlarged claw without subapical teeth (fig. 7C in Perkovsky et al. 2019) 5
5 Enlarged claw with distal apex sharp H. resinicolus Engel
Enlarged claw with distal apex spoon-shaped (fig. 7C in Perkovsky et al. 2019) H. ligulatus Perkovsky, Olmi, Müller & Martynova

Males

2 Notauli incomplete, reaching about 0.5–0.9 × length of mesoscutum (fig. 5A in Perkovsky et al. 2019) 3
Notauli complete, posteriorly separated (fig. 10A in Perkovsky et al. 2019) 4
3 Notauli reaching about 0.5 × length of mesoscutum H. kayin Perkovsky, Olmi, Müller & Martynova
Notauli reaching about 0.9 × length of mesoscutum H. karen Perkovsky, Olmi, Müller & Martynova
4 Lateral ocelli touching occipital carina (fig. 10A in Perkovsky et al. 2019) H. pyu Perkovsky, Olmi, Müller & Martynova
Lateral ocelli not touching occipital carina 5
5 Antenna slenderer, with antennomere 9 about six times as long as broad (Fig. 1E) H. castaneus sp. nov.
Antenna less slender, with antennomere 9 about twice as long as broad H. konbaung Perkovsky, Olmi, Müller & Martynova

Discussion

Following the descriptions of the above two new taxa, the number of known Hybristodryinus species has increased from 14 to 16 (Perkovsky et al. 2019; Tribull et al. 2020; present paper), indicating that this extinct genus of Dryininae is the most diverse from Burmese amber, based on the known records. However, the main problem of this genus is the significant sexual dimorphism between the male and the female, so that it is impossible to associate the opposite sexes based on morphologic characters. This extreme sexual dimorphism is common to almost all pincer wasps (except the subfamily Aphelopinae, whose females are often similar to males, so that the association of the opposite sexes is less difficult). Males and females of extant species can be associated by rearing or DNA analysis, which apparently are not applicable to species in amber. Although males and females of this genus have been assigned to different new species, some of them are possibly the opposite sexes of one species. Therefore, currently there are two separate keys for Hybristodryinus species, one for females and one for males.

In the same subfamily Dryininae, Dryinus (13 species, see Martynova et al. 2020) is another relatively diverse genus in Burmese amber. However, Dryinus is an extant genus and has been reported not only from Burmese amber, but also from Priabonian Baltic, Scandinavian and Rovno amber (nine species, see Martynova et al. 2020; Perkovsky et al. 2020b), amber from upper Cenomanian Taimyr (Nizhnyaya Agapa River, Siberia, one species), Campanian Medicine Hat (Canada, one species) and Middle Miocene (Mexico, one species; Dominican Republic, nine species) (Martynova et al. 2020). In conclusion, there are 34 species of Dryinus reported from amber, much more than those of Hybristodryinus.

The hosts of Hybristodryinus are unknown, whereas the extant Dryinus are known to parasitize and prey on nymphs and adults of many Fulgoromorpha families: Acanaloniidae, Cixiidae, Dictyopharidae, Flatidae, Fulgoridae, Issidae, Lophopidae, Ricaniidae and Tropiduchidae (Olmi 1999; Guglielmino et al. 2013).

In Fig. 2A, B, H. zaifui is close to a nymph of unidentified Cixitettiginae (Hemiptera, Auchenorrhyncha, Perforissidae), a subfamily of extinct planthoppers known from Cretaceous amber (Barremian Lebanese, Barremian Jordanian, Albian Spanish, Cenomanian Burmese, Santonian Taimyr) and Aptian Bon Tsaagan Marl (Shcherbakov 2007; Petrulevicius et al. 2014; Rasnitsyn et al. 2016; Zhang et al. 2017; Perkovsky and Vasilenko 2019; Luo et al. 2020). Two genera and three species of the subfamily Cixitettiginae were described from Burmese amber (Luo et al. 2020); additional new taxa were reported, but not named (Shcherbakov 2007).

In Hybristodryinus, the antenna has the ADOs, which are sensorial structures present in dryinid females parasitizing Fulgoromorpha (Martynova et al. 2020). Perforissidae belong to Fulgoromorpha and therefore they could be hosts of Hybristodryinus. As mentioned previously, in mid-Cretaceous Burmese amber the most common dryinids were species of Dryinus and Hybristodryinus, both with antennal ADOs (Perkovsky et al. 2019; Martynova et al. 2020). Hybristodryinus is an extinct genus, whereas Dryinus is not extinct. The morphology of these two genera is similar (differences illustrated in Martynova et al. 2020 and Perkovsky et al. 2019) and cannot explain why one genus is extinct and the other is not. It could be hypothesized that Hybristodryinus is extinct as their hosts became extinct (Perkovsky et al. 2019). From this point of view, as Perforissidae are extinct planthoppers, they are perfect as one of the hosts of Hybristodryinus. Finding of perforissids with a thylacium of dryinids could strengthen the above hypothesis.

The above conclusion contrasts with the hypothesis proposed by Perkovsky et al. (2019) and Martynova et al. (2020), who asserted that Perforissidae are less likely hosts of Hybristodryinus, because they are well known from Baeomorpha realm (see Perkovsky and Vasilenko 2019 and references therein), where Hybristodryinus is unknown, and are scarce from Burmese amber. However, already two genera and three species of Cixitettiginae (Perforissidae), were described from Burmese amber (Luo et al. 2020), indicating that Perforissidae from Burmese amber were more diverse than expected.

Acknowledgments

The authors are grateful to Jacek Szwedo (Laboratory of Evolutionary Entomology, Department of Invertebrate Zoology and Parasitology, Faculty of Biology, University of Gdańsk, Poland) and Dmitry Shcherbakov (A. A. Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow, Russia) for the identification at family and subfamily levels of the nymph of Cixitettiginae (Perforissidae) photographed close to Hybristodryinus zaifui in Fig. 2A, B.

This research was carried out in the frame of the MIUR (Italian Ministry for Education, University and Research) initiative “Department of excellence” (Law 232/2016).

Dong Ren was supported by the National Natural Science Foundation of China (No. 31730087), Project of High-level Teachers in Beijing Municipal Universities (IDHT20180518), and Program for Changjiang Scholars and Innovative Research Team in University (IRT-17R75).

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1 Modified from Perkovsky et al. 2019.