The silk-loving bug Embiophila sinica sp. nov. is described from Yunnan, southwestern China, representing the first record of the genus Embiophila (Heteroptera, Plokiophilidae) from Asia. The new species can be distinguished from its congeners by the different number of the spines on the fore – and mid-femora, and the numbers of the corial glands on the hemelytra. Photographs of the habitus and diagnostic characters, as well as living individuals in natural habitats, are provided. A key to Embiophila species is presented. The ecology of the new species and the distribution of Embiophila are briefly discussed.

Embiophilini, Embioptera, new species, Oriental Region, taxonomy

The Plokiophilidae comprises a small group of minute and distinctively behavioral bugs, with nine genera and 22 species known worldwide (Štys 1967; Henry 2020; Luo et al. 2021). Most of these bugs inhabit spider webs, while a minority of species have been observed living on the webs of embiopterans, one species is considered to be free living, and the living habits of the other species remain unknown (Štys and Baňař 2016; Schuh and Weirauch 2020; Luo et al. 2021).

The first species of Plokiophilidae, Arachnophila cubana China & Myers, 1929, was described as a member of the Microphysidae (China and Myers 1929). Due to the homonymy with Arachnophila Salvadori, 1874 (Salvadori 1874), China (1953) renamed Arachnophila China & Myers, 1929 as Plokiophila China, 1953, and described the second species, Embiophila myersi China, 1953, which inhabited the webs of the webspinners (the order Embioptera). This second species exhibits significant morphological differences from Plokiophila, which lead him to establish a new genus, Embiophila China, 1953, to accommodate it, while also elevating Plokiophilinae to the subfamilial rank within the Microphysidae. Carayon (1961) elevated Plokiophilinae as a distinct family and proposed the subfamilies Plokiophilinae and Embiophilinae. Carayon (1974) published the first monograph on Plokiophilidae, in which he described one new genus and seven new species, comprehensively elaborated on the morphology and habits of the family, and summarized previous knowledge. More species of the Plokiophilidae were discovered in the subsequent decades (Schuh and Štys 1991; Eberhard et al. 1993; Carpintero and Dellapé 2005; Schuh 2006; Popov 2008; Schuh et al. 2008). Schuh et al. (2015) downgraded the Embiophilinae to a tribe of the Plokiophilinae based on male and female genital structures, proposed a new subfamily, Heissophilinae, and a new tribe, Lipokophilini, and described two new genera and three new species. Subsequent new genera and new species of the Plokiophilidae were successively described since then (Štys and Baňař 2016; Luo et al. 2021), while the classification of the family has not been revised again.

The genus Embiophila is a unique group of the Plokiophilidae, whose species are generally living on the webs of embiopterans but also have been found to be free-living (Carayon 1974). China (1953) described Embiophila myersi based on specimens collected from Trinidad and Tobago and established Embiophila to accommodate this species. Carayon (1974) further divided Embiophila into the subgenera Acladina and Embiophila s. str. based on the venation of the hind wings, the length of the labial segments, and the morphology of the mid tibia, and described the second species of the genus, E. (A.) africana Carayon, 1974 from Congo. At the same time, he suggested that the genus Embiophila of the Old World might belong to the subgenus Acladina, while those of the New World belong to the subgenus Embiophila. The third species, E. (E.) maesi Carpintero & Dellapé, 2005, was discovered in Nicaragua (Carpintero and Dellapé 2005).

During the recent field investigations in Yunnan, southwestern China, we collected several specimens of a plokiophilid species on the webs of an unidentified embiopteran. Further examinations revealed that it represents a new species of Embiophila, and the description of the species constitutes the subject of this study. This new species represents the first record of Embiophila in China as well as Asia. The identification key to Embiophila species is updated, and the ecology of the new species and the distribution of the genus are briefly discussed.

Specimens examined in this study were deposited in the Entomological Museum of China Agricultural University, Beijing, China (CAU).

External and genital structures were examined using a Nikon SMZ745 stereoscopic microscope. Measurements (in mm) were taken using a Nikon SMZ18 with the Adobe Photoshop 2023. Male genitalia and female abdomen were macerated in 10% potassium hydroxide solution (KOH) at 60 °C for 3 h. Photographs were taken using a Canon EOS 7D Mark II camera, with the habitus pictures taken using the Nikon SMZ18, wings and female abdomen photographs taken using Olympus 4×/0.10, and photographs of the legs were taken with Olympus 10×/0.25, male genitalia photographs with Olympus 20×/0.40. Ecological photos were taken with a Nikon D5 camera with a Laowa 100 mm f/2.8 lens. Scanning electron micrographs were prepared using a Regulus 8100 Scanning Electron Microscope at State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China. Figure plates were prepared using Adobe Photoshop 2023. Distribution map was prepared using QGIS Desktop v. 3.34.11.

The classification system of Plokiophilidae follows Schuh et al. (2015). Morphological terminology mainly follows Carayon (1974) and Schuh et al. (2015). In terms of measurements, length of body is defined as the straight-line distance from the anterior tip of the head to the posterior end of the abdomen; maximum width of pronotum is defined as the distance between the two posterolateral angles of the pronotum; greatest length of pronotum is defined as the perpendicular distance from the anterior margin of the pronotum to the line connecting the two posterolateral angles.

Abbreviations used in the text and figures are as follows:

a acus;

ap articulatory apparatus;

cg corial gland;

Cgs corial glands;

Cu cubitus;

e egg;

lp left paramere;

M media;

R radius;

rp right paramere;

Sc subcostal;

sv secondary vein;

ts1 first segment of tarsus;

ts2 second segment of tarsus;

1An first anal vein.

In the seasonal rainforest in Pu’er, Yunnan, southwestern China, there are areas where tree leaves are relatively sparse, allowing sunlight to reach the moss and lichen-covered tree trunks. Embiopterans construct their nests there, with Embiophila sinica sp. nov. living on the web. Moss is not necessary, as we have also found traces of embiopterans and plokiophilid bugs on dry wood after logging. The number of adult bugs in each embiopteran web nest (approximately 1–7 adult embiopterans, and more than a dozen nymphs) is usually only 1–3, but nymphs can be quite high, reaching up to several dozen. The bugs exhibit strong locomotory capabilities, making them difficult to collect. When we strip away the webs for collecting, they quickly escape into the crevices of the trees. We collected some bugs from the field and fed them with mites (Acaridae) in the laboratory, and our observations once again confirmed the report by Carayon (1974) that the genus Embiophila feed on small arthropods within embiopteran webs. However, we did not observe them preying on embiopteran eggs, nymphs, and weak or dead adults, which still requires further observation. In the forest, with frequent rainfall, the webs of embiopterans provide safe and dry shelter for the web-lovers, while bugs help them clean various small arthropods, including mites, on the webs. Of course, these web-lovers can also survive independently of their hosts and can move freely on smooth surfaces without webs.

It is worth mentioning that from August 27 to September 12, 2024, we made two collections of Embiophila sinica sp. nov. at its type locality, collecting nine living female adults and numerous nymphs (at least 50), but no living male adults were found. The only male adult specimen was found to be dead on the web nest of embiopterans, and we speculated that it had been dead for a considerable amount of time. We believe that the males and females of the new species may exhibit significant differences in their emergence period and lifespan. Males in the same batch of nymphs are expected to emerge earlier than females, and they are likely to die shortly after mating, while females may survive for a longer period.

The known distribution of the four species of Embiophila is shown in Fig. 5. Embiophila myersi and E. maesi are distributed in Latin America, while E. africana is found in Africa. Embiophila sinica sp. nov. represents the first record of Embiophila in Asia. According to Carayon (1974), Embiophila was further subdivided into two subgenera, Acladina and Embiophila s. str., based on the venation of the hind wings, presence or absence of copulatory tubes in females, the relative lengths of the labial segments, and the morphology of the mid tibiae. The subgenus Embiophila contains the New World species, while the subgenus Acladina is restricted to the Old World. The subgenus Acladina is characterized by the following diagnostic traits: labial segment IV less than or equal to twice the length of segment III; mid-tibiae straight; hind wings lacking free distal branch of Cu; and presence of copulatory tubes in females. In our study, Embiophila sinica sp. nov., collected from China, aligns morphologically with the subgenus Acladina, thereby corroborating Carayon’s classification. Additionally, Carayon (1974) noted that at least one undescribed species of Acladina exists in Laos, which requires further investigation.

Embiophila sinica sp. nov. is the third species of Plokiophilidae discovered in China, following Plokiophiloides bannaensis Luo, Peng & Xie, 2021 and Heissophila macrotheleae Schuh, 2006 (Yin et al. 2023). Near the collection site of H. macrotheleae, P. bannaensis was also found, and this location is only 80 km away from the area where Embiophila sinica sp. nov. was discovered. Although Embiophila and even the Plokiophilidae currently exhibit extremely limited species diversity, the clustered distribution of E. sinica sp. nov. with two known relatives (H. macrotheleae and P. bannaensis) within a geographic range of less than 100 km suggests that the tropical and subtropical regions in southern China and the adjacent Indochina Peninsula, characterized by similar habitat conditions (e.g., high temperature and humidity, highly diversity of symbiotic species), may harbor Plokiophilidae species diversity beyond current recognition. This group may have a pan-tropical distribution, although confirming this hypothesis requires intensified sampling efforts. Nevertheless, their dispersal mechanisms and evolutionary history warrant further investigation.

We sincerely thank Weijia Wang (Beijing, China), Ruiyang Xian (Beijing, China), Anqiao Wu (Beijing, China) and Zehao Ma (Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, China) for their kind help during the field investigations.