On the horns of a dilemma: toward a better understanding of the Monacon species (Hymenoptera: Perilampidae) of Borneo Author Darling, D. Christopher Author Tatarnic, Nikolai J. text Journal of Natural History 2020 2020-09-23 54 9 723 734 journal article 9523 10.1080/00222933.2020.1776906 5635cce7-0195-420e-8d72-fe797c934aa6 1464-5262 4290496 Monacon gawai Darling ( Figures 1 (d), 2, 3, 4, SM1, SM2) Type locality Nanga Delok longhouse, Sri Aman Division , Sarawak ( 1° 13.998 ʹ N , 112° 01.252 ʹ E , 107 m ). Type material Holotype Female ( ROME176885 ), deposited at the Forest Research Centre, Sarawak Forestry Department, Kuching, ‘ MALAYSIA : Sarawak , Sri Aman Div. , Nanga Delok longhouse , 1° 13.998 ʹ N , 112° 01.252 ʹ E , 107 m , 1 June 2012 DC Darling ROM 2012103; Ex. 3-month cut log Baccaurea motleyana with Dinoplatypus pseudocupulatus (Schedl) ’, imaged ROM 24 November 2017 and 31 October 2019 . Thirty-five paratype females, 22 same data as Holotype: ROME179713 (BOLD COI sequence CDROM006-19, 411 bp); and 176834 , 179714–17973 and 13 labelled ‘ MALAYSIA : Sarawak , Sri Aman Div. , Nanga Talong longhouse , 1° 23.333 ʹ N , 111° 59.103 ʹ E , 246 m , 27 May 2018 DC Darling , N. Tatarnic ROM 2018526: Ex: durian log at mini-hydro dam, with ambrosia beetles ( Platypodinae )’: ROME179712 (BOLD COI sequence CDROM007-19, 431 bp) and ROME 179734 (BOLD COI sequence CDROM008-19, 430 bp), and ROM179735-17941 , 179752 , 179753 (X-Ray microtomography). Paratypes deposited at Forest Research Centre, Sarawak Forestry Department, Kuching, ROME , NHMUK , and USNM . Figure 2. Monacon gawai n.sp. (a) Lateral habitus. (b) Dorsal habitus. (c) Head, frontal. (d) Head, dorsal. (e) Head oblique. (f) Lateral pronotum and prepectus. (g) Scutellum, lateral view. (h) Metasoma and ovipositor, lateral view (Inset: apex of ovipositor, dorsal view). (a, b, f, g) Holotype, ROME176835. (c) Paratype, ROME179712. (d, e) Paratype, ROME139712. (h) Paratype, ROME179752. Additional Material Examined Malaysia ( 6 females ): Borneo , Sarawak sw. Gunung Buda , 64 km S. Limbang, 4°13 ʹ N 114° 56 ʹ E , 16–21.XI.1996 MT SL Heydon and S Fung ; Indonesia ( 5 females ): Sumatra , Aceh , Gunung Leuser Nat. Pk. , Ketambe Res. Sta.: 9–21 September 1989 . DC Darling , ROM 893089, 350 m , 3°41 ʹ N , 97°39 ʹ E . Malaise trap ( ROME176871 ); and 31 January 1990 . DC Darling. IIS 900003 ( ROME176864 ); Indonesia : Borneo , West Kalimantan , Gunung Palung Nat. Pk. , Cabang Panti Res. Sta. , 15 JUN-15 August 1991 . Darling , Ubaidillah , Sutrisno. IIS 910122, 100– 400 m , 1°15’S , 110°5 ʹ E , Malaise trap ( ROME176863 , 176872 , 176873 ) . Figure 3. Monacon species comparisons. (a ) M. modestum Bouček. Holotype and labels (Insets, Monacon gawai n.sp. Above, fore wing (Paratype ROME179712); Below, lateral mesosoma (Paratype ROME179735)). (b and c) Monacon gawai n.sp. , fore wing and venation. (b) Paratype female. (c) Female from Gunung Buda (Note: thickened band below marginal vein). Diagnostic description Females, slightly less than 3 mm in length. Black in colour, without iridescent reflections, except flagella, tegulae, trochanters, femora and tibiae brown, tibiae yellow. Wings hyaline, setose, type material without a thickened band below marginal vein ( Figures 3 (b), 4(b)). Monacon gawai is one of the very few species in southeast Asia with a completely demarcated clypeus ( Figure 3 (c)) – the lateral sutures are distinct and the epistomal sulcus is deep and crenulate. The flat clypeus has very low and setose tubercles ( sensu Bouček, 1980 ) near the lateral sutures and close to the anterior margin ( Figure 3 (c)). The clypeus, except for the tubercles, lacks setae and has very weak coriarious sculpture, in contrasts to the coarser sculpture on the rest of the face. The scrobal cavities are deep but restricted to the upper half of the face, convergent on the middle of the eye, with a distinct carina above ( Figure 3 (e)). The frontal horn is short in lateral view, less than one-half eye width, curved and triangular in lateral view ( Figure 3 (a)). The apex of the horn is rounded ( Figure 3 (b,d)). Monacon gawai is most similar to M. modestum Bouček , and will run to this species in the key provided by Bouček (1980) who also notes that M. modestum is “especially distinctive because of its simple horn and relatively flat and fairly shiny lower face with the tubercles clearly indicated but very low and placed nearer the eye margin that in other known species”. This statement now needs to be modified to include M. gawai . And based on the images of the holotype of M. modestum ( Figure 3 (a), B.M. Type 5.2700), the following characters differentiate M. gawai : slightly smaller is size, length 3 mm versus 3.5 mm and more gracile in lateral habitus, the mesosoma is lower in profile, with the mesoscutum and scutellum weakly curved (mesoscutum strongly convex and scutellum almost flat in M. modestum ) ( Figures 2 (a), 3(a) (inset), versus Figure 3 (a)). In addition, the fore wing is lighter in colour in M. gawai , not infuscate as in M. modestum ( Figures 2 (b), 3(a(inset),b,c) versus Figure 3 (a)). The only species of Monacon described from Sarawak is M. spinifrons (Cameron) . Based on key and description in Bouček (1980) , the drawing of the lateral view of the head ( Waterston 1922 , Fig. 17), and a specimen determined by Bouček, this species is regarded as distinct from both M. modestum and M. gawai . The horn of M. spinifrons is much broader at the base in lateral view, more triangular, and the clypeus is densely sculptured and setose. Etymology The specific epithet is a reference to Gawai Dayak, the annual harvest festival celebrated by the Dayaks of Borneo. The type material was collected in the vicinity of Iban longhouses, during or leading up to Gawai with the assistance of the Iban of Nanga Delok and Nanga Talong. Terima kasih amai amai! Distribution Monacon gawai is known only from Borneo. The type material is restricted to the specimens from the two longhouses in Sri Aman Division, Sarawak because COI sequences are only available from these two localities. These sequences, when aligned with ClustalW, had different bases at 4 of 411 sites, or a 99% similarity. COI sequences are not available for the specimens from Gunung Buda, Sarawak or Indonesia . In addition, these specimens have a thickened band below the marginal vein that is not found in any of the type specimens ( Figure 3 (c) cf. Figure 3 (b)). Otherwise, the specimens of M. gawai are morphologically very similar. Monacon modestum is not recorded from Borneo and is known from only three specimens, the holotype female (peninsular Malaysia ) ( Figure 3 ), and a female and male paratype from the Philippines ( Mindanao ). Host Association The holotype and 22 of the paratypes were collected in association with the ambrosia beetle Dinoplatypus pseudocupulatus (Schedl) (identification by Roger Beaver, Chiang Mai , Thailand ). High-resolution digital images of a male (ROME179937) and female (ROME179376) are archived in the ROM’s online collection. A COI sequence (BOLD CDROM009-19, 696 bp) was obtained for ROME179938 and there is 98.3% similarity to a specimen of this species from Lambir NP ( Sarawak ) (GenBank Acc. KR261319 ( Sarawak , Lambir NP)). The pinhole borers were associated with a fruit tree ( rambai: Baccaurea motleyana , Phyllanthaceae ), which was healthy but cut down 3 months before the collections were made. The paratypes from Nanga Talong were also associated with a fruit tree (durian, Durio species, Malvaceae ), which was recently cut down during the construction of a mini-hydro dam. Figure 4. Micro-CT images of Monacon gawai n.sp. (ROME179753) (a) Lateral view of body. (b) Cutaway view of head, showing inner structure of horn. (c) Cross-section of abdomen with eggs. For interactive pdf see supplementary data. Remarks Monacon gawai is most closely related to M. modestum . Currently, M. modestum is poorly characterised in terms of morphological variation, geographic distribution, host associations, and there are no genetic data available. Until there are more collections from Borneo and peninsular Malaysia in particular it will not be possible to evaluate the hypothesis that M. gawai i s a Borneo endemic. Should this species fall in synonymy, so be it, but the formal description of this species necessitates that this series of specimens, with paratypes distributed in numerous collections, and high-quality digital images and COI sequences archived at the ROM and BOLD, will have to be evaluated in future taxonomic studies of Southeast Asian Monacon . X-ray microtomography provided novel insights into the internal structure of Monacon ( Figure 4 and Supplemental Materials). The frontal horn is the most distinctive feature of all species of Monacon , and a horn on the supraclypeal area is unique to the genus and similarly developed in males and females. There has been little speculation on the function of the horn but Bouček (1980) suggested that the horn, the enlarged scrobal cavities and additional facial features “are apparently designed for the reception and protection of the antennae” and therefore associated with the emergence of adults from the galleries deep in the heartwood. It has been assumed that the horn was a cuticular process, but tomography reveals that there are tissues entering the horn and that these tissues also involve the inner surface of the clypeus ( Figure 4 (b), SM2). These could be glandular or sensory in function, which could suggest a role in host location. Females do not enter the galleries of the beetles but oviposit on the bark ( Figure 1 (d)) and the ovipositor is laterally compressed and has long setae toward the apex ( Figure 2 (h)Inset). The first-instar or planidial larvae enter the galleries and locate the host ( Darling and Roberts 1999 ). This is a risky strategy and may explain the large number of mature eggs in the abdomen of the female ( Figure 4 (c)). Also, striking was the size of the indirect flight muscles, in particular, the dorso-longitudinal muscles (SM Figure 4 (a)). A welldeveloped flight mechanism might be expected for a genus of parasitoids that attack hosts with patchy distributions in both time and space.