Cycreon floricola borneanus, Arriaga-Varela, Emmanuel, Wong, Sin Yeng, Kirejtshuk, Alexander & Fikacek, Martin, 2018

Arriaga-Varela, Emmanuel, Wong, Sin Yeng, Kirejtshuk, Alexander & Fikacek, Martin, 2018, Review of the flower-inhabiting water scavenger beetle genus Cycreon (Coleoptera, Hydrophilidae), with descriptions of new species and comments on its biology, Deutsche Entomologische Zeitschrift 65 (1), pp. 99-115 : 107-111

Cycreon floricola borneanus ssp. n. Figs 1C, 3 E–H, 5 D–F, 6 A–B

Type locality.

Malaysia, Sabah, Tawau, Lahad Datu, Tawau Hills National Park, Kebun Botani, 305 m a.s.l., 4°23ʹ59.4ʺN 117°53ʹ17.2ʺE.

Type material.

Holotype (male: ZIN): "MALAYSIA: Sabah AR-2659 / Tawau, Lahad Datu, Tawau Hills / NP, Kebun Botani, 305m / 04°23ʹ 59.4N 117°53ʹ 17.2E / Schistamoglottis calyptrata group, / 8.vii.2016, Wong Sin Yeng, / P. C. Boyce & Zaiety binti Thomas". Paratypes: INDONESIA: Kalimantan Barat: Bengkayang Pajintan, Ayer Terjun Sibohe, 80 m, 0°51 ’55.8” N 109°2 ’25.1” E, flowering Schismatoglottis modesta , 2.ix.2017, Wong & Boyce lgt. (AR-2812) (39: NMPC, ZIN). Kalimantan Selantan: ʻS.O. Borneo / Grabowsky S. V.ʼ (1: ZMNH); Kendangan, 15.5.1882, Grabowsky S. V. [ca.: S 2.592552°, E 115.028244°] (5: ZMNH). MALAYSIA: Sabah: Tawau, Lahad Datu, Tawau Hills NP, HQ Area, 304 m, 4°23 ʹ51.2” N 117°53 ʹ25.1” E, flowering Alocasia longiloba complex, 6.vii.2016, Wong Sin Yeng & P.C.Boyce lgt. (AL-315) (1: ZIN); [same locality] flowering Schismatoglottis calyptrata complex, 7.vii.2016, Wong Sin Yeng & P.C.Boyce lgt. (AR-2641) (101: ZIN, NMPC, IBTP, KMNH, NHMW); Tawau, Lahad Datu, Tawau Hills NP, Air Terjun Bukit Gelas, 315 m, 4°24 ʹ48.4” N 117°53 ʹ29.3” E, flowering Gamogyne loi , 6.vii.2016, Wong Sin Yeng & P.C.Boyce lgt. (AR-2638) (12: ZIN, NMPC); Tawau, Lahad Datu, Tawau Hills NP, Trail to Bukit Gelas, 319 m, 4°24 ʹ37.0” N 117°53 ʹ38.8” E, flowering Homalomena hanneae complex, 6.vii.2016, Wong Sin Yeng & P.C.Boyce lgt. (AR-2636) (18: ZIN, NMPC); [same locality] flowering Schismatoglottis calyptrata complex, 7.vii.2016, Wong Sin Yeng & P.C.Boyce lgt. (AR-2652) (36: ZIN, NMPC); Tawau, Lahad Datu, Tawau Hills NP, Kebun Botani, 305 m, 04°23ʹ59.4ʺN 117°53ʹ17.2ʺE, flowering Schismatoglottis calyptrata complex, 8.vii.2016, Wong Sin Yeng, P.C.Boyce & Zaiety binti Thomas lgt. (AR-2659) (116: ZIN, NMPC, IBTP, KMNH, NHMW, BMNH); Kg. Moyog, Jln. Tambunan, Penampang, 12.xii.2009, H. Takizawa lgt [ca. N 5.888455°, E 116.235335°] (11: EIHE, KMNH, NMPC, IBTP); [same locality and collector] 30.x.2008 (7: EIHE, KMNH); [same locality and collector,] 13.ix.2008 (7: EIHE, KMNH, IBTP); Poring park, Ranau, 19-20.ix.2008, H. Takizawa lgt [ca. N 6.047067°, E 116.703231°] (7: EIHE, KMNH, IBTP); [same locality and collector] 25-26.ix.2008 (5: EIHE, KMNH. IBTP); [same locality and collector] 8-9.i.2010 (7: EIHE, KMNH, IBTP); [same locality and collector] 11.xii.2008 (3: EIHE, KMNH); [same locality and collector] 27.v.2010 (1: EIHE); [same locality and collector] 25.ii.2009 (2: KMNH); [same locality and collector] 10.vii.2008 (1: EIHE); [same locality and collector] 12.iii.2009 (1: KMNH); [same locality and collector] 29.viii.2013 (1: KMNH); [same locality and collector] 12.iii.2009 (1: KMNH); [same locality and collector] 4-5.iv.2008 (3: KMNH, IBTP); [same locality and collector] 7.x.2012 (2: KMNH); Kg. Kiapad, Inanam, Kota Kinabalu, 7.ix.2008, H. Takizawa lgt [ca. N 5.988388°, E 116,190333°] (16: KMNH, EIHE, IBTP, NMPC); [same locality and collector] 2.i.2010 (3: KMNH, EIHE); [same locality and collector] 10.xi.2012 (16: KMNH, EIHE, IBTP, NMPC); [same locality and collector] 6.xii.2008 (18: KMNH, EIHE, IBTP, NMPC); [same locality and collector] 6.iv.2013 (7: KMNH, EIHE, IBTP); [same locality and collector] 5.vii.2008 (22: KMNH, EIHE, IBTP, NMPC); [same locality and collector] 4.x.2008 (3: KMNH); [same locality and collector] 7.xi.2009 (1: KMNH); Ulu Senagang subts., Keningau, 31.i.-2.ii.2011, H. Takizawa lgt. [ca. N 5.362946°, E 116.028679°] (14: KMNH, EIHE, IBTP); [same locality and collector] 24-26.vii.2010 (2: KMNH); Kinabalu PHQ, Ranau, 17-19.iii.2008, H. Takizawa lgt. [ca. N 6.021639°, E 116.542751°] (1: EIHE); Kinabalu Park, HQ, Ranau, 5.iii.2010, H. Takizawa lgt. [ca. N 6.021639°, E 116.542751°] (3: EIHE, KMNH); [same locality and collector] 14.iii.2012 (1: KMNH); [same locality and collector] 8.vii.2010 (2: KMNH); [same locality and collector] 23-25.iii.2010 (1: EIHE); [same locality and collector] 27-28.v.2008 (2: KMNH); [same locality and collector] 13-14.v.2010 (1: EIHE); [same locality and collector] 23-25.viii.2008 (2: KMNH); [same locality and collector] 23-25.vii.2008 (1: KMNH); [same locality and collector] 1.ii.2010 (1: KMNH); [same locality and collector] 23-24.ix.2008 (1: KMNH); [same locality and collector] 17-19.x.2008 (1: KMNH); Muaya waterfall, Sipitang, 6-9.iii.2009, H. Takizawa lgt. [ca. N 4.903889°, E 115.760278°] (8: EIHE, KMNH, IBTP); Mahua waterfall, Crocker R. P., Tambunan, 26.vii.2011, H. Takizawa lgt [ca. N 5.797627°, E 116.408377°] (1: NMPC); Gn. Bombalai, Tawau Hills park, Tawau, 17.vi.2010, H. Takizawa lgt [ca. N 4.386858°, E 117.879748°] (4: EIHE, KMNH); Pk. Bundu Tuhan Kundasang, Ranau, 6.iii.2010, H. Takizawa lgt. [ca. N 5.996602°, E 116.528987°] (1: NMPC); Mesilau headgate, Kundasang, Ranau, 25.ii.2009, H. Takizawa lgt. [ca. N 6.044605°, E 116.596306°] (1: KMNH); Malangan, Kg. Tikolod, Tambunan, 12-14.iii.2010, H. Takizawa lgt. [ca. N 5.626763°, E 116.286933°] (1: EIHE); Pantai Barat, Kota Kinabalu, Inanam, Kionsom, Kionsom Waterfall, 230 m, 05 57 24.0N 116 12 25.3E, flowering Schismatoglottis corneri , 18.iv.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4683) (7: ZIN, NMPC). Sarawak: Serian, Pichin, between Sugun Karang and Tahang Sipukam, Sungai Kakas, 48 m, 1°06ʹ09.7ʺN 110°28ʹ11.8ʺE, flowering Schismatoglottis bulbifera , 28.vi.2014, Ooi Im Hin & Jeland ak Kisai lgt. (AR-4832) (1: ZIN); Kuching, Padawan, Puncak Borneo, Jungle Trail, 890 m, 1°07ʹ33.5ʺN 110°12ʹ57.4ʺE, flowering Ooia glans , 15.ix.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-93) (92: ZIN, NMPC, IBTP, KMNH, NHMW); Kuching, Padawan, Puncak Borneo, Sungai Semangas, 472 m, 1°08ʹ26.6ʺN 110°13ʹ36.1ʺE, flowering Ooia glans , 16.ix.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4979) (29: ZIN, NMPC, KMNH); Kuching, Matang, Kubah N.P., Sungai Bungen, 230 m, 1°36ʹ30.9ʺN 110°11ʹ35.0ʺE, flowering Ooia glans , 28.vii.2007, P.C.Boyce, Wong Sin Yeng & S.Maclean lgt. (AR-2118) (27: ZIN, NMPC, IBTP); [same locality] flowering Schismatoglottis mayoana , 28.vii.2007, Wong & Maclean lgt. (AR-2122) (1: ZIN); Kuching, Matang, Kubah N.P., Waterfall Trail, 190 m, 1°35ʹ40.2ʺN 110°10ʹ45.9ʺE, flowering Ooia glans , 28.vii.2007, P.C.Boyce, Wong Sin Yeng & S.Maclean lgt. (AR-2117) (10: ZIN, NMPC); Sri Aman, Lubok Antu, Sungai Engkari, Nanga Segerak, Sungai Serjanggut, 332 m, 1°24ʹ46.5ʺN 112°00ʹ18.5ʺE, flowering Ooia sp., 17.iii.2015, Wong Sin Yeng, P.C. Boyce & Bada ak Chendai lgt. (AR-5169) (11: ZIN, NMPC); Sri Aman, Lubok Antu, Engkilili, Tempat Rekreasi Sungai Raya, Sungai Raya, 13 m, 1°06ʹ49.2ʺN 111°30ʹ56.8ʺE, flowering Schismatoglottis calyptrata complex, 9.xii.2005, P.C.Boyce, Jeland ak Kisai, Jipom ak Tisai & Mael ak Late lgt. (AR-1632) (38: ZIN, NMPC, IBTP, KMNH); Sri Aman, Lubok Antu, Sungai Sepipit, 108 m, 1°11ʹ54.9ʺN 111°57ʹ29.4ʺE, flowering Schismatoglottis petradoxa , 27.vii.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4894) (1: ZIN); Kuching, Siburan, Kampung, Giam, Sugun Jawan, 70 m, 1°19ʹ20.7ʺN 110°16ʹ21.4ʺE, flowering Schismatoglottis giamensis , 20.vi.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2549) (56: ZIN, NMPC, IBTP, KMNH); Kuching, Siburan, Kampung Sikog, Air Terjun Baan Gong, 70 m, 1°20ʹ16.1ʺN 110°20ʹ09.6ʺE, flowering Schismatoglottis baangongensis , 26.vii.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2588) (63: ZIN, NMPC, IBTP, KMNH); Miri, Marudi, Long Lama, Mulu N.P., Trail to Deer Cave, 60 m, 4°02ʹ23.8ʺN 114°48ʹ54.6ʺE, flowering Phymatarum borneense , 5.viii.2006, P.C.Boyce, Wong Sin Yeng, Jeland ak Kisai & Mael ak Litis lgt. (AR-1931) (23: ZIN, NMPC); Miri, Marudi, Long Lama, Mulu N.P., Trail to Deer Cave, 60 m, 4°02ʹ02.0ʺN 114°49ʹ00.0ʺE, flowering Schismatoglottis muluensis , 6.viii.2006, P.C.Boyce, Wong Sin Yeng, Jeland ak Kisai & Mael ak Litis lgt. (AR-1941) (110: ZIN, NMPC, IBTP, KMNH, NHMW); Kuching, Siburan, Kampung Giam, Air Terjun Giam, 37 m, 01°19 ’11.2” N 110°16 ’11.4” E, flowering Homalomena giamensis , 07.ii.2016, P.C.Boyce, Jeland ak Kisai & Wong Sin Yen lgt. (AR-1691) (13: ZIN, NMPC); Kampung, Sungai Temaga, trail to Gunung Pueh, 82 m, 01°46 ’58.6” N 109°43 ’06.6” E, flowering Schismatoglottis , 23.iii.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4651) (1: ZIN); Kuching, Siburan, Air Terjun Baan Gong, 70 m, 01°20ʹ16.1ʺN 110°20ʹ09.6ʺE, flowering Homalomena borneensis , 26.vii.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2575) (11: ZIN, NMPC); Kuching, Siburan, Sugun Jawan, 50 m, 01°19 ’16.1” N 110°16 ’16.7” E, flowering Homalomena gastrofructa , 09.vi.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2559) (5: ZIN, NMPC); Miri, Niah N.P., Beside road margin, outside of the main entrance, 13 m, 03°49.598'N 113°45.683'E / 03°49.577'N 113°45.710'E, flowering Schismatoglottis , 30.iii.2014, Hoe Yin Chen lgt. (AR-4665) (2: ZIN); Kuching, Sematan, Sungai Temaga, trail to Gunung Pueh, 82 m, 01°46 ’58.6” N 109°43 ’06.6” E, flowering Homalomena caput-gorgonis , 23.iii.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4659) (2: ZIN); Kuching, Kampung Sebat Dayak, Air Terjun Sebat, 70 m, 01°48 ’05.6” N 109°43 ’09.6” E, flowering Piptospatha elongata , 21.iii.2014, Wong Sin Yeng & P.C.Boyce lgt. (AR-4367) (1: ZIN); Betong, Roban, Sebankoi, Taman Rekreasi Sebankoi, 154 m, 01°57ʹ27.4ʺN 111°26ʹ04.6ʺE, flowering Homalomena ibanorum , 05.xii.2005, P.C.Boyce, Jeland ak Kisai, Jepom ak Tisai, Mael ak Late & Wong Sin Yeng lgt. (AR-1538) (7: ZIN, NMPC); Kuching, Matang, Maha Mariamman Temple, trail to Indian Temple, 350 m, 01°35 ’25.7” N 110°13 ’12.8” E, flowering Homalomena matangae , 04.iii.2014, P.C.Boyce & Jeland ak Kisai lgt. (AR-230) (7: ZIN, NMPC); Kuching, Bau, Krokong, Gua Peri-peri, 30 m, 01°22 ’51.9” N 110°07 ’09.3” E, flowering Schismatoglottis , 09.v.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2445) (2: ZIN); Kuching, Bau, Gua Angin, 45 m, 01°24 ’54.8” N 110°08 ’08.2” E, flowering Schismatoglottis , 21.vi.2005, P.C.Boyce & Jeland ak Kisai lgt. (AR-1240) (8: ZIN, NMPC); Roban, Sebankoi, Taman Rekreasi Sebankoi, Site 1, 154 m, 01°57 ’27.4” N 111°26 ’04.6” E, flowering Schismatoglottis sarikeense , 07.ii.2010, Low Shook Ling lgt. (AR-3001) (4: ZIN); Kuching, Siburan, Kampung Sikog, Air Tejun Baan Gong, 70 m, 01°20ʹ16.1ʺN 110°20ʹ09.6ʺE, flowering Homalomena baangongensis , 26.vi.2009, P.C.Boyce & Wong Sin Yeng lgt. (AR-2574) (44: ZIN, NMPC, IBTP, KMNH); Kuching, Matang, Kubah N.P. Sungai Bungen, 230 m, 01°36ʹ30.9ʺN 110°11ʹ35.0ʺE, flowering Ooia glans , Ooi Im Hin lgt. (AR-2339) (2: ZIN); Kuching, Bau, Gua Angin, 45 m, 01°24 ’54.8” N 110°08 ’08.2” E, flowering Schismatoglottis , 21.vi.2005, P.C.Boyce & Jeland ak Kisai lgt. (AR-1240) (24: ZIN, NMPC). Miri, Miri, Marudi Long Lama, Mulu National Park, DC limestone, before Kenyalang trail junction, 65 m, 4°02 ’29.4” N 114°48 ’44.3” E, flowering Schismatoglottis muluensis , 25.xii.2017, SY Wang team lgt. (SK01) (38: NMPC); [same locality] DC limestone, before 2nd shelter, flowering Schismatoglottis colocasioideae , 27.xii.2017 (SK03) (11: NMPC); [same locality and host plant] 30.xii.2017 (SK07) (11: NMPC); [same locality] DC limestone, before Kenyalang trail junction, flowering Schismatoglottis muluensis , 1.i.2018 (SK10) (11: NMPC); [same locality] DC limestone, near Deer water cave, flowering Schismatoglottis muluensis , 1.i.2018 (SK11) (33: NMPC, IBTP); [same locality] DC limestone, canopy trail, flowering Schismatoglottis colocasioideae , 7.i.2018 (SK12) (13: NMPC); [same locality] BT right, flowering Schismatoglottis serratodentata , 8.i.2018 (SK13) (2: NMPC); [same locality and host plant] 23.i.2018 (SK17) (1: NMPC); [same locality] DC limestone, near Deer water cave, flowering Schismatoglottis pellucida , 30.i.2018 (SK18) (3: NMPC); [same locality] flowering Schismatoglottis multinervia , 31.i.2018 (SK19) (4: NMPC); [same locality and host plant] 3.ii.2018 (SK21) (3: NMPC); Kapit, Taman Rekreasi Sebabai, 84 m, 1°56 ’37.5” N 112°54 ’24.8” E, flowering Ooia havilandii , 22.ix.2017, Wong & Boyce lgt. (AR-3635) (23: NMPC, ZIN): Sarikei Bayong, Ulu Sarikei, Lubok Lemba, Rymah Nyuka, 55 m, 1°53 ’41.3” N 111°30 ’11.5” E, flowering Ooia secta , 3.vi.2017, Wong & Boyce lgt. (AR-2756) (1: NMPC); Kuching Lundu, Gunung Gading NP, waterfall 1, 200 m, 1°41 ’28.3” N 109°50 ’43.6” E, flowering Homalomena , 27.v.2017, Wong & Boyce lgt. (AR-2757) (3: NMPC); Sarikei Bayong, Ulu Sarikei, Lubok Lemba, Rymah Nyuka, 55 m, 1°53 ’41.3” N 111°30 ’11.5” E, flowering Schismatoglottis erumpens complex, 3.vi.2017, Wong & Boyce lgt. (AR-2753) (4: NMPC).

Diagnosis.

This species is very similar to Cycreon floricola floricola with which it shares most external characters and genital morphology. Cycreon floricola borneanus ssp. n. can be distinguished from C. floricola floricola by the shape of the pronotal punctation consisting only or largely of complete ring-like punctures. The dorsal coloration of C. floricola borneanus sp. n. is usually more uniform, with elytral colouration not much darker than pronotal one.

Description.

Measurements. 2.2-3.4 mm long (length of holotype: 2.9 mm), 1.8 –1.9× as long as wide, widest at basal fifth of elytra; weakly convex, 3.1 –3.3× as long as high (height of holotype: 2.8 mm). Colouration. Pale brown with weakly darker elytra (Fig. 1C).

Pronotum 2.2 × wider than long; 1.5 × wider at base than between anterior angles, 1.6 × wider than head including eyes. Punctation dense and shallow, consisting of complete ring-like impressions with one small setiferous puncture on posterior margin (Figs 4E, 5F), punctation of approximately same in size and density all over pronotum.

Elytra widest at anterior fifth, 1.1 –1.2× as long as wide, 2.9 –3.0× as long as pronotum, 1.1 × as wide as pronotum. Punctation on intervals composed of semicircular impressions with one setiferous puncture on posterior margin (Fig. 4F).

Variation.

In most specimens examined from Borneo, the pronotal punctation consists exclusively of completely ring-like punctures. However, in few localities on the north-western coast of Borneo the punctation of 5-20% of specimens shows a mixture of complete and incomplete rings. In the absence of genetic data, we are unable to analyze this variation in detail, and hence temporarily treat even these specimens as C. floricola borneanus .

Etymology.

The name of this species is derived from Borneo, the historical name of island where all the known specimens of this subspecies were collected.

Distribution.

The species seems to be widespread in Borneo, it is recorded from Indonesia: Kalimantan Barat and Kalimantan Selantan and Malaysia: Sabah, Sarawak (Fig. 7)

Biology.

This subspecies has been collected in inflorescences of a number of plant species belonging to the Araceae family. It was collected in high numbers in flowers of the genus Schismatoglottis : S. calyptrata , S. colocasioideae , S. erumpens complex, S. giamensis (Fig. 6G), S. mayoana , S. modesta , S. muluensis , S. multinervia , S. pellucida , S. petradoxa and S. serratodentata. It has been also collected in numbers close to one hundred specimens in an inflorescence of Ooia glans (Figs 6 H–I) and O. havilandii. Other known records of host plants include Alocasia longiloba complex (Fig. 6F), Gamogyne loi , several species of Homalomena (this paper) Phymatarum borneense and Schottarum sarikeense (Fig. 6 A–B) ( Low et al. 2016). According to H. Takizawa (pers. comm. 2017), C. borneanus can be found in aggregations in a wide range of aroid inflorescences from lowlands to montane areas (ca. between 100-1500 m a.s.l), mainly in flowers on small open places like trail sides in or near well-preserved primary or secondary forests, or along small streams.

Biology of Cycreon

All specimens of both subspecies of C. floricola have been collected in inflorescences of various Araceae genera, often in high numbers, indicating their tight association with this microhabitat. The fact that there were only two specimens of the genus known up to now likely correspond with the biology of Cycreon beetles, since no study of flower-inhabiting beetles associated with Araceae in the Malaysian Peninsula and Sunda islands was performed previously.

Low et al. (2016) studied the biology of insects associated with inflorescences of Araceae in Borneo and demonstrated that Cycreon floricola borneanus specimens are only present in the upper part of the inflorescences of Phymatarum borneense and Schottarum sarikeense , never in the pistillate zone (= bottom), and that they are not attracted by the smell of the inflorescences, unlike the co-occurring Chaloenus beetles ( Chrysomelidae ) and Colocasiomyia flies ( Drosophilidae ). Observations of few specimens covered by pollen grains were reported, but only Colocasiomia flies were considered as pollinators. Subsequent investigations of the pollination biology of the Schismatoglottis calyptrata complex ( Hoe et al. 2018) revealed that Cycreon floricola borneanus visited all the investigated species except Schismatoglottis calyptrata and S. laxipistillata , but their abundance differed based on host plant species: they were very abundant in S. giamensis , S. caesia and S. muluensis , but present in single or few specimens only in S. pseudoniahensis , S. pantiensis , S. adducta , and S. roh . Cycreon beetles were observed to feed on the exudations from the interpistillar staminodes, mated on the pistillate zone and remained inside the lower spathe chamber. They were also revealed as the most effective pollen carriers, carrying 6-15 times more pollen than Colocasiomyia flies and hence considered as secondary pollinators ( Colocasiomyia flies were 4-6 times more abundant and are hence considered as main pollinators). No hydrophilid larvae were found in the inflorescences, indicating that they may live in different microhabitat.

Mouthparts of Cycreon (Fig. 1 F–K) are unusual when compared to other members of the tribe Megasternini examined so far, differing from them in three aspects: (1) structure of the mandible with two large teeth on the apex (Fig. 1 F–G), (2) excision of the clypeus (varying from weak to very deep, depending of the species; Fig. 5), and (3) shape of the mentum, with deep anterior excision (Figs 1J, 2B, 5). The mandibles of other Megasternini examined so far bear simple apex (e.g., Fikáček 2010, Arriaga-Varela et al. 2018), while those of Cycreon have the apex deeply bifid and with two large teeth. When the mandible is examined in mesal view (Fig. 1H), both apical teeth are situated on sides of straight edge, and they become strongly abraded in some specimens (Fig. 1G). This may indicate that mandibular apex is used for processing of some hard/solid material, possibly for scraping organic material from internal parts of the aracean inflorescences, in agreement with the above observations by Hoe et al. (2018). The inspection of the gut contents of Cycreon floricola borneanus (Fig. 6 C–E) revealed that the midgut contains two components, both stained by safranine dye: (1) pollen grains of the respective plant species and (2) the heterogeneous organic matter which cannot be further identified; it does not seem to be just remains of crushed pollen grains, as no partially crushed pollen grains or remains of their exine were found (safranine stains various organic compounds including cellulose, lignine, glucosamines and cell nuclei, and does not allow detailed identification of this component - it may represent organic detritus scraped by the beetles from interior of the inflorescence). The presence of this unspecified organic matter in the intestines indicates that Cycreon beetles are not specialized pollen feeders, but the presence of pollen grains in the midgut content confirms that pollen is part of the diet and may be possibly digested. When compared to specialized pollen-feeding New Zealand genus Rygmodus ( Hydrophilidae : Cyclominae ) analyzed by Minoshima et al. (2018), important differences in mandible morphology can be found, confirming that Cycreon is not specialized pollen feeder: (1) mandibular apex is simple and spoon-like in Rygmodus , whereas strongly bifid in Cycreon , (2) mola is simply tuberculate in Rygmodus (a supposed adaptation to disrupt the pollen exina by grinding), but bears poriferous lamellae in Cycreon and all other hydrophilids examined. Unlike in Cycreon , the midgut of Rygmodus contains nearly exclusively pollen grains, with very little fine organic matter (see Minoshima et al. 2018: fig 4).

The excised clypeus and anterior margin of mentum is unusual in the Megasternini . Excised mentum is only known in the Central American genus Nitidulodes , which is also associated with aroid inflorescences ( Hansen 1991, Bloom et al. 2015). Excised clypeus is only present in Cycreon . Moreover, the strong variation of mentum and clypeus shape between different species of Cycreon is also unusual within Megasternini . Usually these characters are very similar in congeneric species and differ at most between genera. We suppose that this interspecific variation in Cycreon may indicate species-specific food and host-plant preferences. The data by Hoe et al. (2018) indicate some kind of specificity in host plants, which would be in agreement with this assumption. For example, various genera and species of Schismatoglottideae were sampled in Mulu National Park (Malaysia, Sarawak) from December 2017 to February 2018, but Cycreon beetles were only found in sampled species of Schismatoglottis (beetles were present in all sampled plants), whereas not a single specimen was found in inflorescences of Anadendrum, Aglaonema, Alocasia , Bucephalandra and Lasia . Additionally, the material collected from various inflorescences of the single aroid tribe Schismatoglottideae by Low et al. (2014, 2016), Hoe & Wong (2016) and Hoe et al. (2018) includes two very closely related subspecies only ( Cycreon floricola floricola and C. floricola borneanus ), despite consisting of more than 1000 specimens; not a single specimen of another Cycreon species was collected even in peninsular Malaysia, despite the sampled localities were close to those of two other species ( C. armandi and C. adolescens ). We suppose this may be caused by the focus on a single narrow group of host plants, and is congruent with the expected species-specific host preferences in Cycreon beetles.