Tijdschrift voor Entomologie 160 (2017) 89–138 An initial survey of aquatic and semi-aquatic Heteroptera (Insecta) from the Cardamom Mountains and adjacent uplands of southwestern Cambodia, with descriptions of four new species Dan A. Polhemus Previous collections of aquatic Heteroptera from Cambodia have been limited, and the biota of the country has remained essentially undocumented until the past several years. Recent surveys of aquatic Heteroptera in the Cardamom Mountains and adjacent Kirirom and Bokor plateaus of southwestern Cambodia, coupled with previous literature records, demonstrate that 11 families, 35 genera, and 68 species of water bugs occur in this area. These collections include 13 genus records and 37 species records newly listed for the country of Cambodia. The following four new species are described based on these recent surveys: Amemboa cambodiana n. sp. (Gerridae); Microvelia penglyi n. sp., Microvelia setifera n. sp. and Microvelia bokor n. sp. (all Veliidae). Based on an updated checklist provided herein, the aquatic Heteroptera biota of Cambodia as currently known consists of 78 species, and has an endemism rate of 7.7%, although these numbers should be considered provisional pending further sampling. Keywords: Heteroptera; Cambodia; water bugs; new species; new records Dan A. Polhemus, Department of Natural Sciences, Bishop Museum, 1525 Bernice Street, Honolulu, HI 96817 USA. [email protected] Introduction of collections or species records from the country in Aquatic and semi-aquatic Heteroptera, commonly the period preceding World War II. Following that known as water bugs, are a group of worldwide dis- war, the country’s traumatic social and political his- tribution with a well-developed base of taxonomy. As tory left it isolated until the 1990s, and therefore such, they have proven to be a useful entomological unvisited by collectors. Despite a renewed interest component for biodiversity surveys in many parts of in the survey of aquatic Heteroptera in neighbor- the world. This paper provides the results of targeted ing countries, such as Thailand and Vietnam, from collections of this group in the Cardamom Moun- the mid-1980s onward, Cambodia continued to re- tains area of southwestern Cambodia. The paucity main overlooked and unvisited, in part because of of previous work is illustrated by the fact that of the the hazards involved with the numerous land mines 78 species listed in this paper, 37 represent new and that had been planted throughout the country. Only previously unpublished records for the country. in 2017 was a first preliminary checklist of aquatic The aquatic Heteroptera biota of Cambodia re- Heteroptera published for the country, containing mained essentially un-sampled until the last several records of 41 species, based primarily on collec- years. In contrast to other French colonial possessions tions from nine widely scattered localities (Zettel in Indochina, there seems to be no documentation et al. 2017). By contrast, the current report, although Tijdschrift voor Entomologie 160: 89–138, Appendices 1–2, Figs 1–58. [ISSN 0040-7496]. brill.com/tve © Nederlandse Entomologische Vereniging. Published by Koninklijke Brill NV, Leiden. Published 15 December 2017. DOI 10.1163/22119434-00002068 Downloaded from Brill.com10/07/2021 06:11:13PM via free access <UN> 90 Tijdschrift voor Entomologie, volume 160, 2017 limited to the Cardamom Mountains and adjacent plateaus that extend progressively to the southeast highlands in the southwestern third of Cambodia, (Fig. 1); these latter two plateaus are also referred represents a more targeted and comprehensive set of to as the Elephant Mountains. All these areas were aquatic Heteroptera collections from 27 more geo- sampled in the course of the present surveys. graphically proximal localities. The Cardamom Mountains lie in southwestern Cambodia, south of the Tonle Sap basin, and west of the Mekong River. The overall form of the uplift Description of study area is that of a sandstone cuesta, dipping to the south- Although the central portion of Cambodia is com- west, and breaking to the northeast. The mountain posed of extensive lowlands that border the Mekong slopes are for the most part gentle, and the summit River and its tributary Tonle Sap river and lake sys- ridges of relatively even height, with the highest el- tem, the country also contains various upland areas. evations being Phnom Samkos at 1,717 m, Phnom These include the narrow and elongate Dangrek Tumpor at 1,516 m, and Phnom Kmoch at 1,220 m. Range that forms the border with Thailand along the Although sometimes also considered as part of the margin of the Khorat Plateau in Oddar Meanchey Cardamom Mountains, the 1813 m Phnom Aural and Preay Vihear Provinces; the southern terminus massif to the northeast is of completely different geo- of the Annamite Mountains that extend into the Vi- logical origin, and is topographically separated from rachey National Park area of Ratnakiri Province in the Cardomom uplift by an intervening lowland bar- the far northeast; a western extension of the basalt rier; as such, is in not considered as part of the Car- plateaus typical of the Vietnamese Central High- damom Mountains for the purposes of this report. lands which extend into the eastern Mondulkiri The Cardamom Mountains also continue westward Province; and the extensive Cardamom Mountain some distance into Thailand, and isolated outliers of uplift that occupies the southwest quarter of the the uplift also form offshore islands in the Gulf of country, primarily in the provinces of Pursat, Koh Thailand, such as Phu Quoc Island, which is admin- Kong, Kampong Speu, Kampot and Sihanoukville. istered by Vietnam. It is this latter Cardamom uplift that was the focus Aquatic insect diversity is influenced by stream of the current study. The Cardamom uplift is com- bed profile and composition, which is in turn in- posed of three major geomorphological units that lie fluenced by regional geology. Although a number of along the western margin of the Kampot Fold Belt studies have examined the overall tectonic setting of (Fyhn et al. 2016), and are separated by interven- Indochina, local field geology remains poorly con- ing gaps below 250 m elevation: the Cardamom strained, and published geological maps are often Mountains themselves, and the Kirirom and Bokor inaccurate. As such, the discussion below is based Fig. 1. View to the southeast from a high point on the Kirirom Plateau at 715 m elevation, showing typical topog- raphy and vegetation of the southwestern Cambodian highlands. The forest in the foreground on the left side of the valley is dominated by Tenassarim pine (Pinus merkusii), while the forest on the right side of the valley is a wetter semi-deciduous broadleaf forest. The blue ridge in the distance is the Elephant Mountains, terminating in the Bokor Plateau visible in the left-central portion of the uplift, and supporting montane evergreen broadleaf rainforest. Downloaded from Brill.com10/07/2021 06:11:13PM via free access <UN> D. A. Polhemus: Cambodian Aquatic Heteroptera 91 largely on mining company and NGO reports (Save Sap lake and river system may be a graben (a down- Cambodia’s Wildlife 2006; Earth Worx 2009; JICA ward-dropped fault block) lying between the elevat- 2010). Based on these sources, the surface geology ed Mesozoic sandstone exposures of the Cardamom of the Cardomom Mountains in the areas covered Mountains and eastern Thailand respectively (Run- during the current survey consists of Mesozoic del 1999). Whatever its original mode of genesis, the sandstone formations of Triassic to Cretaceous age Tonle Sap basin is now infilled with Quaternary to with interbedded conglomerates, shales, evaporites recent sediments, many of them sandy and derived and coal measures, all formed in continental mar- from the bordering mountains. Rivers traversing the gin or shallow-water marine environments. These lowlands between the Cardamom Mountains and sandstones appear to be correlative with those of the lake, such as the Bori Bo River sampled dur- the Khorat Plateau of eastern Thailand (Fyhn et al. ing this study, thus tend to be shallow and braided, 2010, 2016), and although the stratigraphy and pe- occupying broad, sandy, unshaded beds, and support trology of the Thai formations have been described aquatic insect species assemblages different from in detail by LaMoreaux et al. (1958), no similarly de- those seen in the rocky mountain foothills. tailed treatment is currently available for Cambodia. The Mesozoic sandstones of Cambodia have also Based on the work of LaMoreaux et al. (1958), and been partially eroded, creating many small windows mining company reconnaissance, the Cambodian which reveal the underlying Palaeozoic basement sandstones as a whole consist of a lower Triassic se- rocks, consisting of metamorphic and granitic forma- quence that is moderately folded and forms subdued tions (Earth Worx 2009). These basement rocks are topography, unconformably overlain by a Jurassic more broadly exposed in the northwestern section to Cretaceous sequence that is only gently folded of the Cardamom uplift. The Mesozoic sandstones (Earth Worx 2009). In eastern Thailand the upper have also been intruded at various points by small sequence is generally horizontal and forms large, to medium-sized dioritic to granitic plugs. Most of flat-topped, mesa-like hills, while in the Cardamom these intrusive bodies have large, irregular hornfels Mountains this sequence is tilted, dipping to the halos created by contact metamorphosis. In some southwest toward the Gulf of Thailand. The older cases hornfels areas without apparent intrusives in- Triassic sandstone series is not extensively exposed in dicate the presence of plugs at a shallow depth below the Cardamom Mountains, but does crop out at the the current erosion surface. Because geological maps northwestern end of the range, and in small areas of Cambodia are incomplete at a local scale, there at the eastern end of the north slope as well (Save are often many more of these small-sized intrusive Cambodia’s Wildlife 2006).