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DNA-barcoding and DNA-based species delimitation are major tools in DNA taxonomy. Sampling has been a central debate in this context, because the geographical composition of samples affect the accuracy and performance of DNA-barcoding. Performance of complex DNA-based species delimitation is to be tested under simpler conditions in absence of geographic sampling bias. Here, we present an empirical data set sampled from a single locality in a Southeast-Asian biodiversity hotspot (Laos: Phou Pan mountain). We investigate the performance of various species delimitation approaches on a megadiverse assemblage of herbivore chafer beetles (Coleoptera: Scarabaeidae) to infer whether species delimitation suffers in the same way from exaggerate infraspecific variation despite the lack of geographic genetic variation that led to inconsistencies between entities from DNA-based and morphology-based species inference in previous studies. For this purpose, a 658 bp fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) was analysed for a total of 186 individuals of 56 morphospecies. Tree based and distance based species delimitation methods were used. All approaches showed a rather limited match ratio (max. 77%) with morphospecies. PTP and TCS prevailingly over-splitted morphospecies, while 3% clustering and ABGD also lumped several species into one entity. ABGD revealed the highest congruence between molecular operational taxonomic units (MOTUs) and morphospecies. Disagreements between morphospecies and MOTUs were discussed in the context of historically acquired geographic genetic differentiation, incomplete lineage sorting, and hybridization. The study once again highlights how important morphology still is in order to correctly interpret the results of molecular species delimitation.

The current paper gives an overview of the species of continental Asia so far assigned to the genus Microserica Brenske, 1894. Moronoserica Ahrens, Lukic & Liu, new genus, and Gastroserica (Helioserica Ahrens, Lukic & Liu, new subgenus), and 33 new species are described: Gastroserica bannok Ahrens, Lukic & Liu, new species, G. fumaria Ahrens, Lukic & Liu, new species, G. ivoi Ahrens, Lukic & Liu, new species, G. loei Ahrens, Lukic & Liu, new species, G. lucidomarginalis Ahrens, Lukic & Liu, new species, G. phukradung Ahrens, Lukic & Liu, new species, G. piceocoerulea Ahrens, Lukic & Liu, new species, G. rubropicea Ahrens, Lukic & Liu, new species, G. simaoensis Ahrens, Lukic & Liu, new species, G. yuebaensis Ahrens, Lukic & Liu, new species, Microserica allovarians Ahrens, Lukic & Liu, new species, Mic. banlaoana Ahrens, Lukic & Liu, new species, Mic. caiyangheana Ahrens, Lukic & Liu, new species, Mic. chaiyaphum Ahrens, Lukic & Liu, new species, Mic. cucphuong Ahrens, Lukic & Liu, new species, Mic. ferestictica Ahrens, Lukic & Liu, new species, Mic. hieroglyphica Ahrens, Lukic & Liu, new species, Mic. multipunctata Ahrens, Lukic & Liu, new species, Mic. namnao Ahrens, Lukic & Liu, new species, Mic. neosimplex Ahrens, Lukic & Liu, new species, Mic. parasimplex Ahrens, Lukic & Liu, new species, Mic. paravicula Ahrens, Lukic & Liu, new species, Mic. planiforceps Ahrens, Lukic & Liu, new species, Mic. viengvai Ahrens, Lukic & Liu, new species, Mic. vinden Ahrens, Lukic & Liu, new species, Mic. vipinglangensis Ahrens, Lukic & Liu, new species, Moronoserica banmethout Ahrens, Lukic & Liu, new species, Mor. renong Ahrens, Lukic & Liu, new species, Mor. squamulatoides Ahrens, Lukic & Liu, new species, Mor. songbae Ahrens, Lukic & Liu, new species, Mor. thungyai Ahrens, Lukic & Liu, new species, Oxyserica bifascipennis Ahrens, Lukic & Liu, new species, O. serena Ahrens, Lukic & Liu, new species. The revision results in 39 new combinations: Gastroserica bisignata (Nomura, 1974) new combination, G. cognata (Frey, 1972) new combination, G. dohertyi (Ahrens & Fabrizi, 2009) new combination, G. hiulca (Brenske, 1897) new combination, G. lucens (Ahrens & Fabrizi, 2009) new combination, G. nitidipyga (Nomura, 1974) new combination, G. quateorum (Frey, 1972) new combination, G. roingensis (Fabrizi & Ahrens, 2016) new combination, G. varians (Moser, 1915) new combination, Microserica avicula (Arrow, 1946) new combination, Mic. costisquamosa (Ahrens, Fabrizi & Liu, 2019) new combination, Mic. septemfoliata (Frey, 1972) new combination, Moronoserica banvaneue (Bohacz & Ahrens, 2020) new combination, Mor. crenatostriata (Ahrens, 2004) new combination, Mor. geberbauer (Ahrens, 2004) new combination, Mor. ginae (Bohacz & Ahrens, 2020) new combination, Mor. helferi (Bohacz & Ahrens, 2020) new combination, Mor. lineata (Moser, 1915) new combination, Mor. squamulata (Moser, 1915) new combination, Mor. tenasserimensis (Bohacz & Ahrens, 2020) new combination, Mor. ventrosa (Bohacz & Ahrens, 2020) new combination, Oxyserica arunensis (Ahrens, 1998) new combination, O. bhutanensis (Frey, 1975) new combination, O. cechovskyi (Ahrens, 1999) new combination, O. diversicornis (Moser, 1915) new combination, O. elegans (Frey, 1975) new combination, O. gandakiensis (Ahrens, 1998) new combination, O. hispidula (Frey, 1975) new combination, O. interrogator (Arrow, 1946) new combination, O. marginata (Brenske, 1896) new combination, O. martensi (Ahrens, 1998) new combination, O. myagdiana (Ahrens, 1998) new combination, O. nigropicta (Fairmaire, 1891) new combination, O. pedongensis (Ahrens, 1998) new combination, O. pruinosa (Hope, 1831) new combination, O. schawalleri (Ahrens, 1998) new combination, O. schulzei (Ahrens, 1998) new combination, O. steelei (Ahrens, 2004) new combination, O. truncata (Brenske, 1898) new combination. Lectotypes were designated of Microserica hiulca Brenske, 1897 and Serica nigropicta Fairmaire, 1891. A checklist and key to genera, species groups, and species is given, the diagnostic characters of the newly revised taxa and their distribution is illustrated.

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