2.1. Study group, sampling, and identification

The study group is the megadiverse tribe Sericini that contains worldwide nearly 4,000 described species in about 200 genera (Ahrens, 2006). They are one of the oldest lineages of phytophagous Scarabaeidae and diversified with the rise of the angiosperms 108 Ma (Ahrens et al., 2014; Eberle et al., 2017). Sericini are nearly worldwide distributed, except in Australia, most oceanic islands, archipelagos, and circumpolar regions (Ahrens, 2006). The polyphagous herbivore adults are fully winged while larvae feed on roots and underground stems of living plants (Ritcher, 1966). Some species are considered as crop pests (Nair, 1986). Their highly similar external morphology makes the species difficult to distinguish, but highly complex male genitalia are well‐differentiated between species and show only little intraspecific variation (Ahrens & Lago, 2008).

Sampling was conducted during 4 weeks in April 2014 by Carolus Holzschuh and local collectors in the Phou Pan mountain area (Laos, Hua Phan province) (Figure 1) (ca. 20°12′N, 104°01′E), at an elevation between 1,300 and 2,000 m. Specimens were collected using light traps, by hand, or netting during daytime. The Phou Pan mountain is situated in the Indo‐Burmese biodiversity hotspot area (Myers et al., 2000) which is characterized by extremely high endemism. The habitat with its dense rainforests (Müller et al., 2013) offers a large variety of plant species for herbivore insects to feed on. For this study, we used only males (1,086 specimens), since they were assignable to distinct morphospecies, while females are often not distinguishable among closely related syntopically occurring species. Samples were pinned after DNA extraction, dry mounted, labeled, and preserved at the ZFMK (Zoologisches Forschungsmuseum Alexander König, Bonn, Germany) (see Table S1).

Collecting area in Laos (20°12′N, 104°01′E) (marked with a black dot)

Specimens were presorted to morphospecies using the complex shape of their copulation organ, that is, aedeagus, which has been proven to be the best suited trait system to robustly infer species entities for this group (Dalstein et al., 2019; Eberle et al., 2016). For this purpose, male genitalia of all specimens were dissected. Habitus and genitalia of each species were photographed with a stereomicroscope (ZEISS Stereo Discovery.V20) connected to a ZEISS Axiocam. Presumably undescribed species that were not yet referable to an available species name were numbered consecutively (sp1, sp2, etc.).