Palaeoentomology 004 (4): 390–404 ISSN 2624-2826 (print edition) https://www.mapress.com/j/pe/ PALAEOENTOMOLOGY Copyright © 2021 Magnolia Press Article ISSN 2624-2834 (online edition) PE https://doi.org/10.11646/palaeoentomology.4.4.14 http://zoobank.org/urn:lsid:zoobank.org:pub:9F96DA9A-E2F3-466A-A623-0D1D6689D345 The earliest record of fossil solid-wood-borer larvae—immature beetles in 99 million-year-old Myanmar amber CAROLIN HAUG1, 2, *, GIDEON T. HAUG1, ANA ZIPPEL1, SERITA VAN DER WAL1 & JOACHIM T. HAUG1, 2 1Ludwig-Maximilians-Universität München, Biocenter, Großhaderner Str. 2, 82152 Planegg-Martinsried, Germany 2GeoBio-Center at LMU, Richard-Wagner-Str. 10, 80333 München, Germany �[email protected]; https://orcid.org/0000-0001-9208-4229 �[email protected]; https://orcid.org/0000-0002-6963-5982 �[email protected]; https://orcid.org/0000-0002-6509-4445 �[email protected] https://orcid.org/0000-0002-7426-8777 �[email protected]; https://orcid.org/0000-0001-8254-8472 *Corresponding author Abstract different plants, including agriculturally important ones (e.g., Potts et al., 2010; Powney et al., 2019). On the Interactions between animals and plants represent an other hand, many representatives exploit different parts of important driver of evolution. Especially the group Insecta plants, often causing severe damage up to the loss of entire has an enormous impact on plants, e.g., by consuming them. crops (e.g., Metcalf, 1996; Evans et al., 2007; Oliveira et Among beetles, the larvae of different groups (Buprestidae, Cerambycidae, partly Eucnemidae) bore into wood and are al., 2014). Especially some groups of beetles (Coleoptera) therefore called wood-borer larvae or borers. While adults of are known for their phytophagous behaviour, with some these beetle groups are well known in the fossil record, there of these even having large economic impacts (e.g., bark are barely any fossils of the corresponding larvae. We report beetles; Kirkendall et al., 2015 and references therein). here four new wood-borer larvae from Cretaceous Kachin One such beetle group is Buprestidae. The about amber (Myanmar, ca. 99 Ma). To compare these fossils 15,000 formally described extant species of this group with extant wood-borer larvae, we reconstructed the body (Bellamy, 2008–2009) are collectively known as jewel outline and performed shape analysis via elliptic Fourier transformation and a subsequent principal component beetles or metallic wood-boring beetles. As these names analysis. Two of the new larvae plot closely together suggest, the adults stand out by their shiny and metallic and clearly in the same area as modern representatives appearance, while they otherwise look like more common of Buprestidae. As they furthermore lack legs, they are beetles. Larvae, also known as flatheaded borers, resemble interpreted as representatives of Buprestidae. The other two grubs at first sight, but differ in several aspects (e.g., Wu new larvae possess legs and plot far apart from each other. et al., 2017). The head is very indistinct, immersed into They are more difficult to interpret; they may represent larvae the wide thorax region, which lacks legs. The abdomen of early offshoots of either Cerambycidae or Buprestidae, which still retain longer legs. These findings represent the exhibits segmentation, but otherwise appears worm- earliest fossil record of larvae of Buprestidae and possibly of shaped (vermiform). The larvae can reach astonishing Cerambycidae known to date. sizes of more than 100 mm (Bellamy & Volkovitsh, 2005). They bore through different parts of plants, like roots, Keywords: Buprestidae, Cerambycidae, Burmese amber, stems and leaves, fulfilling their eponymous ecological Cretaceous, Kachin amber role as plant-borers. Overall, the larvae are very distinct, only very few larvae of other groups have a comparable morphology. Introduction About 35,000 extant species of Cerambycidae, longhorn beetles, have been formally described (Svacha The interaction between plants and animals is an important & Lawrence, 2014). Adults possess the eponymous and driving force of evolution. This is especially true for characteristic very long antennae. The larvae, called representatives of the group Insecta, such as butterflies, roundheaded borers, feed on plant material, very similar beetles, or bees (e.g., Kergoat et al., 2017). On the one to those of Buprestidae. Morphologically, certain larvae hand, many representatives are important pollinators of of Cerambycidae also closely resemble the latter, mainly 390 Submitted: 16 Aug. 2021; accepted by D.-Y. Huang: 26 Aug. 2021; published: 31 Aug. 2021 Licensed under Creative Commons Attribution-N.C. 4.0 International https://creativecommons.org/licenses/by-nc/4.0/ differing in the transition area between thorax and Material and methods abdomen: while the thorax is distinctly set off from the abdomen in larvae of Buprestidae, this transition is less Material pronounced in those of Cerambycidae (e.g., Wu et al., Four fossil specimens from the Palaeo-Evo-Devo 2017). Research Group Collection of Arthropods, Ludwig- Of Eucnemidae, false click beetles, there are about Maximilians-Universität München are reported here (PED 1,500 formally described extant species (Muona, 2010). 0597, 0816, 0838, 1130). All are preserved in Kachin The adults are usually brown to black with often serrate or amber (Cretaceous, ca. 99 Ma) from the Hukawng Valley, more or less comb-shaped antennae. Also here, the larvae Myanmar (Cruickshank & Ko, 2003; Shi et al., 2012; Yu feed on plant material as in the previous two groups, but et al., 2019). The specimens were legally acquired via the only few can bore into wood. Such larvae of Eucnemidae internet platform ebay.com from the fossil trader burmite- also morphologically resemble those of Buprestidae, but miner. possess outward curved mandibles (e.g., Muona, 2010). One extant larval specimen of Buprestidae from the Adult jewel beetles are well represented in the fossil entomological collections of the Centrum für Naturkunde record, with about 100 formally described species in the (CeNak) Hamburg (ZMH 62921) is included for literature (Pan et al., 2011), the oldest one being of Middle Jurassic age (168–166 Ma; Alexeev, 1999). The fossil comparison. record of adult longhorn beetles is rich (see Discussion), the oldest record probably being from the Late Jurassic Documentation methods (ca. 150 Ma; Münster in Germar, 1839). Of false click Fossil specimens were documented on a Keyence VHX- beetles, more than 60 formally described fossil species 6000 digital microscope. Specimens were documented are known (Li et al., 2021), with the oldest record from in front of different backgrounds (black and white) the Late Jurassic (ca. 151 Ma; Oberprieler et al., 2016). and different light settings (cross-polarised coaxial In contrast to the fossil record of adult representatives, light, unpolarised ring light) (Haug & Haug, 2019). the fossil record of the larvae is much scarcer. Only one Combinations with the best contrast were chosen for fossil larva of false click beetles is known (Chang et al., presentation. 2016; Early Cretaceous, ~125 Ma, see Swisher et al., All images were recorded as composite images 1999). Some larvae of false click beetles are known to (Haug et al., 2008; Kerp & Bomfleur, 2011). To overcome be solid-wood borers (solid-wood-boring types of Muona limitations of dept of field, stacks of images with & Teräväinen, 2020: fig. 6), morphologically resembling varying focus levels (frame) were recorded and fused larvae of jewel beetles. Yet, most larvae of false click to sharp images with the built-in software. To overcome beetles feed on fungi in soft rotten wood and do not form limitations of field of view, several adjacent image details galleries (Muona, 2010: 62), hence, cannot be considered were recorded and merged to a panorama with the built- solid-wood borers. The fossil described by Chang in software. To avoid overexposed or underexposed areas et al. (2016) is of this latter, vermiform, presumably each frame was recorded with HDR (see Haug et al., 2013). non-solid-wood-boring type. Even older wood-boring For one close-up, a stack was recorded and processed in larvae, namely of the group Micromalthidae, have been FIJI, generally following the method described in Haug et reported from Lebanese amber (Kirejtshuk & Azar, al. (2009). 2008). Similar to many larvae of Eucnemidae, these The extant specimen was documented via larvae live in rotten, hence softer wood (e.g., Pollock macrophotography with a Canon Rebel T3i digital camera & Normark, 2002; Normark, 2013; Hörnschemeyer, and a Canon MP-E 65 mm macro lens equipped with a 2016; Perotti et al., 2016). Few fossil larvae of longhorn polarisation filter. A Yongnuo YN24EX E-TTL twin flash beetles have been mentioned, fewer have been figured, or two Yongnuo Digital Speedlite YN560EX II flashes e.g., one in Baltic amber (Eocene, ca. 38 Ma; Bachofen- Echt, 1949: 115, fig. 102; Gröhn, 2015: 272). Only one with polarisation filters perpendicular to that on the lens larval jewel beetle seems to have been figured so far were used to illuminate the specimen. The specimen was (New Jersey amber, ca. 90 Ma; Grimaldi & Engel, 2005: documented in 70% ethanol; hence the cross-polarised 381, fig. 10.36), and few cases in Baltic amber have light was necessary to reduce reflections (e.g., Haug et al., been mentioned (Spahr, 1981 and references therein). 2011). As for