Synchrotron-radiation computed tomography uncovers ecosystem functions of fly larvae in an Eocene forest

Abstract

We report a hitherto unprecedented diversity of fly larvae (Diptera) from Eocene Baltic amber and the use of these to address palaeo-ecosystem functions and processes in the surrounding forests. Fly larvae have been considered exceptionally rare by the research community and have, like most insect larvae, been deemed of limited utility owing to challenges in identification. Herein, however, using synchrotron-x-ray radiation CT (SR-µCT) allowed us to detect and identify dozens of fly larvae from Baltic amber, and to infer their ecological interactions. One particular piece of amber contains 56 fly larvae and apparent mammalian feces. This fossil is of great interest for our understanding of carbon cycling in the Eocene forest. The occurrence of such a large number of fly larvae on the fecal remains indicates an important role of flies in recycling organic matter in the Eocene forest, much as some larvae do today. Analysis of the fly palaeo-communities also allowed us to hypothesize a mechanism by which massive, geologically relevant deposits of amber were formed in the Baltic region. Scanning allowed us to identify seven larvae closely related to the extant Syrphidae, whose larvae inhabit nests of eusocial Hymenoptera, or, sometimes, flows of sap dripping from trees damaged by other burrowing insect larvae.

35 million-year-old solid-wood-borer beetle larvae support the idea of stressed Eocene amber forests

“…Some newly prepared volume renders of specimens of hoverfly larvae reported by Baranov et al (2021) are shown for background information (Fig. 1a-e).…”

“…More precisely, water stress of the resin-producing trees might have been the cause (Martínez-Delclòs et al 2004;Labandeira 2014;Seyfullah et al 2018), possibly mediated by drought, flood diseases, wildfires, or plant parasites (though the impact of plant parasites has been questioned: Peris et al 2016;Peris and Rust 2020; but see also Peris 2020 andPeris et al 2021). Baranov et al (2021) recently reported a large number of hoverfly larvae (Syrphidae) of the group Volucellini preserved in Baltic amber. These larvae resemble modern hoverfly larvae that co-occur with wood-borer moth larvae (Cossidae, Lepidoptera), feeding on the plant juices that seep after the moth larvae have damaged the plants (Speight 2010).…”

“…Other extant larvae of Volucellini are associated with nests of eusocial hymenopterans (Marshall 2012). Such hymenopterans are rare in ambers, making it unlikely that the fossil larvae of Volucellini had such a life style (Baranov et al 2021). Presumably, the hoverfly larvae represent an indirect indication of the presence of a specific type of plant parasites, namely wood-borer larvae in the Eocene amber forest; in fact, also larger abundances of them might be expected (see discussion in Baranov et al 2021).…”

“…Such hymenopterans are rare in ambers, making it unlikely that the fossil larvae of Volucellini had such a life style (Baranov et al 2021). Presumably, the hoverfly larvae represent an indirect indication of the presence of a specific type of plant parasites, namely wood-borer larvae in the Eocene amber forest; in fact, also larger abundances of them might be expected (see discussion in Baranov et al 2021). Although in the modern fauna these seem mostly wood-borer larvae of the group Lepidoptera, also other types of wood-borer larvae could be expected to cooccur with the hoverfly larvae.…”

Expanding the Record of Larvae of False Flower Beetles With Prominent Terminal Ends

“…Their original habitat is clearly close enough to the source of tree resin to have the larvae trapped in it to become fossilised as amber inclusions. Again, it ap-pears that the so far seeming rarity of these larvae is only an effect of not reporting such larvae, despite their principal availability (see Baranov et al 2020Baranov et al , 2021.…”