Developmental stages of the hooded beetle Sericoderus lateralis (Coleoptera: Corylophidae) with comments on the phylogenetic position and effects of miniaturization

The first detailed morphological study of larvae, pupae and adults of a species of the hooded beetles (Coleoptera: Corylophidae) – Sericoderus lateralis – is presented. Histological sectioning, scanning and transmission electron microscopy, laser confocal microscopy and 3D-computer reconstruction were used. For the first time we report that according to the morphometric data of S. lateralis, at least some corylophid beetles have three larval stages. A phylogenetic position of Corylophidae within a cucujoid-cleroid clade is confirmed, and also the placement of Sericoderini within a corlyophid subgroup, which does not include Periptycinae and Foadiini. The larvae of Sericoderus are mainly characterized by plesiomorphic features compared to those of other corylophid tribes, notably Peltinodini and Rypobiini. Morphological and developmental consequences of miniaturization are discussed. Corylophid beetles display much less specific and far-reaching morphological consequences of miniaturization compared to Ptiliidae. We report the presence of unique modifications in the neural system not shared with any other insects, such as a distinctly asymmetric supraoesophageal ganglion in first instar larva, and a total displacement of the brain to the thorax in the adult stage. A highly unusual feature of the digestive tract is the sclerotised, V-shaped ventral wall of the pharynx. Developmental and size dependent changes in the relative volume of different organs are addressed. All organ systems change allometrically in the development of S. lateralis. Allometric trends in the volume of organs confirm that the factors limiting miniaturization are the size of the neural system, associated with the number and size of neurons (most critical for first instar larva), the mass of the skeleton, the egg size, and consequently the volume of the reproductive system (for free-living insects).