Application of confocal laser scanning microscopy for the study of microarthropods: A case study of eriophyoid mites (Acari, Eriophyoidea)

Capturing autofluorescence (natural emission of light by biological structures when they have absorbed light) or/and emitted light of specific fluorophores (after staining an animal with fluorescent dyes) is one of the approaches to study morphology and anatomy. The cuticle of many arthropods exhibits a strong autofluorescence signal, which makes them highly suitable for CLSM without additional staining. As a result various microarthropods (small crustaceans, proturans, beetles, coccids, mites, ticks etc., including those embedded in ancient amber) can be successfully studied using CLSM techniques. An important advantage of CLSM is that it enables surface reconstructions of the samples embedded in permanent slides from collections, including rare and/or old type slides which are not possible for recollecting and thus not available for SEM study.

Eriophyoid mites is a group of highly simplified phytoparasites, we usually mount them in Hoyer or modified Berlese medium and study under high magnification using conventional light microscope equipped with DIC or phase contrast. Recent studies show that capturing autoflourescence of eriophyoids mounted in simple Hoyer allows: #1 reconstructing topography of exoskeleton (including volumetric representation of the prodorsal shield ornamentation and other important diagnostic characters) and easy graphical comparison/representation of morphological variability which is crucial for correct ID; #2 studying topography of cuticle-lined (of totally cleared specimens) and soft (of partially cleared specimens) internal genital organs; #3 precise reconstruction of tiny internal apodemes and measuring morphometrics (mostly lengths and angles extracted from CLSM images) which can be used for statistical comparison, 3D modeling, separating and rediagnosing problematic taxa.

Many fundamental aspects, such as histology, anatomy and embryology of eriophyoids (and most other groups of mites) are greatly unexplored. Immunofluorescence technique combined with confocal microscopy has been widely used for studying cells and tissues of various organisms but still rarely used in acarology. Recently genital musculature of eriophyoids has been studied based on specimens stained with TRITC-phalloidin. Further investigations of eriophyoids using fluorescent stains will obviously result in obtaining new data (first of all on anatomy of musculature, nervous system and early development) which will be important for comparative and phylogenetic studies.