Autofluorescent Biomolecules in Diptera: From Structure to Metabolism and Behavior

Abstract

Light-based phenomena in insects have long attracted researchers’ attention. Surface color distribution patterns are commonly used for taxonomical purposes, while optically-active structures from Coleoptera cuticle or Lepidoptera wings have inspired technological applications, such as biosensors and energy accumulation devices. In Diptera, besides optically-based phenomena, biomolecules able to fluoresce can act as markers of bio-metabolic, structural and behavioral features. Resilin or chitinous compounds, with their respective blue or green-to-red autofluorescence (AF), are commonly related to biomechanical and structural properties, helpful to clarify the mechanisms underlying substrate adhesion of ectoparasites’ leg appendages, or the antennal abilities in tuning sound detection. Metarhodopsin, a red fluorescing photoproduct of rhodopsin, allows to investigate visual mechanisms, whereas NAD(P)H and flavins, commonly relatable to energy metabolism, favor the investigation of sperm vitality. Lipofuscins are AF biomarkers of aging, as well as pteridines, which, similarly to kynurenines, are also exploited in metabolic investigations. Beside the knowledge available in Drosophila melanogaster, a widely used model to study also human disorder and disease mechanisms, here we review optically-based studies in other dipteran species, including mosquitoes and fruit flies, discussing future perspectives for targeted studies with various practical applications, including pest and vector control.

Imaging and spectral analysis of autofluorescence patterns in larval head structures of mosquito vectors

“…[1][2][3][4][5] Autofluorescence (AF) emission, in particular, has been mainly characterized in butterfly pigments and in resilin-enriched and chitinous body structures from different insect orders, including Diptera, providing a valuable basis for various label-free morphological, taxonomic, and functional studies. [6][7][8][9][10][11][12][13] The optical-based investigation of the scattering properties of mosquito adults allowed to obtain promising data for sex-and species-specific detection in the field for vector surveillance. Indeed, a recently developed system based on the spectral and polarization properties of the mosquito body, integrating wing-beat frequency analysis, was shown to have the potential to optically discriminate individuals and sexes of Anopheles coluzzii Coetzee & Wilkerson, 2013 and An.…”

“…38,41,[43][44][45][46][47][48] Up to now, only a few studies have focused on the characterization of AF in dipteran larvae. 13 For instance, AF emission signal detected as an overall broadband or as bands at increasing wavelengths along the visible spectrum has been applied to recognize morphological structures and organs to support comparative, taxonomic, developmental and physiological studies. 49,50 The detection of AF of defined endogenous fluorophores has been specifically used in metabolic studies.…”

“…The bluish AF of the elastic and resilient resilin allows also its differentiation from stiffer chitinous materials, fluorescing in the yellowish-to-reddish spectral region. 9,13,54 Currently, investigations on the AF of compounds with a biomechanical function have been limited to the adult stage. 13,15,17 In the case of mosquito larvae, behavioral differences across species have been assessed in terms of locomotion, arresting, browsing and filtering in response to physical and food-related environmental stimuli.…”

“…9,13,54 Currently, investigations on the AF of compounds with a biomechanical function have been limited to the adult stage. 13,15,17 In the case of mosquito larvae, behavioral differences across species have been assessed in terms of locomotion, arresting, browsing and filtering in response to physical and food-related environmental stimuli. 35 Instead, information on the structural and biomechanical properties of sensory organs and surrounding tissues that can potentially modulate sensory inputs 55 is currently lacking.…”

“…The bluish AF of the elastic and resilient resilin allows also its differentiation from stiffer chitinous materials, fluorescing in the yellowish-to-reddish spectral region. 9 , 13 , 54 Currently, investigations on the AF of compounds with a biomechanical function have been limited to the adult stage. 13 , 15 , 17 …”