Native Fluorescence from Juvenile Stages of Common Food Storage Insects

Insect infestation of stored foods has significant economic and health consequences; the development of novel methods of detection thus presents considerable opportunities. The fluorescence from nine species of storage insects (beetles and moths) was studied; the juvenile stages of all nine species exhibited fluorescence under long-wave (365 nm) UV light; none of the adult insects emit fluorescence, so the fluorophore(s) might be a compound(s) associated with the unsclerotized cuticle. The spectra of larval stages of Ephestia kuehniella, Oryzaephilus surinamensis, Corcyra cepahlonica, Tribolium castaneum, and Tribolium confusum exhibited excitation maxima in the range from 345 to 350 nm and emission maxima in the range from 421 to 427 nm, suggesting that fluorescence arises from a common chromophore; similarities in fluorescence properties implicate one of the many pteridine ring-containing compounds (pterins) commonly found in insects. Larvae and even eggs were readily imaged on foods using fluorescence under 365-nm excitation. Fluorescence thus appears to be ubiquitous in immature food storage insects, and fluorescence detection may be useful as a general method to detect insects in foods and agricultural commodities during storage or processing. Keywords: Fluorescence; storage insects; eggs; larvae; pupae; cuticle; stored products