Natural colours could be used as dye to identify Tribolium castaneum (Herbst) eggs.

Abstract

Identification of eggs in grain/flour is critical for managing stored grain pests. Chemical dyes, which are typically used to identify eggs, may irritate skin and eyes. The current study seeks to uncover naturally coloured materials that could be employed as natural stains to differentially colour Tribolium castaneum (Herbst) eggs from the grain. In the current research, the colour, pH, total phenolics, anthocyanin, and flavonoid content were measured in onion, beetroot, turmeric powder, black grapes, and teak leaves’ aqueous extracts. The highest anthocyanin concentration was found in turmeric extracts (1.55 mg equivalent of cyanidin-3-glucoside g−1), while the highest flavonoid level was found in teak extract (12.13 mg equivalent catechine g−1). Total phenols were highest in onion extract (5.03 mg gallic acid equivalent g−1). Beetroot and teak stains might readily colour the flour red and dark brown, respectively while leaving the eggs uncolored. Grape and onion stains gave a slight purplish and light pink colour to the eggs while remaining particles were dark violet and dark pink, respectively. Since the eggs and flour were both coloured yellow, the turmeric stain proved ineffective. Highest percentage of hatchability (80.99%) was observed in original grape extract treatment. Colour and pH of the extracts determined the ability of a natural dye to stain flour, keeping the eggs unstained. The hatched larvae from the stained eggs did not exhibit any morphological alteration, and their growth time was unchanged. These natural dyes are indeed cheap, easily procurable and innocuous and can be sustainable substitutes of chemical dyes.