Agricultural by-products from Greece as feed for yellow mealworm larvae: circular economy at a local level

Organic side-streams and agricultural wastes represent a big pool of untapped and underrated resources which could be efficiently exploited for insect rearing. We evaluated the suitability of eleven agricultural by-products, stemming from the production of cotton, sugar beet, sunflower, barley, oats, peas and vetch, for the development of larvae of the yellow mealworm, Tenebrio molitor. In a first bioassay, by-products were screened singly to evaluate their potential to support the development of middle sized (4th-6th instar) larvae. In a second bioassay, by-products were supplemented with carrot, and their potential to support complete larval development (first instar until first pupation) was evaluated. Lastly, a third bioassay was conducted in which the more promising by-products were used as components of isonitrogenous diets for middle sized larvae, at two nitrogen levels (2.7 and 3.2%). Our results show the suitability of several agricultural by-products from Greece for T. molitor larvae. The best results though were obtained with the oat and the barley by-product (class II), tested either singly or mixed in diets. These by-products can be utilised singly or in composed diets and can greatly decrease the feed costs of mealworm production. Moreover, the results obtained from the isonitrogenous diets bioassay, show that besides nitrogen content, other factors need to be considered when formulating optimal diets. Our study aims to implement circular economy practices in insect farming at a local level.