Comparison of new castor (Ricinus communis L.) genotypes in the mediterranean area and possible valorization of residual biomass for insect rearing

Despite its high suitability to European climates and a considerable commercial-grade for industrial applications (about 25% of global castor oil production is processed in EU), castor crop is inexistent in the European farming systems. The revival of castor in Europe could result in an attractive opportunity not only for the production of domestic oil, but also for potential strategic uses of residual biomass at harvest in the bio-based economy. In the light of the recent inclusion of insect-derived products in the list of “Novel Food” (EC 16/11/2015), a very interesting use of castor leaves is for feeding eri silkworm (Samia cynthia ricini), a wild moth able to produce textile fiber from the cocoon, as well as to accumulate interesting oil and protein amounts in the pupae. Two screening trials comparing four different castor hybrids were set in Bologna (Italy) and Aliartos (Greece) in 2015; moreover, two of them, contrasting for the morphological habitus, were tested in Bologna to set up artificial diets for rearing eri silkworms. The artificial diets were prepared starting from both green (GADiet) or senescent leaves (SADiet), and the insect rearing performance was evaluated in comparison to a standard rearing on fresh leaves (FCLeaf). Castor hybrids demonstrated to be well adapted to both Mediterranean environments. More favorable temperatures and regular irrigation led to significantly better productive performance in Greece (up to 54% oil yield): higher biomass accumulation, increased seed yield (+34%) and seed oil content (+9%), even though the best hybrids were found the same in the two environments. The performance of the artificial diets in eri silkworm rearing was inferior compared to the fresh castor leaves, but the majority of the larvae fed with artificial diets (∼85% of total, on average of the two artificial diets) was anyhow able to complete the development until the cocoon spinning. The administration of artificial diets caused higher mortality, a general elongation of the duration of larval stage (30 d for SADiet > 24 d for GADiet > 17 d for FCLeaf), and a reduced cocoon weight. The fatty acid composition of lipid extracted from the pupae was also significantly influenced by the rearing diet, with FCLeaf fed silkworms accumulating more linolenic acid compared to those fed on artificial diets. In conclusion, castor plant showed satisfactory seed yields in both Mediterranean locations; the use of senescent leaves to set up an artificial diet to rear eri silkworms for bio-based applications resulted a promising and affordable route for valorizing residual biomass under the biorefinery concept.