Chemical evaluation of the Rhynchophorus ferrugineus larvae fed on different substrates as human food source.

We investigated the chemical composition of the weevil Rhynchophorus ferrugineus larvae, traditionally used as human food in Asia and known worldwide as one of the most significant pest for palm trees. Total fat content and fatty acid composition were analyzed using standard methodologies in (1) weevil larvae reared on apple fruit slices and wild specimens collected from attacked (2) Phoenix canariensis and (3) Syagrus romanzoffiana palm trees. Total fat content was extremely high in all the specimens (ranged between 57.62 and 60.03% based on dry weight). Despite sharing the same prevalent fatty acids (myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, α-linoleic acid, and α-linolenic acid), fatty acid composition of the wild weevil larvae significantly differed from that of the specimens raised on apple fruit, due to the presence of other minor compounds. In general, a good balance between unsaturated fatty acids (∼53.68% of total fatty acids) and saturated fatty acids (∼43.41% of total fatty acids) and a low cholesterol content (74.61-152.32 mg/kg based on dry matter) were detected in all the specimens. Conversely, the weevil larvae did not represent a good source of α-tocopherol (14.17-26.22 mg/kg based on dry matter). The ability of the protein extracts obtained from the weevil larvae to inhibit in vitro the angiotensin-converting enzyme, the main enzyme involved in blood pressure regulation, was also investigated. To simulate gastrointestinal digestion process, protein extracts were hydrolyzed by the gastrointestinal enzymes. A significantly lower IC50 (0.588-0.623 mg/ml) was measured in all the protein extracts after enzymatic hydrolysis versus the corresponding crude protein extracts (3.270-3.752 mg/ml). Given that the weevil larvae are able to provide interesting benefits for human health, this study supports their use as human food not just in the native countries where they are traditionally consumed and farmed but also throughout the world.

Effects of the diet on the microbiota of the red palm weevil (Coleoptera: Dryophthoridae).

Rhynchophorus ferrugineus, also known as the red palm weevil, is regarded as the major pest of palm trees. Although studies of the microbiota associated with this species have been performed in recent years, little attention has been dedicated to the influence of the diet in shaping the host bacterial community. Here, we investigated the influence of food sources (i.e. palm tissues vs apple based substrate) on the microbial diversity associated with RPW, which was compared with the microbiota associated with wild individuals of the sister species Rhynchophorus vulneratus. The bacterial characterization was performed using a culture independent approach, i.e. the 16S rRNA pyrotag, and a culture dependent approach for a subset of the samples, in order to obtain bacterial isolates from RPW tissues. The bacterial community appeared significantly influenced by diet. Proteobacteria resulted to be the most abundant clade and was present in all the specimens of the three examined weevil groups. Within Proteobacteria, Enterobacteriaceae were identified in all the organs analysed, including hemolymph and reproductive organs. The apple-fed RPWs and the wild R. vulneratus showed a second dominant taxon within Firmicutes that was scarcely present in the microbiota associated with palm-fed RPWs. A comparative analysis on the bacteria associated with the palm tissues highlighted that 12 bacterial genera out of the 13 identified in the plant tissues were also present in weevils, thus indicating that palm tissues may present a source for bacterial acquisition.