Antibacterial Activity of Extracts from Seven Insect Species Against Mediterranean Marine Aquaculture Bacterial Pathogens

Beyond their role as fishmeal replacements in aquafeeds, insects may enhance fish resistance to microbial diseases and improve feed shelf life through the presence of antibacterial compounds. This study evaluated the antibacterial activity of extracts from silkworm pupae (Bombyx mori, BM), larval meals of black soldier fly (Hermetia illucens, HI), mealworm (Tenebrio molitor, TM), and superworm (Zophobas morio, ZM), and adults of house cricket (Acheta domesticus, AD), two-spotted cricket (Gryllus bimaculatus, GB) and weaver ant (Oecophylla smaragdina, OS). The extracts were tested against ten Gram-negative marine bacterial pathogens associated with aquaculture disease outbreaks, as well as the Gram-positive bacterium, Bacillus thuringiensis. The antibacterial activity of aqueous and solvent-soluble extracts was assessed using agar diffusion assays, turbidimetric growth kinetics, and MTT metabolic assays. Several insect extracts exhibited moderate to strong antibacterial activity. In particular, the aqueous extracts of BM and GB, the methanolic extract of HI, and the isopropanolic extracts of HI and OS were effective against multiple bacterial strains, including strains with reduced susceptibility to the reference antibiotics bacitracin, oxolinic acid, and streptomycin. These findings highlight the potential of HI, GB and especially OS as functional ingredients or feed additives for aquaculture.