Insecticidal activity of forty-seven marine algae species from the Mediterranean, Aegean, and Sea of Marmara in connection with their cholinesterase and tyrosinase inhibitory activity

• Insecticidal activity of 47 macroalgae mostly from Mediterranean Sea was examined. • Cholinesterase and tyrosinase inhibitory effect of the alga extracts was investigated. • D. dichotoma var. intricata was the only one exhibiting BChE inhibition over 50%. • BChE inhibition by four diterpenes in DDI was investigated in silico . • The macroalgae and their metabolites might be new sources of novel insecticides. Ethanolic extracts prepared from forty-seven macroalgae species collected from the Mediterranean Sea, Aegean Sea, and Sea of Marmara were tested at 200 μg/mL against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and tyrosinase (TYR), crucial for insect vivacity. Only one alga extract, e.g . Dictyota dichotoma var. intricata (C.Agardh) Greville 1830, had a notable inhibition of BChE (72.0 ± 0.07%), whereas the rest of the macroalgae possessed no or low inhibition of AChE (2.20 ± 0.39% - 14.20 ± 2.16%), BChE (0.62 ± 0.07% - 41.20 ± 3.07%), and TYR (< 10%). Several known diterpenes (isoamijiol, 14-deoxyamijiol, amijidictyol, dictyodial, and 4α-acetoxydictyodial) found earlier in this species were proceeded to molecular docking experiments to figure out its interactions with BChE. Eleven of the 47 macroalgal extracts were selected based on sufficient availability for testing in larvicidal and adulticidal activity assays against female Aedes aegypti “Orlando1952” the mosquito vector of yellow fever and dengue. The selected extracts displayed a high adulticidal activity ranging between 80–100% activity at 5 μg/mosquito. In contrast, only the ethanol extract of Ceramium siliquosum var. elegans showed larvicidal mortality of 93.3 ± 11.5% at 0.5 μg/mL. Our findings show that the macroalgae and their metabolites could be sources of novel insecticidal agents.