Larvicidal activities of Cnidium officinale Makino extract encapsulated with cellulose nanocrystal-stabilized Pickering emulsion against Aedes albopictus Skuse, a vector of Zika virus

Phytochemicals extracted from plant structures are an appropriate alternative pesticide to prevent side effects from synthetic pesticides, such as environmental problems, direct damage to other organisms, and strong mutations. Since some phytochemicals with larvicidal activities against mosquito larvae have low surface tension, phytochemicals must be encapsulated with hydrophilic structures to be applied in the aqueous phase. Here, we suggest a phytochemical encapsulation method with sulfated cellulose nanocrystal (S-CNC) via Pickering emulsification. Before Pickering emulsification, 11 herbal plant extracts were studied for their larvicidal activities against Aedes albopictus Skuse to investigate a novel plant extract found in traditional medicine in Northeast Asian countries. Among them, Cnidium officinale Makino and Syzygium aromaticum (L.) Merr. & L. M. Perry exhibited outstanding larvicidal activity, and C. officinale showed approximately 1.9-fold higher larvicidal activity than S. aromaticum at the same concentration. After analysis of C. officinale root methanol extract (CoRM), we emulsified CoRM with various concentrations of S-CNC to improve the low solubility of CoRM to the aqueous phase. The colloidal stability of S-CNC-stabilized CoRM Pickering emulsion was examined in terms of phase behavior, droplet size distribution, rheological properties, surface tension, and zeta potential during storage. Then, we investigated the larvicidal activity of the Pickering emulsion, and Pickering emulsified CoRM showed 100% mortality at 0.125 mg mL−1 concentration against Ae. albopictus larvae. These results demonstrated that the Pickering emulsification with S-CNC can be utilized to encapsulate the larvicidal plant extracts, leading to improved management of insect-borne diseases.