Development, characterization, insecticidal and sublethal effects of Bunium persicum and Ziziphora clinopodioides-based essential oil nanoemulsions on Culex quinquefasciatus

Abstract

Essential oils (EOs) represent innovative and safe botanical pesticides to be exploited in different fields, including agriculture, being often obtained by cheap and easily available plant crops. However, their use is threatened by some limits, which are mainly linked to their physico-chemical properties. In this regard, the use of nanoemulsions (NEs) usually enables to overcome these limits but often also to improve the biological activities of these products. Bunium persicum (Boiss.) B Fedtsch. and Ziziphora clinopodioides Lam. are two aromatic plants of economic interest well known for their traditional food and medical uses. Their EOs exhibited several biological properties, including a remarkable insecticidal activity against different targets. Here, the chemical analysis of the two EOs revealed the predominance of γ-terpinene (35.8%), cumin aldehyde (16.6%), γ-terpinen-7-al (14.0%), and α-terpinen-7-al (11.7%) for B. persicum, and pulegone (55.6%), piperitenone (12.8%), and iso-menthone (8.0%) for Z. clinopodioides. NEs were successfully obtained by high-pressure homogenization or ultrasonication method, using polysorbate 80 as emulsifier. The EOs and their 10% NEs were evaluated against larvae and pupae of Culex quinquefasciatus Say mosquitoes. In detail, both EOs exhibited a good larvicidal efficacy (LC50 of 35.8 and 68.9 µL L−1 for B. persicum and Z. clinopodioides, respectively). Bunium persicum EO NE showed higher efficacy than the EO alone (LC50 = 290.4 µL L−1), considering that only the 10% of the EO was encapsulated. Conversely, Z. clinopodioides NE showed the same efficacy than the EO alone (LC50 of 759.8 µL L−1). In addition, both NEs displayed significantly better sublethal toxicity compared with the EOs. Moreover, even if no significant mortality was detected in the pupal stage, only 12% of the larvae pupated and emerged as adults in the case of the NE from B. persicum. In conclusion, both EOs and their NEs could be promising candidates for the development of botanical pesticides, also considering the commercial availability and affordability of these EOs.