Carlina acaulis and Trachyspermum ammi essential oils formulated in protein baits are highly toxic and reduce aggressiveness in the medfly, Ceratitis capitata

Abstract

Essential oil (EO)-based botanical insecticides are considered a promising option for Integrated Pest Management (IPM). However, the sublethal effects of EO-based insecticides are understudied. No information is available on the potential effects of EO exposure on insect aggressive traits. In this study, the toxicity of two EOs with documented efficacy on insect vectors and agricultural pests, and which were obtained from the roots of silver thistle (Carlina acaulis L., Asteraceae) and seeds (i.e. schizocarps) of ajwain (Trachyspermum ammi (L.) Sprague, Apiaceae), was evaluated against adults of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (medfly), a cosmopolitan frugivorous pest. Both EOs were formulated in a mucilaginous solution containing sucrose and hydrolyzed proteins, suitable for “attract and kill” tests. After testing the EO ingestion toxicity on medflies, lethal concentrations LC10, and LC30 were calculated. Behavioral tests were carried out to assess the effect of EO feeding on the medfly aggressive traits. Both EOs formulated in protein baits showed promising insecticidal activity on medflies. Lethal concentrations 50 (LC50) of C. acaulis and T. ammi EOs were 1094 ppm and 3963 ppm, respectively. Medflies fed on protein baits treated with EO LC10 and LC30 showed a significant reduction in the overall abundance of aggressive interactions at the population level, as well as shorter aggression duration over control flies. Concerning aggression scores, no differences were found between treated and control flies. This study underlines the promising potential of C. acaulis and T. ammi EOs for the development of eco-friendly formulations to be used in medfly “attract and kill” approaches. It also outlined how exploiting food sources contaminated by low EO concentrations can strongly impact medfly aggressiveness, which is of key importance for the successful reproduction of this important fruit pest.