Insecticidal and antifungal activities of Melaleuca rhaphiophylla essential oil against insects and seed-borne pathogens in stored products

Abstract

Essential oils (EOs) are substances with biological properties that can be used to inhibit insects and fungi in storage systems. The EOs from plants of the genus Melaleuca (Myrtaceae) show insecticidal and antifungal activities. However, so far, there are no reports regarding Melaleuca rhaphiophylla (Myrtaceae) EO. Therefore, we sought to investigate the insecticidal and antifungal activities of M. rhaphiophylla EO against storage pests and fungi. The plant’s EO was extracted in a vat using the steam drag method and analyzed by gas chromatography–mass spectrometry. The insecticidal effect against Sitophilus zeamais and Sitophilus oryzae (Coleoptera: Curculionidae) was evaluated through contact and fumigation methods in order to select the optimized exposure route. Then, the lethal concentration (LC), lethal time (LT), and mean survival time (MST) were estimated. Antifungal activity against Aspergillus flavus, Aspergillus niger, Aspergillus nomius and Fusarium graminearum was tested through volatilization and direct contact. Twenty-two compounds were identified in the chemical composition of M. rhaphiophylla EO and the major compounds were α-terpinene (6.46%), 1,8-cineole (11.54%), γ-terpinene (13.2%), terpinolene (28.72%) and terpinen-4-ol (19.82%). The fumigation method of application caused the highest mortality in both insects. The values for LC50 (90.55 and 72.88 of substance L-1 of air), LT50 (0.92 and 1.23 h) and MST (92.17 and 92.67 h) were similar between species (S. zeamais and S. oryzae, respectively). The volatilization method showed low fungicidal activity (< 30% of inhibition) against all isolates. The contact method showed an inhibition greater than 90%with higher toxicity for Aspergillus. Our results showed that M. rhaphiophylla EO has potential as an alternative product to control storage pests and fungi.