Insecticidal and antibacterial effects of some essential oils against the poultry pest Alphitobius diaperinus and its associated microorganisms

Alphitobius diaperinus is a worldwide poultry pest which causes several problems, including the dispersion of pathogenic microorganisms. This study aimed to evaluate the insecticidal activity of five essential oils (EOs) against A. diaperinus and their antimicrobial activity against some pathogenic bacteria transmitted by this insect and against the mesophilic bacteria present on its external surface. The chemical composition of the EOs was determined, with the major components being: α-thujone in Aloysia polystachya EO; limonene in Citrus sinensis EO; 1,8-cineole in Eucalyptus globulus EO; terpinolene and thymol in Origanum vulgare EO; and eugenol in Syzygium aromaticum EO. The EO of A. polystachya showed the highest fumigant activity (LC50 = 27.25 µL/L of air), followed by E. globulus EO (LC50 = 36.49 µL/L of air). The EOs of S. aromaticum, O. vulgare, and A. polystachya revealed high contact toxicity, with LC50 values of 0.052, 0.128, and 0.135 µL/cm2, respectively. In addition, EOs obtained from O. vulgare and S. aromaticum strongly inhibited the growth of Escherichia coli and Staphylococcus aureus and significantly reduced the microbial load of the insect. Syzigium aromaticum and O. vulgare affected both insects and bacteria, making them promising candidates to replace synthetic insecticides or to be incorporated into current strategies for the management of A. diaperinus, and also helping to reduce the bacteria associated with this coleopteran. To our knowledge, this is the first report of the insecticidal activity of the five selected EOs on A. diaperinus adults, as well as the effect of EOs on the microbial load of insects.