Fumigant toxicity and biochemical effects of selected essential oils toward the red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae).

Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is an insect popularly known as the red flour beetle, it is widely distributed worldwide and can cause serious damage to stored grains. Chemical control is the most used method for managing this pest, however, some substances are toxic to mammals and the environment. Therefore, the development of new effective and safe insecticides is necessary. Essential oils (EOs) can be considered as a potential alternative in the development of pesticides due to their physicochemical properties and varied effects against insects. In the current study, was determined the fumigant toxicity and biochemical effects of selected essential oils against T. castaneum. The 23 selected EOs were characterized by GC-MS and their fumigant lethal concentrations were determined. An exploratory Cluster analysis was performed to find a relationship between fumigant toxicity and chemical composition. Finally, the inhibition of the catalytic activity of acetylcholinesterase (AChE), glutathione S-transferase (GST) and catalase (CAT) was evaluated using protein homogenates obtained from T. castaneum. The results indicated that EOs with the highest fumigant potential were those with greater diversity in their composition, while the least active EOs presented mainly monoterpenes. The most active EOs were those obtained from Foeniculum vulgare and Zanthoxylum monophyllum with LC50 values of 16.23 and 18.54 µL/L air respectively. Regarding the inhibition of the enzymatic activity of the 23 EOs evaluated at 500 µL/L, only two caused an inhibition greater that 50% on AChE, which corresponded to EOs from Piper nigrum and Rosmarinus officinalis. Likewise, EOs from C. sinensis, Piper aduncum and Zanthoxylum monophyllum were the only ones able to inhibiting GST activity by more than 50%. Respecting CAT inhibition, 7 EOs caused and inhibition greater than 50%, highlighting those from Lavandula angustifolia, C. sempervirens and Eucalyptus sp. These results show that the EOs evaluated in this study seems to be a promising bio-controller of T. castaneum since have high fumigant toxicity and exert different mechanisms of action.

Effects of Essential Oils from 24 Plant Species on Sitophilus zeamais Motsch (Coleoptera, Curculionidae).

Chemical control of the maize weevil (Sitophilus zeamais) has been ineffective and presents serious collateral damage. Among plant-derived insecticides, essential oils (EOs) are suitable candidates to control this stored products pest. In this work, the insecticidal activities of 45 natural EOs against S. zeamais adults were screened, and the most promising ones (24 EOs) were characterized by GC-MS. The repellent and toxic effects (contact and fumigant) of these 24 EOs were determined, and by a cluster analysis they were classified into two groups considering its fumigant activity and contact toxicity. For the EOs with the highest fumigant potential (14 oils) and their main active constituents (17 compounds), lethal concentrations were determined. The most active EOs were those obtained from L. stoechas and L. alba, with LC50 values of 303.4 and 254.1 µL/L air and characterized by a high content of monoterpenes. Regarding the major compounds, the oxygenated monoterpenes R-(+)-pulegone (LC50 = 0.580 mg/L air), S-(-)-pulegone (LC50 = 0.971 mg/L air) and R-(-)-carvone (LC50 = 1.423 mg/L air) were the most active, as few variations in their concentrations significantly increased insect mortality.