Toxicity and Synergistic Effect of Elsholtzia ciliata Essential Oil and Its Main Components against the Adult and Larval Stages of Tribolium castaneum

Investigations have indicated that storage pests pose a great threat to global food security by damaging food crops and other food products derived from plants. Essential oils are proven to have significant effects on a large number of stored grain insects. This study evaluated the contact toxicity and fumigant activity of the essential oil extract from the aerial parts ofElsholtzia ciliataand its two major biochemical components against adults and larvae of the food storage pest beetleTribolium castaneum. Gas chromatography–mass spectrometry analysis revealed 16 different components derived from the essential oil ofE. ciliata, which included carvone (31.63%), limonene (22.05%), andα-caryophyllene (15.47%). Contact toxicity assay showed that the essential oil extract exhibited a microgram-level of killing activity againstT. castaneumadults (lethal dose 50 (LD50) = 7.79 μg/adult) and larvae (LD50= 24.87 μg/larva). Fumigant toxicity assay showed LD50of 11.61 mg/L air for adults and 8.73 mg/L air for larvae. Carvone and limonene also exhibited various levels of bioactivity. A binary mixture (2:6) of carvone and limonene displayed obvious contact toxicity againstT. castaneumadults (LD50= 10.84 μg/adult) and larvae (LD50= 30.62 μg/larva). Furthermore, carvone and limonene exhibited synergistic fumigant activity againstT. castaneumlarvae at a 1:7 ratio. Altogether, our results suggest thatE. ciliataessential oil and its two monomers have a potential application value to eliminateT. castaneum.Keywords:Elsholtzia ciliata;Tribolium castaneum;essential oil;carvone;limonene;insecticidal activity;synergistic effect