Cocktail effect and synergistic mechanism of two components of Perilla frutescens essential oil, perillaldehyde and carvone, against Tribolium castaneum

Abstract

Tribolium castaneum (Herbst) is one of the most harmful insects in stored products. The objective of the current study was to search for active constituents of Perilla frutescens (L.) Britt. essential oils from three localities against T. castaneum, as well as to investigate the optimal formula of active constituents and their synergistic mechanism. A total of 38 constituents were identified from the three essential oils by gas chromatography-mass spectrometry (GC-MS) according to the mass spectra and retention index values, and the relative contents of the individual components were determined by the peak normalization method. The following major compounds were identified: perillaldehyde, (R)-(-)-carvone, 2-furyl methyl ketone, d-limonene, and β-caryophyllene. Contact toxicity was assessed by topical application under room temperature, and the insects were reared in a dark incubator for 24 h at approximately 30 °C and 75 % humidity. Of these compounds, perillaldehyde (LD50 =7.71 μg/adult) and R-(-)-carvone (LD50 =10.93 μg/adult) displayed the most significant contact activities against T. castaneum. Synergistic interactions between perillaldehyde and R-(-)-carvone were evaluated using Wadley's model. All nine tested formulas displayed synergistic effects against T. castaneum, and a 1:4 (v:v) mixture exhibited an intense cocktail effect by dramatically reducing the LD50 to 2.73 μg/adult. The results of the RNA-Seq and qRT-PCR analyses suggested that the synergistic effect could be attributed to a reduced capacity for detoxification and elimination of xenobiotics. Three cytochrome P450 genes (CYP6BQ11, CYP6BQ7, and CYP6BK5) in phase I and two multidrug resistance protein genes (MRP4a and MRPX4) in phase III of the detoxification process may play essential roles. These findings provide a basis for the development of novel natural insecticides for the control of storage pests.