Caterpillars Detoxify Diterpenoid from Nepeta stewartiana by the Molting Hormone Gene CYP306A1.

Herbivorous insects are well known for detoxifying a broad range of the defense compounds produced by the plants that they feed on, but knowledge of the mechanisms of detoxification is still very limited. Here, we describe a system in which two species of lepidopteran caterpillars metabolize an abietane diterpene from the plants of Nepeta stewartiana Diels to an oxygenated derivative that is less active biologically. We found that this transformation could be catalyzed by a cytochrome P450 enzyme in caterpillars, which are associated with molting. Most interestingly, abietane diterpene targets the molting-associated gene CYP306A1 to alter the content of molting hormones in the insect at specific developmental stages and competitively inhibit molting hormone metabolism. These findings identify the mechanism by which caterpillars are able to detoxify abietane diterpenoid through hydroxylation at the C-19 position, which may be opening up exciting research questions into the mechanisms of interaction between plants and insects.

Insecticidal Terpenes From the Essential Oils of Artemisia nakaii and Their Inhibitory Effects on Acetylcholinesterase.

Essential oils (EOs) are often the source of insecticidal substances of high efficiency and low toxicity. From gas chromatograph-mass spectrometer, column chromatography, and nuclear magnetic resonance spectra analyses, twenty terpenes were identified from the EOs of Artemisia nakaii. These comprised mostly monoterpenes (49.01%) and sesquiterpenes (50.76%). The terpenes at the highest concentrations in the EOs of A. nakaii were feropodin (200.46 ± 1.42 µg/ml), (+)-camphor (154.93 ± 9.72 µg/ml), ß-selinene (57.73 ± 2.48 µg/ml), and 1,8-cineole (17.99 ± 1.06 µg/ml), calculated using area normalization and external standards. The EOs were tested for biological activity and showed strong fumigant toxicity and significant antifeedant activity against the larvae of Spodoptera litura. Furthermore, the monoterpenes 1,8-cineole and (+)-camphor displayed significant fumigant activity against S. litura, with LC50 values of 7.00 ± 0.85 and 18.16 ± 2.31 µl/L, respectively. Antifeedant activity of the sesquiterpenes feropodin and ß-selinene was obvious, with EC50 values of 12.23 ± 2.60 and 10.46 ± 0.27 µg/cm2, respectively. The EOs and ß-selinene were also found to inhibit acetylcholinesterase, with IC50 values of 37.75 ± 3.59 and 6.88 ± 0.48 µg/ml, respectively. These results suggest that monoterpenes and sesquiterpenes from the EOs of A. nakaii could potentially be applied as a botanical pesticides in the control of S. litura.