Identification and quantification of phytoecdysteroids and clerodanes content in three wild Ajuga species in Israel: Potential activity against pests

Ajuga plants (family Lamiaceae) contain phytoecdysteroids and clerodanes. Phytoecdysteroids are triterpene-derived analogues of steroid hormones that control molting and metamorphosis in arthropods, whereas clerodanes diterpenes deter phytophagous insects. In this study, we identified and quantified phytoecdysteroid and clerodane contents in three Ajuga species in Israel. Our objectives were to use these metabolites as environmentally and friendly control methods against insects. Leaves and roots of A. iva, A. chamaepitys (A. chia) and A. orientalis were collected from Israel. Using liquid chromatography–time of flight–mass spectrometry analysis (LC-TOF-MS), we identified three phytoecdysteroids: 20-hydroxyecdysone (ecdysterone), makisterone-A and cyasterone, and two clerodanes: dihydroajugapitin and columbin. Phytoecdysteroid contents varied significantly among species and organs. The highest concentrations of three phytoecdysteroids were recorded in A. iva. Cyasterone content tended to be higher in leaves of A. chamaepitys. Dihydroajugapitin concentration was highest in A. iva leaves but was lower or undetectable in the roots, and in the other two species. Columbin concentration was similar in all species and organs. To test the biological activity of Ajuga extracts against Spodoptera littoralis, leaves of Castor bean were smeared with water - crude extract including phytoecdysteroid and clerodanes. For each repeat, 10 1^st and 3^st instar of S. littoralis larvae were fed with one treated leaf for 3 and 4 days respectively. Larval weight gain (LWG) and survival was compared to control (leaves smeared with water). Crude extract from A. iva leaves (50, 100 and 500µg/µl), significantly increased mortality of S. littoralis 1^st instar larvae (36%, 70% and 87% respectively) compared to the control (6%). Additionally, S. littoralis LWG of 3^rd was significantly decreased by (65%, 69% and 44% respectively) as compared with the relevant controls.

Since phytoecdysteroids have disruptive effects on phytophagous insect growth, the potential role of extracts of A. iva in pest-management programs are of interest.