INSECT ALLELOCHEMICALS FROM AJUGA PLANTS

Clerodane diterpenoids and phytoecdysteroids with potential insect antifeedant and moulting hormone activities, respectively, have been isolated from Ajuga plants. Some clerodanes were active against larvae of Egyptian cotton leafworm, Spodoptera littoralis, when present in the diet at 3 ppm doses. Structure-antifeedant activity relations were established. Likewise, first stage larvae of the greenhouse whitefly, Trialeurodes vaporariorum, exhibited complete mortality when fed on A. reptans. This effect was mainly originated by 29-norsengosterone and ajugalactone, two phytoecdysteroids occurring in this plant. For biotechnological production of phytoecdysteroids its total content in different parts of normally grown or in vitro micropropagated A. reptans plants was studied. Great quantitative and qualitative differences were observed. For comparison of these qualitative differences, a dealkylation ratio (Dr = C28/C29 phytoecdysteroid content) and a C-5 hydroxylation ratio (5Hr = 5-OH/5-H phytoecdysteroid content) were established. The 5Hr values appeared to be quite constant ranging from 0.2 to 0.4, whereas Dr values oscillated from 2.3 in whole plants to 12 in root cultures. Production of phytoecdysteroids was highest (congruent-to 5000 ppm/dry wt) in cultures of roots in an hormone supplemented solid medium.