Allelochemical effects were observed when Tribolium castaneum (Herbst) adults were treated with Baccharis salicifolia (Ruiz & Pavon) Pers essential oil. The main biological activities were toxicity and repellence. Terpenes present in the essential oil were identified by GC-MS, and some authentic samples were tested to assess their activity individually. The most acutely toxic compounds after 3 days were beta-pinene and pulegone. Most of the monoterpenes elicited symptoms indicative of neurotoxicity. The most repellent compound was alpha-terpineol. Toxic and repellent effects of chemical derivatives of the major sesquiterpene present in B salicifolia essential oil, as well as a series of monoterpenes, were evaluated in order to investigate structure-activity relationships. The reduced derivatives of the monoterpenes and sesquiterpenes were more repellent that their carbonyl analogues. In addition, unsaturation in the germacrane skeleton enhanced repellent activity.
Fourteen clerodane-type diterpenoids isolated from plants in the genera Baccharis, Teucrium, and Salvia were assayed for antifeedant activity against Tenebrio molitor larvae in order to establish structure-activity relationships. Among the compounds tested, furanoditerpenes with alpha, beta-unsaturated-gamma-lactone moieties, or C-4-epoxy substitution with C-5-methylacetoxy or C-12-acyloxy functionalities, exhibited maximal antifeedant and repellent activities.
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