Insect growth regulatory effects by diterpenes from Calceolaria talcana Grau & Ehrhart (Calceolariaceae: Scrophulariaceae) against Spodoptera frugiperda and Drosophila melanogaster ☆

Abstract The n -hexane extract from aerial parts of Calceolaria talcana (Calceolariaceae, formerly Scrophulariaceae) afforded 1,10-α-cyclopropyl-4,13-dimethyl-19-α-hydroxy-9-epi-ent-7,15-isopimaradiene (1,10-cyclopropyl-9-epi-ent-isopimarol) 1 , and 19α-hydroxy-8,11,13-abietatriene 2 together with other known triterpenes and naphthoquinones. These natural products together with n -hexane extract and several fractions showed insecticidal and insect growth regulatory activity against fall armyworm ( Spodoptera frugiperda , Lepidoptera: Noctuidae), and fruit fly ( Drosophila melanogaster , Diptera: Drosophilidae), insect pests of corn and fruits, respectively. The most active samples were a mixture ( M1 ) of the diterpenes 1  +  2 (6:4) that showed insecticidal activity between 10 and 20 ppm. Additionally, a mixture of triterpenes 3 – 5 ( M2 ), fraction 5 ( F-5 ), a mixture of two naphthoquinones 6 , 7 ( M3 ), and the n -hexane extract, which had significant effects between 20.0 and 35.0 μg/mL in diets. Almost all samples were insecticidal with lethal doses between 35 and 50 μg/mL. Our results indicate that these compounds at low concentrations appear to have selective effects on the pre-emergence metabolism of the insect. The results were fully comparable to known natural insect growth inhibitors such as gedunin, MeOH-Cedrela and MeOH-Yucca extracts, suggesting a possible role as natural insecticidal agents.