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 20ppm. 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 35.0μg/mL in diets. Almost all samples were insecticidal with lethal doses between 35 and 50μg/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.