Antifeedant activity and effects of terpenoids on detoxication enzymes of the beet armyworm, Spodoptera exigua (Hübner)

Abstract

It has been determined the antifeedant activity of a mixture of limonoids 1,7-di-O-acetylhavanensin and 3,7-di-Oacetylhavanensin (F18), isolated from seeds of Trichilia havanensis Jacq. (Meliaceae), and the neo-clerodane diterpene scutecyprol A, isolated from Scutellaria valdiviana (Clos) Epling (Labiatae), on fifth instar larvae of the beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Choice and no-choice feeding assays, nutritional tests, and post-treatment studies indicated that scutecyprol A acts as an insect feeding deterrent against S. exigua, whereas the antifeedant activity of F18 is likely associated with a toxic mode of action. In addition, it was tested the hypothesis that S. exigua larvae will try to metabolize the compounds that are toxic by the induction of their detoxication systems, whereas no such induction happens for those compounds that are deterrents. The mixture of limonoids F18 significantly increased glutathione S-transferases during the treatment and post-treatment periods, whereas esterases were inhibited during the treatment period. On the contrary, scutecyprol A did not have any significant effect on any of the enzymatic processes. Hence, the metabolic response of S. exigua larvae to the ingestion of the secondary metabolites tested depends on their mode of action.Additional key words: esterases, glutathione S-transferases, limonoids, neo-clerodane diterpenes, nutritional indexes, Scutellaria, Trichilia. ResumenActividad antialimentaria de terpenoides y efectos sobre las enzimas de destoxificación de la gardama, Spodoptera exigua (Hübner) Se ha determinado la actividad antialimentaria de una mezcla de limonoides 1,7-di-O-acetilhavanensina y 3,7-di-O-acetilhavanensina (F18), aislados a partir de semillas de Trichilia havanensis Jacq. (Meliaceae), y del diterpeno neo-clerodano scutecyprol A, procedente de Scutellaria valdiviana (Clos) Epling (Labiatae), frente a larvas de 5º estadío de la gardama, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae). Los resultados de ensayos de preferencia y no preferencia, de ensayos nutricionales y del estudio de los efectos post-ingestivos indican que el scutecyprol A actúa como disuasorio de la alimentación frente a larvas de S. exigua, mientras que la actividad antialimentaria de F18 está asociada a un modo de acción tóxico. Además, se ha comprobado la hipótesis de que las larvas de S. exigua tratan de metabolizar los compuestos que son tóxicos mediante la inducción de enzimas de destoxificación, mientras que esta inducción no es necesaria para aquellos compuestos que son disuasorios de la alimentación. La mezcla de limonoides F18 incrementó de forma significativa la actividad glutatión S-transferasa durante los periodos de tratamiento y post-tratamiento, mientras que la actividad esterasa se redujo durante el periodo de tratamiento. Por el contrario, el scutecyprol A no tuvo ningún efecto significativo sobre estos procesos enzimáticos. Se puede concluir, pues, que la respuesta metabólica en larvas de S. exigua depende del...

Synthesis of thymyl esters and their insecticidal activity against Spodoptera litura (Lepidoptera: Noctuidae)

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Bioactivity of a water extract of boldus (Peumus boldus Molina) against Spodoptera frugiperda (J.E. Smith) and Helicoverpa zea Boddie (Lepidoptera: Noctuidae)

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Chemicals isolated from Justicia adhatoda Linn reduce fitness of the mosquito, Aedes aegypti L

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