RESUMEN
Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-free space. Female leafminers preferred laying their eggs on Vicia faba (Fabaceae) over Beta vulgaris var. cicla (Chenopodiaceae), in both laboratory and field choice experiments, although no oviposition preference was observed in no-choice tests. Females fed more often on B. v. var. cicla (no-choice test) or showed no feeding preference (choice test), even when their realized fecundity was remarkably higher on V. faba. Offspring developed faster, tended to survive better, and attained bigger adult size on the preferred host plant. Also, a field experiment showed higher overall parasitism rates for leafminers developing on B. v. var. cicla, with a nonsignificant similar tendency in field surveys. According to these results, host plant selection by L. huidobrensis appears to be driven mainly by variation in host quality. Moreover, the consistent oviposition choices for the best host and the labile feeding preferences observed here, suggest that host plant selection might be driven by maximization of offspring fitness even without a conflict of interest between parents and offspring. Overall, these results highlight the complexity of decisions performed by phytophagous insects regarding their host plants, and the importance of simultaneous evaluation of the various driving forces involved, in order to unravel the adaptive significance of female choices.
Asunto(s)
Dípteros/fisiología , Preferencias Alimentarias , Interacciones Huésped-Parásitos , Oviposición , Animales , Beta vulgaris/parasitología , Dípteros/parasitología , Femenino , Larva/crecimiento & desarrollo , Masculino , Pupa/crecimiento & desarrollo , Vicia faba/parasitologíaRESUMEN
We examined the effects of the flavonoids pinocembrin and quercetin on the feeding behavior, survival, and development of the Cucurbitaceae pest Epilachna paenulata (Coleoptera: Coccinellidae). In no-choice experiments, 48 hr-consumption of Cucurbita maxima Duch. leaves treated with pinocembrin at 1, 5, and 50 microg/cm(2) was less than one third of that for leaves treated with 0.1 microg/cm(2) of pinocembrin or untreated leaves. Larvae stopped feeding after 9 days of high doses of pinocembrin (5 and 50 microg/cm(2)), and larval weight and survival were negatively affected by pinocembrin at 1-50 microg/cm(2). Delayed mortality in comparison to food-deprived larvae suggests that the mechanism of action for pinocembrin is chronic intoxication, rather than simple starvation from antifeedant effects. In contrast, leaf consumption and larval weight were not significantly affected by quercetin (at 0.1, 1, 5, and 50 microg/cm(2)) while mortality rates were only slightly increased. The response of E. paenulata larvae in a choice-test to combinations of pinocembrin at antifeedant doses (5 and 50 microg/cm(2)) and quercetin at phagostimulant doses (0.01 and 0.1 microg/cm(2)) indicated that the feeding deterrent activity of the former completely overshadowed the stimulant activity of the latter. These results demonstrate the different responses of one insect species to two widely distributed plant flavonoids. Pinocembrin strongly affected survival of E. paenulata while quercetin had only a weak effect without major consequences on the insect life-cycle.
Asunto(s)
Escarabajos/efectos de los fármacos , Flavanonas/farmacología , Quercetina/farmacología , Animales , Peso Corporal/efectos de los fármacos , Escarabajos/crecimiento & desarrollo , Escarabajos/fisiología , Relación Dosis-Respuesta a Droga , Conducta Alimentaria/efectos de los fármacos , Flavanonas/toxicidad , Larva/efectos de los fármacos , Larva/crecimiento & desarrollo , Larva/fisiología , Dosificación Letal Mediana , Análisis de SupervivenciaRESUMEN
Aerial parts of 27 plant species native to Argentina were tested in anti-insect, germination inhibition and bactericide bio-assays. In antifeedant assays on Epilachna paenulata larvae, 11 species showed strong feeding deterrent effects (higher than 90% at 200 microg/cm(2)). Twelve plants strongly inhibited the germination of Avena sativa seeds, but only six inhibited Raphanus sativum germination at 10 mg/ml. Four plants showed complete growth inhibition of Escherichia coli at a concentration of 2 mg/ml.
Asunto(s)
Antibacterianos/farmacología , Escherichia coli/efectos de los fármacos , Plaguicidas/farmacología , Fitoterapia , Extractos Vegetales/farmacología , Plantas Medicinales , Animales , Antibacterianos/administración & dosificación , Antibacterianos/uso terapéutico , Avena/crecimiento & desarrollo , Escarabajos/efectos de los fármacos , Escarabajos/fisiología , Conducta Alimentaria , Germinación/efectos de los fármacos , Interacciones Huésped-Parásitos , Larva/efectos de los fármacos , Pruebas de Sensibilidad Microbiana , Componentes Aéreos de las Plantas , Extractos Vegetales/administración & dosificación , Extractos Vegetales/uso terapéutico , SemillasRESUMEN
Ethanolic extract of aerial parts of Artemisia annua L. and artemisinin were evaluated as anti-insect products. In a feeding deterrence assay on Epilachna paenulata Germ (Coleoptera: Coccinellidae) larvae, complete feeding rejection was observed at an extract concentration of 1.5 mg/cm2 on pumpkin leaf tissue. The same concentration produced a feeding inhibition of 87% in Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae). In a no-choice assay, both species ate less and gained less weight when fed on leaves treated with the extract. Complete mortality in E. paenulata and 50% mortality in S. eridania were observed with extract at 1.5 mg/cm2. Artemisinin exhibited a moderate antifeedant effect on E. paenulata and S. eridania at 0.03-0.375 mg/cm2. However, a strong effect on survival and body weight was observed when E. paenulata larvae were forced to feed on leaves treated at 0.03 and 0.075 mg/cm2. Artemisia annua ethanolic extract of aerial parts at 1.5 mg/cm2 showed no phytotoxic effect on pumpkin seedlings.
Asunto(s)
Artemisia/metabolismo , Artemisia/parasitología , Escarabajos/fisiología , Conducta Alimentaria , Interacciones Huésped-Parásitos , Extractos Vegetales/metabolismo , Animales , Larva/fisiología , Hojas de la PlantaRESUMEN
Plant tissues may show chemical changes following damage. This possibility was analyzed for Minthostachys mollis, a Lamiaceae native to Central Argentina with medicinal and aromatic uses in the region. Effects of mechanical damage on its two dominant monoterpenes, pulegone and menthone, were analyzed by perforating M. mollis leaves and then assessing essential oil composition at 24, 48, and 120 hr; emission of volatiles was also measured 24 and 48 hr after wounding. Mechanical damage resulted in an increase of pulegone and menthone concentration in M. mollis essential oil during the first 24 hr. These changes did not occur in the adjacent undamaged leaves, suggesting a lack of systemic response. Postwounding changes in the volatiles released from M. mollis damaged leaves were also detected, most noticeably showing an increase in the emission of pulegone. Inducible chemical changes in aromatic plants might be common and widespread, affecting the specific compounds on which commercial exploitation is based.
Asunto(s)
Insectos/fisiología , Lamiaceae/química , Aceites Volátiles/análisis , Hojas de la Planta/química , Aceites de Plantas/análisis , Animales , Argentina , Monoterpenos Ciclohexánicos , Lamiaceae/metabolismo , Mentol/análisis , Monoterpenos/análisis , Aceites Volátiles/química , Hojas de la Planta/metabolismo , Aceites de Plantas/químicaRESUMEN
Plants display a diverse array of inducible changes in secondary metabolites following insect herbivory. Herbivores differ in their feeding behavior, physiology, and mode of attachment to the leaf surface, and such variations might be reflected in the induced responses of damaged plants. Induced changes were analyzed for Minthostachys mollis, a Lamiaceae with medicinal and aromatic uses, and four species of folivore insects with different feeding habits (chewing, scraping, sap-sucking, and puncturing). In M. mollis leaves experimentally exposed to the insects, levels of the two dominant monoterpenes pulegone and menthone were assessed 24 and 48 h after wounding. Menthone content generally decreased in the essential oil of damaged leaves, whereas pulegone concentration increased in all treatments. These changes occurred also in the adjacent undamaged leaves, suggesting a systemic response. The relatively uniform response to different kinds of damage could be attributable to the presence of such a strongly active compound as pulegone in the essential oil of M. mollis. The effects of wounding on essential oil concentration may be significant from a commercial point of view.
Asunto(s)
Insectos/fisiología , Lamiaceae/metabolismo , Aceites Volátiles/química , Hojas de la Planta/metabolismo , Animales , Monoterpenos Ciclohexánicos , Conducta Alimentaria , Lamiaceae/química , Mentol/análisis , Monoterpenos/análisis , Hojas de la Planta/químicaRESUMEN
Plant tissues may show chemical changes following herbivory. In aromatic plants such changes could affect the specific compounds on which commercial exploitation is based. This possibility was analyzed for Mintosthachys mollis, a member of the Lamiaceae native to Central Argentina with medicinal and aromatic uses in the region, and two types of insect herbivores: a leaf miner and a gall insect. Analysis of the essential oils of mined/undamaged leaves, as well as leaves from stems with and without galls, revealed changes in concentrations of the two main monoterpenes. A decrease in pulegone concentration was associated with both types of insect damage, whereas menthone increased significantly only in mined leaves. Inducible chemical changes in aromatic and medicinal plants may be common and widespread; their economic implications deserve investigation.