Effect of Azadirachta indica A. Juss (Meliaceae) on the serotonin rhythm of Spodoptera frugiperda (Lepidoptera: Noctuidae).

Circadian rhythms are an adaptive response of organisms to the environment that enables them to measure time. Circadian rhythms are some of the most studied biological rhythms. Serotonin (5HT) has been proposed as their modulator of circadian rhythms, playing a pivotal role in their establishment. However, 5HT concentrations are altered in insect organisms when they feed on some plant extracts. Insects show a variety of rhythms. The larval stage of the lepidopteran Spodoptera frugiperda is a pest of economically important crops. As a response, plants have developed secondary metabolites, such as azadirachtin, obtained from Azadirachta indica. We assessed the circadian rhythm of 5HT in the brain and digestive tube of larvae of S. frugiperda; furthermore, the effect of A. indica extract on the oscillations was evaluated. 5HT modulates the rhythms of locomotor activity, and if extracts of A. indica alter the concentration of 5HT, it can indirectly alter the rhythms of locomotor activity, as well as peristaltic movements of the intestine. Larvae were exposed to a 12 h:12 h light-dark (LD) photoperiod, and half of them remained for 72 h under constant darkness (DD). Tissue samples were obtained at six different times during a single 24 h period, and the amount of 5HT was quantified by high-performance liquid chromatography (HPLC). Data were statistically compared by a one-way ANOVA followed by a Tukey post hoc test and subjected to Cosinor analysis for assessment of 24 h rhythmicity. The results showed that the A. indica methanolic extract had an effect on the 5HT concentration of the brain and digestive tube of the larvae. In the brain, the 5HT increase in larvae fed with the extract could alter memory, learning, sleep, and locomotor activity processes. Whereas in the intestine, the 5HT decrease in the larvae fed with the extract could decrease peristalsis movements and, therefore, indirectly influence the antifeedant effect.

Biocidal effect of a hexane-soluble extract of Lippia graveolens Kunth (Verbenaceae) / Efecto biocida del extracto hexánico de Lippia graveolens Kunth (Verbenaceae)

Lippia graveolens Kunth (Verbenaceae) is an economically important shrub known in Mexico as Oregano. In this work, the biocidal effect of the hexane extract of L. graveolens leaves was evaluated on two crop pests. Thus, larvae of Spodoptera frugiperda were fed with mixtures of extract and artificial diet. The nematicidal activity was evaluated on juveniles of Meloydogine javanica. Regarding S. frugiperda, quantitative differences between treatments and control were observed in dead pupae, surviving adults, and deformed adults (P < 0.05). All the surviving adults from the extract treatments were deformed. Nematicidal effect was registered, the LC50 and LC90 were 0.672 (0.654-0.690) and 0.965 (0.937-0.998) mg/mL respectively. The extract was characterized by NMR and GC-MS, being thymol the most abundant component (70.6%) in addition to carvacrol (22.8%). The results suggest the consideration of the hexane extract of L. graveolens leaves within the alternatives for the biological control of pests.

Lippia graveolens Kunth (Verbenaceae) es un arbusto con importancia económica conocido en México como Orégano. En éste trabajo se evaluó el efecto biocida del extracto hexánico de hojas L. graveolens sobre dos plagas agrícolas. Así, larvas de S. frugiperda fueron alimentadas con mezclas de dieta artificial y extracto. La actividad nematicida fue evaluada en juveniles de Meloydogine javanica, Respecto a S. frugiperda, se observaron diferencias cuantitativas entre tratamiento y control en cuanto a pupas muertas, adultos sobrevivientes y adultos deformes (P < 0.05). Todos los adultos provenientes de tratamientos con extracto estuvieron malformados. Hubo efecto nematicida, calculándose CL50 y CL90 de 0.672 (0.654-0.690) y 0.965 (0.937-0.998) mg/mL respectivamente. El extracto se caracterizó por RMN y CG-EM. Los compuestos más abundantes fueron timol (70.6%), ademas del carvacrol (22.8%). Los resultados sugieren considerar al extracto hexánico de hojas de L. graveolens dentro de las alternativas para el control biológico de plagas.