The effect of fatty acid chain length on nicotine carboxylate insecticide emulsions has been studied in terms of particle size, interfacial tension, nicotine encapsulation on emulsion droplets, and bioactivity. The particle size of the nicotine emulsion and the interfacial tension at the nicotine carboxylate oil phase (0.03 M)--Tween 80 aqueous phase (0.001 M) were affected in a similar way by the change in the fatty acid chain length, which was correlated by the packing conformation of Tween 80 and nicotine carboxylate molecules as obtained by AM1 theoretical calculations. The amount of encapsulated nicotine inside the nicotine carboxylate emulsion droplets influenced the insecticide bioactivity of nicotine; this relationship was explained in terms of the acid value of the different fatty acids used to prepare the nicotine formulation.

The bioactivity of caffeine aqueous solutions (0.20-2.00 wt %) and caffeine oleate emulsions (20 vol % oil, 2.00 wt % surfactant, 0.04 wt % caffeine, 0.05 wt % oleic acid) was assessed against two biological models: Drosophila melanogaster and Hypothenemus hampei. The caffeine aqueous solutions showed no insecticidal activity, whereas caffeine oleate emulsions had high bioactivity against both D. melanogaster and H. hampei. By preparing the caffeine oleate emulsions with anionic surfactants (i.e., sodium lauryl sulfate, sodium laureate, and sodium oleate), we obtained a lethal time 50 (LT50) of 23 min. In the case of caffeine oleate emulsions prepared with nonionic surfactants (i.e., Tween 20 and Tween 80), a LT50 of approximately 17 min was observed. The high bioactivity of the caffeine oleate emulsion against H. hampei opens the possibility of using this insecticide formulation as an effective way to control this pest that greatly affects coffee plantations around the world.

Paracoccidioides brasiliensis is the etiologic agent of one of the most common systemic mycoses in Latin America. As a dimorphic fungus, it must adapt to different environments during its life cycle, either in nature or within the host, enduring external stresses such as temperature or host-induced oxidative stress. In this study we addressed the role of alternative oxidase (PbAOX) in cellular homeostasis during batch culture growth and the morphological transition of P. brasiliensis. Using a PbAOX-antisense-RNA (PbAOX-aRNA) strain with a 70% reduction in gene expression, we show that PbAOX is crucial for maintaining cell viability and vitality during batch culture growth of yeast cells, in what appears to be a pH-dependent manner. We also show that silencing of PbAOX drastically reduced expression levels of other detoxifying enzymes (PbY20 and PbMSOD). In addition, our data indicate that PbAOX plays a role during the morphological transition, namely, during the yeast-to-mycelia germination and mycelia/conidia-to-yeast transition, essential events during the establishment of infection by dimorphic fungal pathogens. Altogether, our findings support the hypothesis that PbAOX is important for the maintenance of cellular homeostasis, possibly by assisting redox balancing during cell growth and the morphological switch of P. brasiliensis.

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ResumenSe realizó un estudio sobre el potencial insecticida agudo y crónico sobre Drosophila melanogaster y antifúngico en Fusarium oxysporum de emulsiones aceite-en-agua de mezclas binarias y ternarias de extractos de Nicotiana tabacum, Azadiractha indica (neem), y aceite esencial de Eucalyptus tereticornis. Se construyeron curvas dosis/respuesta para el tiempo letal medio, relación pupa-huevo, adulto-pupa y porcentaje inhibitorio para la actividad antifúngica. Se observó alta actividad insecticida aguda del tabaco a 6 g/L (tiempo letal medio=2,3 ± 0,5 minutos), larvicida en el neem a 0,2 g/L (pupa-huevo= 0,05) y fungicida en el eucalipto a 3 g/L (porcentaje inhibitorio =100%). Las bioactividades se potenciaron en la mayoría de las mezclas binarias, exceptuando la actividad fungicida. La mezcla ternaria presentó actividad fungicida antagónica. Se concluye sobre la potencial aplicación de estos desarrollos para controlar plagas y enfermedades.Palabras clave: actividad fungicida, actividad insecticida. emulsiones agua-en-aceite, acción conjunta, sinergismo Abstract A study on the acute and chronic insecticide potential on Drosophila melanogaster and antifungal on Fusarium oxysporum of oil-in-water emulsions of binary and ternary mixtures of extracts of Nicotiana tabacum and Azadiractha indica (neem) and Eucalyptus tereticornis essential oil. Dose/response curves for the mean lethal time, pupae-egg ratio, adult-pupae and inhibitory rate for antifungal activity were constructed, compared with the bioactivity mixtures, measuring synergism, antagonism and joint activity. High insecticidal acute activity was observed in tobacco to 6 g/L (mean lethal time=2.3 ± 0.5 minutes), the neem larvicide to 0.2 g/L (pupae-egg ratio=0.05) and fungicide in the eucalyptus to 3 g/L (inhibitory rate=100%). The bioactivities were enhanced in almost all binary and ternary mixtures, except for the fungicidal activity. The ternary mixture exhibits fungicidal activity antagonistic. The study shows the potential application of these technologies to control pests and diseases.