Mathematical Modeling for Studying the Sustainability of Plants Subject to the Stress of Two Distinct Herbivores

Viability of plants, especially endangered species, are usually affected by multiple stressors, including insects, herbivores, environmental factors and other plant species. We present new mathematical models, based on systems of ordinary differential equations, of two distinct herbivore species feeding (two stressors) on the same plant species. The new feature is the explicit functional form modeling the simultaneous feedback interactions (synergistic or additive or antagonistic) between the three species in the ecosystem. The goal is to investigate whether the coexistence of the plant and both herbivore species is possible (a sustainable system) and under which conditions sustainability is feasible. Our theoretical analysis of the novel model without including competitions among the two herbivores reveals that the number of equilibrium states and their local stability depends on the type of interaction between the stressors: synergistic or additive or antagonistic. Our numerical results, based on value of parameters available, suggest that a sustainable system requires significant herbivore inter- or intra-species competition or both types. Additionally, our numerical findings indicate that competition and interaction of additive type promotes coexistence equilibrium states with the highest plant biomass. Furthermore, the system can exhibit periodic behavior and show the potential for multi-stability

Seasonal Occurrence and Distribution on Grapevine Roots of Eurhizococcus brasiliensis (Wille) (Hemiptera: Margarodidae) in Brazil

The ground pearl, Eurhizococcus brasiliensis (Wille) (Hemiptera: Margarodidae), is the most importantgrapevine pest in Brazil. Its seasonal occurrence and distribution on the roots of the different developmentstages were determined to allow better monitoring of this insect and better targeting of its vulnerable lifestages. Yellow cysts (after the first nymphal moult) showed the lowest density in October, followed by agradual increase towards August. White cysts (cysts with enclosed pre-pupal males or females) occurredfrom August to December, with a peak in November. Mobile females (adult females emerging from thewhite cysts) were found from August to December, with a peak in August. Parthenogenetic females thatremain in the ruptured white cysts for egg laying were present from August to April, with a peak inNovember. Mobile nymphs (first instar) were also found from August to April, with a peak in December.Yellow cysts were most abundant at depths of 0 to 25 cm. The horizontal survey showed that cysts occurredmostly on the trunk below the ground (trunk of the rootstock), and that almost all occurred in an area of20 cm width around the trunk. These results provide important information for better monitoring of thispest and to develop better methods for and timing of chemical control

Morphological and electrophysiological properties of pyramidal-like neurons in the stratum oriens of Cornu ammonis 1 and Cornu ammonis 2 area of Proechimys

AbstractProechimys (Rodentia: Echimyidae) is a neotropical rodent of the Amazon region that has been successfully colonized in the laboratory and used for experimental medicine. Preliminary studies indicated that Proechimys (casiragua) rodents express an atypical resistance to developing a chronic epileptic condition in common models of temporal lobe epilepsy. Moreover, previous investigation of our laboratory described a remarkably different Proechimy's cytoarchitecture organization of the hippocampal CA2 subfield. In the present study, we investigated the intrinsic neuronal properties and morphological characteristics of the Proechimys's hippocampal pyramidal neurons of the CA1 and CA2 areas. A comparative approach was performed using neurons recorded in Wistar rats. A striking finding in Proechimys rodents was the presence of large pyramidal-like neurons throughout the stratum oriens from CA2 to CA1 area. In order to confirm such distinctive feature of the Proechimys's hippocampus, we performed Nissl staining and immunohistochemistry for neurofilament protein SM311. CA2 pyramidal neurons in the stratum pyramidale of Proechimys exhibited a significantly higher input resistance and lower time constant when compared to corresponding cell groups in the same area of the Wistar rat's. This newly identified population of pyramidal-shaped neurons in stratum oriens of Proechimys exhibited distinct electrophysiological and morphological properties. This included larger capacitance, lower input resistance, larger rheobase, long latency to first action potential and slower firing frequency. In addition, the apical dendrites of these neurons were oriented in parallel to apical dendrites of regular pyramidal neurons in stratum pyramidale. Moreover, these neurons were immunoreactive to SM311 as the majority of the neurons of the pyramidal layer. The functional role of these hippocampal neurons of the rodent Proechimys deserves further investigation

Identifying the Sources of Ferromagnetism in Sol-Gel Synthesized Zn\u3csub\u3e1-x\u3c/sub\u3eCo\u3csub\u3ex\u3c/sub\u3eO (0 ≤ x ≤ 0.10) Nanoparticles

We have carefully investigated the structural, optical and electronic properties and related them with the magnetism of sol-gel synthesized Zn1-xCoxO (0 ≤ x ≤ 0.10) nanoparticles. Samples with x ≤ 0.05 were pure and free of spurious phases, whereas ZnCo2O4 was identified as the impurity phase for samples with x ≥ 0.08. Samples with x \u3c 0.05 were found to be true solid solutions with only high spin Co2+ ions into ZnO structure, whereas sample with x = 0.05, exhibited the presence of high spin Co2+ and low spin Co3+. For the impurity-free samples we found that as Co concentration increases, a and c lattice parameters and Zn–O bond length parallel to the c-axis decrease, the band gap drastically decreases, and the average grain size and distortion degree increases. In all samples there are isolated Co2+ ions that do not interact magnetically at room temperature, bringing about the observed paramagnetic signal, which increases with increasing Co concentration. M vs T curves suggest that some of these disordered Co2+ ions in Zn1−xCoxO are antiferromagnetically coupled. Moreover, we also found that the intensity of the main EPR peak associated to Co2+ varies with the nominal Co content in a similar manner as the saturation magnetizations and coercive fields do. These results point out that the ferromagnetism in these samples should directly be correlated with the presence of Co2+. Bound magnetic polaron model is insufficient to explain the Room temperature ferromagnetism in these Co doped ZnO samples and the charge transfer model seems not influence considerably the FM properties of Zn1-xCoxO nanoparticles. The FM behavior may be originated from a combination of several factors such as the interaction of high spin Co2+ ions, the formation of defect levels close to the valence band edge and grain boundaries effects