Chemical and thermal profile of Plectranthus amboinicus essential oil for its application as a bioherbicide

The species Plectranthus amboinicus is an aromatic herb with great application in popular medicine due to the diversity of biological properties. Chemically, its essential oil (EO) is characterized by two chemotypes, thymol and carvacrol, which vary depending on factors such as seasonality. Despite being an extensively exploited species, studies of the bioherbicidal potential of this species are insufficient. In this context, the EO of P. amboinicus leaves, extracted in two different seasonal periods, were characterized regarding chemical profile (by gas chromatography mass spectrometry - GC-MS) and thermal profile (DTG) and was subjected to bioherbicide tests (germination test and seedling development) against Eragrostis plana, commonly known as capim annoni, an invader of pastures in the Pampas region. P. amboinicus EO was a potent inhibitor of E. plana germination, reducing accumulated germination by over 70% when exposed to 0.1% EO, and a complete inhibition of germination was observed when exposed to 0.5%. Following the effects observed in germination, the initial growth of E. plana was significantly affected by concentrations above 0.05%. The major constituent identified via GC-MS was carvacrol, representing 87.5% of the volatile composition of P. amboinicus leaves. In addition, P. amboinicus EO presented high thermal stability up to 100 °C, which is an interesting result regarding its use as a bioproduct.

Regulaciones, políticas y conflictos por agroquímicos en Salta, Argentina

La consolidación del agronegocio en Argentina, desde finales del siglo XX, puede analizarse en sus múltiples y diversas consecuencias: impactos ambientales por la deforestación de bosques nativos; conflictividad social por la expulsión y destrucción de los modos de producción y reproducción de la vida campesina e indígena; efectos en la salud por la exposición a plaguicidas, entre los principales. A partir de fuentes de datos secundarias y de entrevistas en profundidad, el artículo busca aportar al entendimiento de las consecuencias ambientales y sanitarias ligadas al uso de agroquímicos en Salta, provincia del norte argentino que en años recientes incorporó amplias superficies a la producción agroindustrial. Se realiza una caracterización y análisis crítico de las normativas y políticas públicas en la materia, así como de las situaciones de conflicto. Los principales hallazgos muestran que en Salta existen leyes específicas que regulan el uso de agroquímicos y cierta institucionalidad destinada a su implementación y control. No obstante, el estudio releva una multiplicidad de situaciones que dan cuenta de la emergencia y trayectoria de conflictos que, con diverso grado de visibilidad e intensidad, problematizan los efectos en la salud humana y en los ecosistemas en las escalas locales. Abstract The consolidation of agribusiness in Argentina since the end of the 20th century can be analyzed in its multiple and diverse consequences: environmental impacts due to the deforestation of native forests; social conflict over the forcing out and destruction of rural and indigenous production and reproduction methods; health effects since exposure to pesticides, among the main ones. Based on secondary information sources and in-depth interviews, the article aims to contribute to the understanding of the environmental and sanitary impacts linked to fumigation with agrochemicals in Salta, a province of northern Argentina which in recent years has incorporated large areas into agricultural production and presents ecological and social characteristics that differ from the Pampas region. This research focuses on a critical characterization and analysis of the regulatory frameworks and public policies on that matter, as well as in a survey related to conflicts. The main findings show that in Salta different legal frameworks regulate the use of agrochemicals, while state agencies are meant to implement and monitor such regulations. However, the study compiles numerous situations that illustrate the emergence and path of certain conflicts that, with varying levels of visibility and intensity, problematize the effects on human health and ecosystems at the local levels.

Redefining the Distributional Boundaries and Phylogenetic Relationships for Ctenomids From Central Argentina

With about 68 recognized living species, subterranean rodents of the genus Ctenomys are found in a multiplicity of habitats, from the dunes of the Atlantic coast to the Andes Mountains, including environments ranging from humid steppes of Pampas to the dry deserts of Chaco region. However, this genus needs an exhaustive reevaluation of its systematic and phylogenetic relationships regarding the different groups that compose it. This knowledge is essential to propose biodiversity conservation strategies both at species level and at higher hierarchical levels. In order to clarify the taxonomy and the recent evolutionary history from populations of Ctenomys in the Pampas region, Argentina, phylogenetic relationships among them were evaluated using mitochondrial DNA sequences: gene encoding cytochrome b protein (1,140 bp) and the non-coding D-loop region (434 bp). To infer the divergence times inside the Ctenomys clade, a Bayesian calibrate tree using fossil remains data from different families within Caviomorpha was performed at first. Secondly, that calibration data was used as priors in a new Bayesian phylogenetic inference within the genus Ctenomys. This phylogenetic tree emphasized on species currently distributed on the Pampas region, more precisely considering both the talarum and mendocinus groups. Bayesian inferences (BI) were integrated with the results of a Maximum Likelihood approach (ML). Based on these results, the distributional limits of the mendocinus and talarum groups appear to be related to the physiognomy of the Pampas region soils. On the other hand, the validity of C. pundti complex as a differentiated species of C. talarum is debated. According to previous evidence from morphological and chromosomal studies, these results show a very low divergence between those species that originally were classified within the talarum group. Mitochondrial DNA sequences from populations associated with these putative species have not recovered as reciprocal monophyletic groups in the phylogenetic analyses. In conclusion, C. talarum and C. pundti complex might be considered as the same biological species, or lineages going through a recent or incipient differentiation process. The results obtained in this study have important implications for conservation policies and practices, since both species are currently categorized as Vulnerable and Endangered, respectively.

Behavioural Response in an Asilid Fly: Influence of Ecological and Environmental Factors on Spatial Density Dependence

Behavioural response of a parasitoid shows the effect on host parasitism patterns at a given host distribution resulting in an increase or decrease of parasitism intensity according to local host densities. This relationship could be proportional, positive, or negative, as a consequence of foraging of parasitoids searching for hosts. Mallophora ruficauda is a fly parasitoid of Cyclocephala signaticollis scarab beetle larvae and a predator of honeybees. Females search and place egg-clusters overground in open grasslands near beehives. Larvae actively searching for host underground following chemical cues arising from the host itself. The parasitism pattern is a result of this complex host-searching strategy which is shared between both stages of the fly. In this work we carried out a study at four spatial scales in apiaries located in the Pampas region of Argentina. We found that parasitism is inverse density-dependent at high female activity and direct density-dependent at low female activity at the larger spatial scale. We found a direct density dependent pattern associated to substrate height at intermediate spatial scale that is lost when the habitat has abundant oviposition substrates. Conversely, parasitism is inversely density-dependent at both smaller spatial scales, associated to oviposition substrate distance and saturation of healthy host by larvae attacking. Additionally, M. ruficauda does not select the oviposition substrates according to the abundance of Cyclocephala signaticollis inhabiting underground. This work shows the importance of a proper scale for analysis of factors that influence population dynamics and how environmental characteristics mould parasitism patterns in this dipteran parasitoid.

Soil compaction response to wheel traffic in the Rolling Pampas region of Argentina

The present work shows the effects of the different agricultural wheels traffic on the soil physical properties on a Typic Argiudoll soil worked under no-tillage cropping system. Soil compaction produced by traffic was quantified through these parameters: a) cone index, b) rut depth and c) soil water content at the traffic moment. Grain chaser, sprayer, harvester combine and tractor equipped with commonly used wheels in the study area were tested. The main results obtained showed that the tyres with the highest inflation pressure and tyre ground pressures produced the highest values of cone index and rut depth. Typic Argiudoll soil worked under continuous no-tillage cropping system is not able to constrain topsoil and subsoil compaction when it is wheeled by tyre with ground pressures greater than 77.6 kPa. Highlights Soil compaction causes a reduction in root growth and yield in many crops. Soil under a no-tillage system does not limit topsoil and subsoil compaction when wheeled by tyres with ground pressures greater than 77.6 kPa When the machinery load increases on soils with high bearing capacity (soils under a long-term no-tillage system), the subsoil compaction problems increase.