Spatial fluctuations at vertices of epithelial layers: quantification of regulation by Rho pathway

In living matter, shape fluctuations induced by acto-myosin are usually studied in vitro via reconstituted gels, whose properties are controlled by changing the concentrations of actin, myosin and cross-linkers. Such an approach deliberately avoids to consider the complexity of biochemical signaling inherent to living systems. Acto-myosin activity inside living cells is mainly regulated by the Rho signaling pathway which is composed of multiple layers of coupled activators and inhibitors. We investigate how such a pathway controls the dynamics of confluent epithelial tissues by tracking the displacements of the junction points between cells. Using a phenomenological model to analyze the vertex fluctuations, we rationalize the effects of different Rho signaling targets on the emergent tissue activity by quantifying the effective diffusion coefficient, the persistence time and persistence length of the fluctuations. Our results reveal an unanticipated correlation between layers of activation/inhibition and spatial fluctuations within tissues. Overall, this work connects the regulation via biochemical signaling with mesoscopic spatial fluctuations, with potential application to the study of structural rearrangements in epithelial tissues.Comment: 8 pages, 3 figure

Acción de algunos acaricidas sobre los fítoseídos y la araña roja Panonychus ulmi (Koch) en manzano

Se han realizado 5 ensayos en manzanos para evaluar la acción de algunos acarici­das sobre la araña roja Panonychus ulmi (Koch) y sus depredadores los fitoseidos. En 4 ensayos la especie era Amblyseius andersoni (Chant) y en la otra A. californicus (McGregor). En total se han ensayado 14 materias activas. Se observa una mayor toxicidad de los productos sobre A. californicus que sobre A. andersoni, y en esta última especie la toxicidad suele ser mayor cuando el nivel de P. ulmi es más elevado. Las materias activas que son mas tóxicas para los fitoseidos son: amitraz, bifentrin y fenpropatrin. En el caso del amitraz se observa incluso una proliferación de P. ulmi. Los productos que son menos tóxicos para los fitoseidos y que dan una mayor relación depredador/presa, a pesar de su baja eficacia sobre P. ulmi, son: benzoximato, dioctil-sulfosuccinato-sodico y fenbutestan. Los acaricidas: cihexaestan, dinobuton, hexitiazox y propargita son medianamente tóxicos para los fitoseidos, pero su poca eficacia sobre P. ulmi provoca como resultado una relación depredador/ presa más baja que el testigo. Los que dan una mayor eficacia sobre P. ulmi, pero son más tóxicos para los fi­toseidos que los productos anteriores, por lo que dan como resultado unas relaciones de­ predador/presa más irregulares son: fenazaquin, fenpiroximato, piridaben y tebufenpirad. Deben realizarse más estudios sobre las dosis, mezclas y momentos de aplicación de todos estos productos para su utilización en el control integrado de la araña roja.Fourteen acaricides have been tested in five field trials to evaluate their efficacy on Panonychus ulmi (Koch) and their toxicity to the phytoseids Amblyseius andersoni (Chant) (4 trials) and Amblyseius californicus (McGregor) (1 trial). In general, the acaricides were more toxic to A. californicus than to A. andersoni. The toxicity to A. andersoni was higher when the population of P. ulmi was great. The more toxic to phytoseids active ingredients were amitraz, bifenthrin and fenpropathrin. An increase in P. ulmi populations was observed after the use of amitraz. The acaricides that gave a better predator/prey relationship were benzoximate, dioctil-sulfosuccinate and fenbutatin-oxide. This products showed the lowest toxicity to phytoseids but their efficacy against P. ulmi was low. The acaricides cyhexatin, dinobuton, hexythiazox and propargite were moderately toxic to phytoseids, but their low efficacy against P. ulmi led to a prey/predator relationship smaller than the observed relation in the control plots. The acaricides belonging to the METI-group (fenazaquin, fenpyroximate, pyridaden and tebufenpyrad) were the most efficient against P. ulmi, but also the most toxic to phytosedis, leading to irregular prey/predator relationships. More trials with this chemicals should be done to assess the correct rate, the mixtures betweend them, and the timing of application for use in IPM programs

Resultados de la aplicación en parcelas comerciales de un programa de control integrado de plagas de manzano en Lleida

Se describen los métodos de muestreo, los umbrales de tolerancia y los métodos de control utilizados en un programa de control integrado de plagas de manzano basado en el control biológico de Panonychus ulmi Koch mediante Amblyseius andersoni Chant y en el empleo de productos selectivos cuando existen, contra el resto de las plagas, en Lleida. El programa se ha llevado a cabo en 6 fincas en las campañas 1989-90 y 1990-91. Sólo en un caso no se produjo control biológico de P. ulmi, siendo necesario un tratamiento acaricida. En general, los métodos de control del resto de las plagas han funcionado correctamente, aunque en algunos casos son tácticas conservadoras. Se discuten finalmente los distintos componentes del programa de control integrado y se señalan los objetivos del plan de trabajo futuro.The sampling techniques, economic thresholds and control methods used in an IPM program for apples at Lleida (NE of Spain) based on the biological control of Panonychus ulmi Koch by means of Amblyseius andersoni Chant and the application of selective agrochemicals, when available, against other pests are described. The program was applied in six orchards in 1989-90 and in four orchards in 1990-91. Only one acaricide treatment was neccesary one year in one orchard, biological control being successfull otherwise. In general, control techniques worked well, although sometimes the strategies are not enough selectives. The different components of the IPM program are discussed and the goals of future research, outlined