RESUMEN
En una finca ecológica (FE) y una convencional (FC) se comparó el comportamiento de poblaciones de babosas y su relación con algunos carábidos predadores, la presencia de arvenses, prácticas agrícolas y la productividad de cuatro variedades de lechuga (Lactuca sativa. L.). Semanalmente se realizaron capturas de babosas, conteos de nivel de daño, altura y número de hojas en 10 plantas. Se recolectaron arvenses y coleópteros en las dos fincas. Los conteos totales de babosas en la FE fueron estadísticamente superiores. Se colectaron cuatro especies (Deroceras. reticulatum, Milax gagates, Deroceras. laeve y Limax. maximux) frente a dos encontradas en FC. Con excepción de la variedad "Morada Lisa", no se encontraron diferencias significativas en el nivel de daño en las otras variedades entre las dos fincas, pero sí en la variable peso seco de FE. En FE se presentaron 5 especies de carábidos y 25 de arvenses frente a ninguna y 6 en FC, respectivamente. Los datos anteriores se explican en función de las prácticas agronómicas de cada sistema de manejo.
In an organic (FE) and a conventional (FC) farm system the population behavior of slugs and their relationship with some carabids predators was compared, as well as, the presence of weeds, agricultural practices and productivity of four varieties of lettuce. Weekly catches of slugs were made and the damage level, height and the number of leaves in ten plants was measured. Weeds and carabids were collected in both farms. The total number of slugs in the FE was statistically higher and four species (D. reticulatum, Milax gagates, D. and L. laev maximux) were collected compared with two found in FC. With the exception of the variety "Morada Lisa", there were no significant differences in the level of damage in the other varieties between the two farms. There were significant differences in the dry weight variable in favour of the organic farm. In FE, 5 carabids species and 25 weeds were presented compared to none in FC and 6, respectively. The data above are explained in terms of the agronomic practices of each management system.
RESUMEN
The role of carabid beetles in reducing populations of phytophagous insects has been an elusive subject. A field experiment was established on a commercial wheat crop (cv. Otto) with an area of 4.5 ha in Valdivia, Chile, during the spring and summer of 1996-1997. The field had been under a prairie system for two years, before wheat sowing (fertilization and a pesticide had been applied during crop development). Samples were taken at approximately monthly intervals. Carabid beetles were sampled with a grid of pitfall traps and other insects were sampled with a vacuum insect net and soil cores. The genera of the carabids found are of neotropical origin. Exclusion by polythene barriers, together with removal of carabid beetles using traps, was an effective technique for controlling carabid populations in a commercial wheat crop. A reduction in the number of carabid beetles was associated with an increase in the number of springtails and arachnids, and a decrease of agromyzid adults. Phytophagous insects, such as homopterans and lepidopterous larvae, were not affected by carabid exclusion and removal. The action of carabid beetles on the arthropod fauna can be extremely complex, due to its predatory activity at multitrophic levels.