ARTÍCULO
TITULO

Movement between crops and weeds: temporal refuges for aphidophagous insects in Central Chile

Cinthya M. Villegas    
Jaime A. Verdugo    
Audrey A. Grez    
Jaime Tapia    
Blas Lavandero    

Resumen

Crop edges have significant effects on populations of natural enemies, acting as source or sink habitats during the growing season. Previous observations have shown that coccinellid species are associated with thistle (Sylibum marianum (L.) Gaertn), a common exotic weed in the central valley of Chile. To determine whether thistles growing at crop edges act as a putative refuge for natural enemies, the seasonal relative abundance of aphidophagous coccinellids was estimated at 0, 10 and 25 m from the edges of three alfalfa fields. Mark-recapture studies were carried out using the trace element rubidium (Rb) to determine whether coccinellids moved between the edges and the alfalfa. The most common aphidophagous coccinellid species were Hippodamia convergens (63%), H. variegata (11%), Rhyzobius lophantae (4%) and Adalia angulifera (4%). In mid-November, the abundance of coccinellids at the edge of (0 m from the edge) the alfalfa plot increased compared to that at the center of the field (25 m from the edge), coinciding with a reduction in the population of aphids at all sampling points. Of the coccinellids captured at the thistle edge, 68% were marked with rubidium, suggesting movement of coccinellids from the alfalfa plot to the thistle growing at its edges. After the thistles were removed, coccinellids returned to the crop, as shown by the presence of marked coccinellids within the alfalfa fields at all three sampling distances. The results of this study suggest that thistles can act as a refuge for coccinellids when aphids are not available in the alfalfa fields.  Los bordes de los cultivos tienen efectos importantes sobre las poblaciones de enemigos naturales, pudiendo actuar como una fuente o sumidero durante la temporada de crecimiento. Observaciones anteriores sugieren que algunos coccinélidos estarían asociados con el cardo mariano (Sylibum marianum (L.) Gaertn), una maleza común en el valle central de Chile. Para determinar si estos bordes de cardo son posibles refugios de enemigos naturales, se estimó la abundancia de coccinélidos a 0, 10 y 25 m de distancia desde los bordes del cultivo en tres campos de alfalfa. Para estimar el movimiento de coccinélidos entre los bordes y la alfalfa, se llevaron a cabo estudios de marcaje-recaptura, usando el elemento traza rubidio (Rb). Los coccinélidos más comunes fueron Hippodamia convergens (63%), H. variegata (11%), Rhyzobius lophantae (4%) and Adalia angulifera (4%). A mediados de noviembre, la abundancia de coccinélidos incrementó al borde del campo de alfalfa (0 m), comparado con mediciones al centro del campo (25 m desde el borde), coincidiendo con una disminución de áfidos en todos los puntos de muestreo. Un 68% de los coccinélidos capturados al borde de los cardos estaban marcados con rubidio, lo cual sugiere el movimiento desde la alfalfa hacia los cardos de los coccinélidos. Después de la remoción de los cardos, los coccinélidos regresaron al cultivo, definido por aquellos coccinélidos marcados colectados posteriormente en la alfalfa en las tres distancias de muestreo. Se sugiere que los cardos pueden actuar como un refugio para estos depredadores cuando los áfidos no se encuentran disponibles en los campos de alfalfa.

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