DISTRIBUTION AND DENSITY OF CARABID BEETLES (COLEOPTERA) IN A PEST MANAGEMENT APPLE ORCHARD

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Abstract
Two soil sampling techniques were used over a 2 year period to examine the distribution of carabid beetles in a pest management apple orchard in southern Ontario. Soil coring was the most suitable technique for investigating temporal and vertical distribution patterns. Horizontal distribution of individual carabid species was best examined by sampling the rhizosphere of the cover crop only. Comparison of the soil sampling results with those obtained from pitfall traps showed that in late summer carabid larvae are subterranean in habit, as are adults of Bradycellus rupestris Say and Amara spp. Carabid density was highest (289.1 m−2) in late summer and fall, and lowest in late winter. In most samples carabid density was greatest in the rhizosphere of the cover crop and decreased rapidly with increasing depth: few beetles were found at depths greater than 30 cm. In August, densities of the commonest adult carabids were greatest close to trees in the orchard and decreased with increasing distance from trees. The distribution of carabid larvae was not related to distance from the tree, but densities of larvae were higher to the south of trees, and lower to the north.