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Title: PREDATOR ABUNDANCE IN ALFALFA FIELDS IN RELATION TO APHIDS, WITHIN-FIELD VEGETATION, AND LANDSCAPE MATRIX

Author
item Elliott, Norman - Norm
item KIECKHEFER, ROBERT - USDA-ARS RETIRED
item MICHELS, GERALD - TEXAS AGRIC EXP STN
item GILES, KRISTOPHER - OKLAHOMA STATE UNIVERSITY

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2002
Publication Date: 4/1/2002
Citation: ELLIOTT, N.C., KIECKHEFER, R.W., MICHELS, G.J., GILES, K.L. PREDATOR ABUNDANCE IN ALFALFA FIELDS IN RELATION TO APHIDS, WITHIN-FIELD VEGETATION, AND LANDSCAPE MATRIX. 2002. ENVIRONMENTAL ENTOMOLOGY. V. 31(2). P. 253-260.

Interpretive Summary: This study examined whether the abundance of aphid predators in alfalfa fields is dependent on aphid density in individual alfalfa fields during the growing season and among geographically separated alfalfa fields. We also examined how the abundance of predators was influenced by the landscape surrounding an alfalfa field and the vegetation within it. Predator abundance during the growing season in individual fields was dependent on abundance of aphids. There was no evidence of a relationship to aphids. Variables describing the composition and heterogeneity of the landscape surrounding alfalfa fields and the vegetation within fields were more influential than aphid abundance when predator abundance was examined for geographically separated fields. We conclude that features of the habitat and landscape play an important role in determining aphid predator abundance in alfalfa fields. The number of aphid predators available to colonize an agricultural field varies as a result of population processes occurring in the adjacent landscape. Vegetation structure within fields further modifies the number of predators within fields. These effects can overshadow the direct response by predators to their aphid prey. The importance of the research lies in the observation that the composition of the landscape and the agricultural field itself are as important as the availability of prey in determining aphid predator abundance in agricultural fields. The results suggest that biological control of aphids can be improved by conservation of natural enemies directed at habitat manipulation within agricultural fields and in the landscape surrounding the fields.

Technical Abstract: This study determined whether aphid predators exhibit a numerical response to aphid density in individual alfalfa fields during the growing season and among geographically separated alfalfa fields. We also determined how the abundance of predators in alfalfa fields was influenced by the landscape surrounding a field and the vegetation in it. When patterns of aphid and predator abundance were analyzed on the basis of variation within individual fields during the growing season, there was an aggregative numerical response by Hippodamia convergens, and by Chrysoperla plorabunda, but not by other Coccinellidae or the common damsel bug, Nabis americoferus. There was a reproductive numerical response by most coccinellids, but not by C. plorabunda or the N. americoferus. When patterns of predator and aphid abundance were compared for geographically separated fields, there was no aggregative numerical response by any of the predators, nor was there a reproductive numerical response. Variables describing the composition and heterogeneity of the landscape surrounding alfalfa fields and the vegetation within fields entered into stepwise regression models for predator abundance in fields more frequently than aphid abundance. We conclude that features of the habitat and landscape play an important role in determining aphid predator abundance and distribution in space. The size and species composition of the pool of aphid predators available to colonize a field varies as a result of population processes occurring in the adjacent landscape. Vegetation structure within fields further modifies predator numerical response to aphids. These effects can overshadow the aggregative and reproductive numerical response by predators to aphids in alfalfa fields.