|Tao, F - OKLAHOMA STATE UNIV|
|Giles, K - OKLAHOMA STATE UNIV|
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2005
Publication Date: June 1, 2006
Citation: Elliott, N.C., Tao, F.L., Giles, K.L., Kindler, D., French, B.W., Greenstone, M.H., Shufran, K.A. 2006. Ground beetle density in Oklahoma winter wheat fields. Southwestern Entomologist. 31(2):121-128. Interpretive Summary: Ground beetles (Carabidae) are important predators of pest insects in several crops. In Europe, where they have been extensively studied, ground beetles play an important role as part of a broader complex of predatory arthropods that biologically control cereal aphids in wheat and other cereals. Very little is known about ground beetles in winter wheat in Oklahoma and other Southern Plains states. We undertook this study to obtain basic knowledge of the species of ground beetles that occur in winter wheat fields, and how their abundance varies with respect to factors that might be important to their ecology, such as year, geographic location, and the density of cereal aphids. We found 21 species of ground beetle in Oklahoma winter wheat fields. The number of ground beetle species present in a field and their densities were not related to aphid population density in a field, indicating that ground beetles did not exhibit a numerical response to aphid populations. Absence of a relationship to aphid density would limit the effectiveness of ground beetles in biologically controlling cereal aphids, but does not necessarily indicate that they do not play an important role as part of the complex of natural enemies of cereal aphids. This is because ground beetles were present in the field early in the growing season and could therefore prey on cereal aphids early, while they are initially colonizing the field. Predation at that time could be particularly important in maintaining cereal aphid populations below economically damaging levels. Six species of ground beetle accounted for 65% of all ground beetles in wheat fields. Ground beetle densities in wheat fields in Oklahoma were variable among locations within the state, but were always low. Such low densities bring into question the extent to which ground beetles contribute to the biological control of cereal aphids and other pest insects in wheat in Oklahoma. Further research is desirable in Oklahoma and other Great Plains states to further elucidate the role of these predators in biological control of cereal aphids in wheat. Future studies should focus on the role in cereal aphid biological control of the species identified in this study as most abundant.
Technical Abstract: Ground beetles were sampled biweekly from four wheat fields, each located in a major wheat growing region of Oklahoma during the 1999-2000 and 2000-2001 growing seasons. The sample unit was a 0.5 m**2 circular frame embedded in the soil. Ten samples were taken in each field on each sampling occasion, and fields were sampled biweekly unless weather conditions precluded sampling. The area within the frame was sampled using a D-vac suction sampler followed by thorough hand searching within the frame of plants, the soil surface, and underneath loose soil. Aphids were also sampled in each field by inspecting 80 to 200 tillers and counting the number of aphids on each tiller. The average density of ground beetles across sampling dates and years ranged from 0.08 beetles per m**2 to 0.35 beetles per m**2 depending on location. Ground beetle community structure was not related to aphid population density in fields, indicating that ground beetles did not exhibit a numerical response to aphid populations. Six species, Agonum punctiforme Say, Amara impuncticollis Say, Bembidion castor Lindroth, Bembidion nigripes Kirby, Elaphropus dolosus LeConte, and Stenolophus conjunctus Say accounted for 65% of all ground beetles collected. Ground beetle communities varied in species composition and density among the four geographically separated winter wheat fields. Bembidion nigripes and B. castor were dominant species at all locations, but many other species varied markedly in occurrence and abundance among fields. Our study indicates that there are differences in ground beetle communities in wheat fields, but does not address whether these differences are related to regional or local differences in the environment. Ground beetle densities in wheat fields in Oklahoma were variable among locations, but were always low, averaging less than 1/2 beetle per m**2 during the growing season. Such low densities bring into question the extent to which ground beetles contribute to the biological control of cereal aphids and other pest insects in wheat in Oklahoma. Further research is desirable in Oklahoma and other Great Plains states to further elucidate the role of these and other generalist predators in biological control of insect pests of wheat.