Effects of diversity on beneficial and pest arthropods

Dunbar, Mike
Major Professor
Aaron J. Gassmann
Matthew E. O'Neal
Committee Member
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Vegetational diversity within agroecosystems can vary in in three basic ways; the species richness of plants, the spatial arrangement of species and the temporal relationship among species. Agroecosystems with greater vegetational diversity are associated with decreased pest abundance and increased natural enemy abundance. The objectives of this dissertation were to test the effect of farming practices that alter vegetational diversity on beneficial arthropod communities and pest insects. Farming practices investigated included the addition rye cover crop (Secale cereale L.) to corn (Zea mays L.) and the use of extended crop rotations.

Two separate studies were conducted on experimental plots to compare the effects of the addition of a rye cover crop and extended crop rotations against practices that lacked diversity on epigeal and canopy, beneficial arthropod communities. In both studies we hypothesized that practices that increased vegetational diversity would positively affect beneficial arthropods. Only modest differences were observed in the composition and abundance of beneficial arthropods with the addition of a rye cover crop and none were detected among crop rotations with different lengths.

Two on-farm studies were conducted to quantify the effects rye cover crop and the use of extended crop rotations on insect pests of corn. Farming practices, corn root injury and abundance of Diabrotica spp. were compared among cornfields that differed in the frequency of crop rotation and previous pest injury. Root injury and abundance of Diabrotica spp. were similar among cornfields, however, fields that had a history of crop rotation required significantly fewer pest management inputs. In the second study, the abundance of early season insect pests and injury to corn were compared between fields with and without a rye cover crop. Although adult moths were captured around all cornfields, significantly greater abundance of Mythimna unipuncta and greater proportion of defoliated corn were found in fields where corn followed a rye cover crop.