UVM Theses and Dissertations
Format:
Print
Author:
Zhao, Yiwen
Title:
Dept./Program:
Plant and Soil Science
Year:
2009
Degree:
MS
Abstract:
Bacillus thuringiensis (Bt) is a species of insect-parasitic bacteria that has been developed as a microbial insecticide and widely applied in modem agriculture. In this study, we focused on the non-target effects of MON863 (YieldGard @ Rootworm) on the soil microarthropod community, therefore exploring the potential ecotoxicological risk of Bt to agricultural ecosystems. MON863 is a corn hybrid modified genetically to express a variant of the Cry3Bb1 protein which protects crops against corn rootworm complex Diabrotica spp. In 2003, three corn hybrids (transgenic MON863; isogenic non-transgenic hybrid treated with a soil insecticide for rootworrn control as a conventional management; and isogenic hybrid without insecticide as a genetic control) were planted in a no-tillage field in Maryland. A field experiment was conducted and designed as a Latin Square to account for variation in slope and soil type. Each treatment was replicated three times and the whole experiment was repeated in 2004 on adjacent plots without prior history of transgenic crops.
Soil samples were collected three times per year (pre-plant, mid-season, post-harvest), and the following year in May (pre-plant) to determine the duration of any non-target effect. Samples were collected repeatedly on the same experimental units. Mites and collembolans were extracted from soil by heptane flotation, then enumerated and identified by genera. Repeated measures analysis of variance was performed to identify differences among cultivar treatments across the entire growing season. Canonical correspondance analysis was employed to explore patterns among cultivars and taxa using soil moisture as a covariable. Compared with the genetic control, Bt corn did not have a significant negative effect on the microarthropod community. The tolerance of microarthropods to insecticide treatments differed by genera. A principal response curve analysis confirmed that treatment differences were consistent among years but patterns of seasonal fluctuation differed between growing season 2003-2004 and 2004-2005, with an inconsistent magnitude of difference in community composition. Based on the results, we conclude that MON863 corn is ecologically more sound than application of conventional insecticides for control of corn root worm.
Soil samples were collected three times per year (pre-plant, mid-season, post-harvest), and the following year in May (pre-plant) to determine the duration of any non-target effect. Samples were collected repeatedly on the same experimental units. Mites and collembolans were extracted from soil by heptane flotation, then enumerated and identified by genera. Repeated measures analysis of variance was performed to identify differences among cultivar treatments across the entire growing season. Canonical correspondance analysis was employed to explore patterns among cultivars and taxa using soil moisture as a covariable. Compared with the genetic control, Bt corn did not have a significant negative effect on the microarthropod community. The tolerance of microarthropods to insecticide treatments differed by genera. A principal response curve analysis confirmed that treatment differences were consistent among years but patterns of seasonal fluctuation differed between growing season 2003-2004 and 2004-2005, with an inconsistent magnitude of difference in community composition. Based on the results, we conclude that MON863 corn is ecologically more sound than application of conventional insecticides for control of corn root worm.