| Nematicidal seed treatments are a welcomed new tool to manage the soybean cyst nematode, Heterodera glycines, in soybean production. Results of field-based research on the effects of nematicidal seed treatments have been inconsistent and do not indicate how or when a seed treatment affects the nematode. This dissertation describes 1) the development of new methods to study H. glycines biology and 2) the use of new and traditional methods to study the effects of AvictaRTM (abamectin) and ClarivaRTM (Pasteuria nishizawae) seed treatments on the biology of H. glycines.;Two new methods were developed to study the behavior of H. glycines second-stage juveniles (J2s) exposed to abamectin. The first method utilized a high-resolution flatbed scanner that automatically recorded images of populations of H. glycines every hour for 24 hours. A custom computer program then compared the locations of the nematodes in the population from one image to the next to calculate the percentage of nematodes in the population that moved. The second analysis method recorded videos of individual H. glycines J2s after incubation in abamectin. Computer analysis of the videos tracked the motion of individual nematodes by measuring the speed and change in curvature of points along the nematode body. Both methods measured paralyzing effects of abamectin on J2 movement and motion at concentrations of 1, 10, and 100 microg/ml. Sequential digital imaging combined with computer analysis provided quantitative data unavailable in manual microscopic observation of nematodes.;Controlled-environment experiments combined new methods (including movement analysis) with traditional methods in the greenhouse and laboratory to discern the effects of Avicta and Clariva seed treatments on specific life stages and processes of H. glycines. The stages and processes analyzed included hatching, movement, penetration, development, and reproduction. As a seed treatment, Avicta, with the active ingredient abamectin, inhibited nematode movement and root penetration at soil depths 2 and 5 cm below the soil line. Clariva seed treatment, comprised of spores of Pasteuria nishizawae, inhibited juvenile movement, penetration at specific soil depths (2, 5, and 7 cm), and development in younger plants. Overall, both treatments were most effective when H. glycines were found outside the root and inside young plants (up to 20 days). Effects of either treatment were minimal in older plants (30 to 60 days) with larger root systems. Protection of younger plants early in the season, though, may still be sufficient to increase stand establishment and increase yield in H. glycines-infested soils. |
