Wednesday, November 15, 2006

Soybean N Relations and Bean Leaf Beetle Larval Feeding Damage.

Walter Riedell, Jonathan Lundgren, Shannon Osborne, and Joseph L. Pikul Jr. USDA-ARS, USDA-ARS North Central Agricultural Research Lab, 2923 Medary Ave., Brookings, SD 57006

This study was conducted to determine if soil fertilizer nitrogen (N) input treatments would impact the bean leaf beetle (Cerotoma trifurcate Förster) biology.  The experiment was conducted in the soybean [Glycine max (L.) Merr.] phase of a long-term corn (Zea mays L.) and soybean rotation study.  Soil N input treatments were: corn fertilized for a yield goal of 8.5 Mg/ha (high N input), 5.3 Mg/ha (medium N input), or corn not fertilized (no N input).  Corn and soybean plots also were treated with banded starter fertilizer (112 kg/ha)  as 14-16-11, 7-16-11, or 0-16-11 elemental N-P-K on the high N, medium N, and no N input treatments, respectively.  First generation larvae from the medium and no N input plots had significantly larger body size than larvae from the high N input plots.  Head capsule widths of first generation beetles from medium N input plots were significantly larger than beetles that emerged from the other N input plots.  Soybeans grown on high N input plots showed higher shoot nitrate-N concentration than plants grown on the no N input treatments.  Shoot ureide-N concentrations were not significantly different across N input treatments, which suggests that there were few differences in soybean root nodulation across soil N management treatments.  Because larvae are thought to feed upon root nodules, it was surprising to find significant soil N input treatment effects on bean leaf beetle larval characteristics.  Our research clearly shows that nitrogen inputs affected bean leaf beetle immature stages.  However, the mechanisms that may be mediating these effects are not readily apparent.

Handout (.pdf format, 139.0 kb)