Impact of Alfalfa Weevil Larval Feeding on the Quality and Yield of First Cutting Alfalfa

Larval feeding by Hypera postica (Gyllenhal) on first cutting alfalfa reduced both the yield and quality of the crop. A linear reduction in yield was observed over most of the population range. The amount of loss attributable to a single larva and the smallest larval density (SLD) that produced the maximum yield reduction was dependent upon the size of alfalfa plant during the time of attack. Larger plants were able to withstand larger larval densities. Associated with this yield change was a significant increase in yield at larval densities equivalent to 15–22% of the SLD value. A reduction in stem elongation occurred at a density of 30–100% of the SLD value. Quality (crude protein and in-vitro dry matter digestibility) losses were observed over most of the range with a significant increase occurring at a larval density equivalent to 25–35% of the SLD value.