The relationship of plant size and age to herbivory and the effects of herbivory of two different insect species (grasshoppers and a root boring beetle) that feed on threadleaf snakeweed plants were examined on the Bernalillo watershed in New Mexico. These insects typically invade the southwest from May through September. Age structure and root borer damaged was measured by extraction of all threadleaf snakeweed plants (excluding seedlings) in 2, 8 x 8 m plots, canopy size (six size-classes), and presence of root borer damage were recorded. Mortality due to root boring beetle was measured by comparing live stems on 20 protected and 20 non-protected mature plants for a three year period. Juvenile plant mortality due grasshopper herbivory was determined by recording plant status (alive vs. dead) and presence or absence of herbivory on protected and unprotected plants. Mature protected and unprotected plants were examined for grasshopper herbivory, plant vigor and number of flower heads per plant was recorded.
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