Figure 2. Weed biomass as a function of herbicide rate and Colorado potato beetle (L. decemlineata) herbivory in four greenhouse trials. Herbivory level is the number of larvae maintained on plants for the duration of the trials and mean observations are identified as 0 larvae in filled circles, 5 larvae in open circles, 10 larvae in filled triangles, 15 larvae in open squares (C and D only), 40 larvae in open triangles (A and B only). Equation 1 was fit to all observations within each L. decemlineata herbivory level and parameter estimates are reported in Table 2. Within each trial, similarity in dose response functions among herbivory levels was tested using the extra sum of squares principle for nonlinear regression. Herbivory levels followed by the same letter in parentheses are similar (F − test, α = 0.05).