Figure 3. Choice behavior of beetles in the Y-tube olfactometer.

In a series of olfactometer experiments with Cerotoma ruficornis (A,B) and Gynandrobrotica guerreroensis (C,D), shoots of mature lima bean plants (A,C) and young entire plants (B,D) were used. The seven setups tested were: JA-induced plants (I; the four tested JA concentrations were 1.0, 0.1, 0.01, and 0.001 mmol L⁻¹) and herbivore-induced (HI, induced by G. guerreroensis) vs. control plants (sprayed with water instead of JA). As controls, beetles were given the choice to select between an empty olfactometer arm and control plants (0∶C) as well as between two empty olfactometer arms (0∶0). Bars represent means ± SE of percentage decisions made by each sex of beetles. The number of beetles tested in the different setups is indicated for each gender. Every beetle was subjected to the same experimental setup 8 times and the proportions of decisions were used for further analyses. Asterisks at the left side of the columns represents significant differences in percentage decisions between both odor sources according to Mann-Whitney U-test (* = P<0.05; ** = P<0.01; *** = P<0.001). Asterisks at the right side of the columns represent significant differences in choice behavior between male and female beetles according to Wilcoxon signed-rank test (* = P<0.05; ** = P<0.01; *** = P<0.001).