Effects of herbivory on internal ethylene production and sex expression inCucurbita texana

1. Field-grown Cucurbita texana was used in a study to determine if stress ethylene from damaged leaves promotes changes in sex expression. 2. Internal ethylene concentrations were experimentally enhanced by inserti ng an ethylene-filled syringe into the hollow chamber of an internode seven nodes from the growing tip of a branch. Branches enhanced with ethylene pr oduced significantly more pistillate buds than control branches and experie nced greater bud abortion later in floral development. 3. The timing and magnitude of Diabrotica beetle leaf damage was simulated using a paper-hole puncher (15% removed from all leaves). Simulated herbivo ry was applied to new growth every 3 days throughout the growing season. 4. Endogenous ethylene concentrations recovered from the internode adjacent to the growing tip were significantly greater in damaged plants than undam aged plants 1 day after damage to new growth during the second and third we ek of the experiment, and 2 days after damage during the fourth and fifth w eek. By the sixth week, no significant differences were evident. 5. Damaged plants produced fewer pistillate buds than undamaged plants, ind icating that stress ethylene from simulated herbivory does not induce femal eness. A second messenger that suppresses pistillate bud production may be produced during damage.