Wise and colleagues caught a break when they observed that strong shade causes a ducking plant to become erect. They used this straightening response to test the "ducking hypothesis."
In a greenhouse experiment at Bucknell University in Pennsylvania, the authors used four sets of plants: ducking candy-cane plants grown in full sun, candy-cane plants with stems straightened by a shade treatment, erect plants grown in full sun, and erect plants grown in the shade treatment. The four sets of plants (128 total) were then randomized in a grid on a greenhouse bench, and the authors released adults of the goldenrod ball-gall-making fly, Eurosta solidaginis, amid the plants.
The results were striking. The flies did not lay an egg on a single ducking plant. However, they laid eggs on just as many straightened candy-cane plants as they did on both groups of erect plants. Because the straightened candy-cane plants completely lost their resistance, and because there were no differences between the straightened and nodding candy-cane stems other than ducking, the authors concluded that it is indeed the ducking that confers the resistance advantage.
The experiment also shed insight into why the gall flies did not lay eggs in ducking stems. Female flies were able to find the ducking plants well enough, but they seemed to be confused once they landed on a ducking plant. Wise suggests that the flies either do not see the apical leaf bud, or are confused by its upside-down orientation. "Rather than waste too much time, the flies leave the ducking plants to lay eggs on more accommodating hosts," Wise explains. He states that the next challenge is to figure out why, given their resistance advantage, ducking plants ar
|Contact: Richard Hund|
American Journal of Botany