The rapid leaf-movement seen in Mimosa and Neptunia is fascinating because it is unusual among plants and its function is poorly understood. This seismonasty has been well documented and substantial physiological and anatomical costs, therefore there must be or have been a significant adaptive advantage of rapid leaf-movement. One hypothesis is that leaf-movement startles arthropods thereby reducing herbivory. We tested this hypothesis by comparing herbivore reaction to M. pudica, M. strigillosa, and N. lutea, species with different degrees of leaf-movement. We compared oviposition preference, larval preference and growth among the three plant species, and found that Eurema lisa (Lepidoptera: Pieridae) responded to the three species differently.
Significantly fewer eggs per plant, 25, were oviposited on the most reactive sensitive plant, M. pudica (F = 18.78, df = 2, P < 0.0001), while there was no significant difference in larval feeding preference between M. pudica and N. lutea (which had the highest number of eggs per plant, 116). Pupal weight was significantly larger when larvae were raised on N. lutea, but there was no statistical difference between M. pudica and M. strigillosa. Therefore, seismonasty appears to reduce oviposition on M. pudica, reducing herbivory on that plant.