INSECT PHENOLOGY MEDIATED BY HOST-PLANT WATER RELATIONS.

Water relations of host plants modify Enchenopa binotata life histories by mediating the termination of egg dormancy, thereby promoting synchronization of egg hatch. Dormant eggs must undergo dehydration and subsequent hydration to begin development. Dehydration of eggs is brought about in the field by declining water levels in branches during the fall and by prolonged cold. Hydration of eggs occurs when sap begins to rise in early spring. Since the ascent of sap occurs at different times in the six species of Enchenopa host plants, the phenology of egg hatch and adult maturation are allochronic. Shifts to novel host plants differing in phenology promote asynchrony of Enchenopa life histories among host-plant species. Thus, the host plant acts as an extrinsic disruptive factor that may promote genetic divergence and temporal reproductive isolation in Enchenopa. © 1990 The Society for the Study of Evolution.