Why are the adults more sensitive? Zinc concentrations above 139 ppb visibly affect wing pad development. Lower zinc concentrations may affect development in ways that are not visible or interfere with other structures. Deformed wing pads or other deformities can interfere with metamorphosis, a sensitive period with elevated mortality in mayflies. One of the ways that zinc may reduce mayfly populations is affects on successful molting.
J. S. Wesner, J. M. Kraus, T. S. Schmidt, D. M. Walters, and W. H. Clements. 2014. Metamorphosis Enhances the Effects of Metal Exposure on the Mayfly, Centroptilum triangulifer. Environmental Science & Technology.