Troutnut Forum > Fly Fishing Discussion > Mayflies: subimago to imago .... ?, Page 2

Perhaps some efficient predator eats the winged stages. Those individuals that released eggs the soonest would be selected "for." This is because those that tend to deposit eggs later in life never make it that far and are selected "against." Those that live reproduce and pass on their genes.

Although all female mayflies are evidently sexually mature
as subimagos and male subimagos possess mature gametes, males evidently
are never reproductively mature as subimagos, i.e. male subimagos cannot
mate. We have never found fully formed male genitalia, including the femaleclasping
forceps, in subimagos of any species. The male genitalia grow in a
paurometabolous fashion rather than being prepackaged like legs and wings,
and this may be a major factor in restricting mating to male adults.
The fact that adult properties have not been incorporated into the male
subimago so that the final molt might be eliminated may be due to some
incompatability of the hydrofuge function with possible emergence function
and the mate-capturing and copulating function. If such incompatibility exists
we cannot account for it, particularly in view of some other aquatic insects
that combine the roles in the ultimate instar. We must continue to assume that
two molts from the larval stage are required for males to attain reproductive
maturity and function. Thus the subimago has at least some necessary role in
transformation.