While Bill's comment on HSB not spawning in the pond is 99.9% correct, don't assume that they are sterile because they are not. The HSB just do not have the correct spawning habitat for the eggs to remain viable until they hatch.
esshup,
Have you ever heard (or read) of a successful spawn of HSB in a pond?
What is the limiting condition that defeats the spawning effort? Might someone's pond be close to favorable conditions?
