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Dear Stephen
Sorry, but I have no experience in collecting adults or rearing so I will quote Rudiger Wagner (1997) on this: "Life cycles are almost unknown....adults emerge during the entire year, when temperatures in the terrestrial environment are suitable....adults may be collected with a handnet and seem to swarm preferably at sunset. It may also be adequate to use an aspirator." rearing seems to be very difficult but Rudiger gives some hints on this: "...can be kept alive in petri-dishes on some wet substratum (leaves, mosses, liverworth etc.) at low temperatures (6-12 C). Sufficient aeration (circular incision in the cover, closed with plastic gauze!) is necessary. If the dishes are entirely closed, larvae will die of the high humidity."
perhaps you can even try an emergence trap in the water just above the water line were you have seen the larva.
Good luck.