On 08/02/2016 21:03, Mathew Newton wrote:
I may well give another treatment at the end of summer, following hatching of eggs laid by those I've missed, to hopefully remove this factor from the equation for next winter...

Leatherjackets are the larvae of craneflies. They don't lay eggs
themselves - they have to emerge as adults, and then the adults lay
eggs. They aren't doing it in this weather.

If you can keep the adults off somehow you won't have a problem next
year. I wouldn't be surprised to find the nematodes persist for a while
at least - or else how do they survive outside the lab & garden?

Andy