They fly from miles it took 4 years for them to get from southern boulder to my house so its not something you can gain control on by just treating your property unless you got some serious serious space. It seems around 7 years after JBs show up they get some form of control reducing their numbers by say 80-90%?. Many people believe this is milky spore, although others think its beneficial nematodes and birds predating them also. Last year i convinced my paper wasps to start eating them by squeezing a bit of there guts out but not enough to kill them because wasps are jerks and like to eat food alive!
As you can imagine probably most all of us here other than the people with golf course lawn yards dry out pretty significantly. They dig deep in the soil and the clay protects them it seems. You are reading correctly that you need infected grubs to spread this fungal spore. Same way nematodes move around is by infecting a grub and then depositing tons of eggs later. The nematodes are not parasitic to us and some of the beneficial nematodes are parasitic to other parasites.
There are a few threads on them check em out
For cm you can do lures or beneficial nematodes and they get great control. CM also flies from far away and so poisoning them does little for next year or this year control, they do not get around the surround much at all. If you want unblemished fruit that will cover your bases