If you only see adult GVB in the crop then these adults have most likely flown in from nearby crops or undergrowth. In this case most Trissolcus releases should target the areas around the crop as well as crop margins.
If you also see immature stages of GVB in the crop then they are obviously breeding in crop as well so more wasps can be released in crop if there's not much insecticide spraying.
The tell tale sign that Green Vegie Bug eggs have been parasitised is that the eggs go black, instead of orange-red of unparasitised prior to hatching. The wasp will emerge about 10-14 days are parasitisation while unparasitised eggs yield bugs in about 6 days.
Monitoring for small green stink bug raspberries
The black eggs are parasitised. The pale coloured eggs have yielded bugs.
Trissolcus wasp parasitising small green stink bug egg..
Be on the look out for clusters of small brown eggs laid either on the ends of the calyx when fruit are half grow or else on the fruit.
Freshly laid GVB egg raft
5 day old GVB egg raft