I do not trust the Green Beetle. No reason he couldnt have been programmed to act the way he does by the Reach, even to the point of believing what he is saying. In this way he could fool Miss Martan. I also found it odd that a green martian didnt react a bit more to the white martian reveal since they are supposed to truely distrust one another. I believe his reprogramming of the scarab is going to have it revert to its original programming at the crucial moment of the reach invasion.