It seems like the eggs are laid early in the development of the pods,but that is just an assumption on my part based on the fact that one application of Sevin just after the flowers fade has been enuogh to prevent any problems here. Once the pods get bigger, their walls might be too tough for the grubs to bore through?
It also helps to peal away any spathe material that might be attached to the side of the pod. They provide hiding places for insects and, as Paul pointed out earlier I think, they can be a source of rot if the weather is wet enough
