Senescing plants are not a favorable nutrition source for insects anymore, and so they look for overwintering locations. Plus the shorter days are another indicator to insects that they should protective shelter soon. But some insects are still trying to survive before the cold weather really hits.
Green stink bug nymphs feeding on nearly mature soybean. Photo by Mark Licht.
You may notice other insects attempting to feed on plants or the prey on plants until harvest. Usually those insects can't cause economic damage unless they are clipping pods or damaging corn kernels. But it is something to evaluate if the damage is throughout the field. Also take into consideration the pre-harvest interval of most insecticides is at least 21 days.
Are you seeing any late-season insect activity out there?