One egg is laid in each cell. As each larva is consumed, the woodpecker moves slightly to one side and repeats the drilling to obtain the next larva. The result is the long row of holes across the face of the plywood. The time for leafcutter be nesting is late spring though summer. We do not know how long after the bees complete the nest building that the woodpeckers begin the destructive search for food, but once the woodpeckers find the first bee, they quickly move down the line causing a significant amount of damage in a short period of time.
Damage is confined to the face of the plywood.
The bees do not tunnel or otherwise weaken the plywood - they utilize gaps that already existed. Woodpecker damage is usually confined the top and middle layers of the plywood. To my knowledge, there is no effective chemical control for this problem. The bees are a valuable part of the natural ecosystem and it would be unwise and impractical to control them by spraying plants where they forage. Woodpeckers are protected birds and cannot be legally killed.