At the end of summer yellow jackets can begin to rob weak honey bee hives. The beekeeper can take several actions to discourage them. Read the article in the link below. You can also help your weak hives by re-installing the entrance reducer; limit the entrance to the 4 inch long opening. In addition you can put out several yellow jacket traps. These can be easily made by re-cycling a 2 liter plastic pop bottle. Cut an entrance hole near the top. Then add a little sugar water to the bottle. The yellow jackets are attracted by the sugar water, enter the bottle , and become trapped.