I once had a neighbor, Bruce, who had several apple trees which bore fabulous fruit each season. The apples made the best apple pies I'd ever tasted. However, one particular season Bruce had problems with ants climbing his apple trees to feed on the aphids. Aphids eat plants, become engorged with sugar, and then ants suck the sugar from the aphids. It's little wonder that ants protect aphids, even picking them up and moving them to more plump areas of the plant. Aphids serve as a constant source of sugar for ants.
Bruce's apple trees were literally infested with the ants, protecting the feeding aphids. His apple tree leaves were being consumed voraciously, endangering his apple crop for the season, and dashing my hopes for savoring a tasty apple pie.
One hot sultry morning found Bruce outside, shaking his apple trees. I walked over to where he worked, and watched. He shook one tree, picked up his daughter's thick sidewalk chalk, and drew a thick chalk line around the diameter of the tree trunk, about three feet up from the ground, and then placed a few worms on the tree branches. Bruce treated each tree in the same manner until he had performed this strange ritual on each one. I asked, "Bruce, what in the world are you doing?" He told me that he shook most of the ants from his trees and, since ants won't cross a chalk line, he drew the line so that the ants wouldn't climb the tree. What I thought were worms were actually lacewing larvae, which ate all of the aphids. It took about four days for Bruce to totally rid his apple trees of ants and aphids, and I was able to enjoy my tasty apple pie that season.
I learned that day that ants will not cross a chalk or powder line. Why? Because when ants travel, they leave a pheromone trail that can be followed by other ants. When you deposit chalk or powder across their trail, the pheromone path is broken, and then the ants will find another route. If you find ants around your home, draw a thick chalk line or a good portion of talcum powder around the foundation of your house, across door thresholds, along window sills, and anywhere you think ants would travel to get into your home. You can also chalk or powder your plants if you see ant activity, or even douse ant hills with several shots of talcum powder. The ants will lose the scent of the colony and move on to other areas.