If I am not mistaken those are the ones that live in to top soil? If so I had that issue once and I put a 1/2" to an inch of sand and then some fine small pebble rocks on the surface (as was mentioned above), they cant push through the sand and die out. The ones that were out I added fly strips and as others have said I bottom watered for a couple weeks problem went away. With the small layer of pebbles on the sand you can water from top so long as the sand stays put I am pretty sure but probably best to just water from bottom.