Hay meadow, bottom land alfalfa is the chief factor in maintaining an aphid population since it is the principal overwintering host, allows heavy populations to build up in the spring, and carries the minimum late summer population. The several thousand acres of alfalfa planted for soil erosion control on the sides and gullies of the Blue Mt. ridges where the peas are grown contributes very little to aphid abundance, even though it provides succulent host plants scattered throughout the canning pea district at the time aphids migrate from hay meadow alfalfa. Early peas are also in a succulent stage of growth during the period that erosion control alfalfa is attractive as an aphid host. Since early peas are grown in large fields adjacent to the hay meadows they are more accessible to the aphids and usually support heavier populations. Both early peas and erosion control alfalfa produce aphids which later move to the main pea crop. Erosion control alfalfa is not essential to the migration cycle and its use has not aggravated the pea aphid problem.