Lygus species are a devastating pest to the alfalfa seed industry in Washington. Lygus feed on the buds of alfalfa plants, causing seed abortion. Broad-spectrum insecticides such as organophosphates have typically been used to control lygus, but due to new regulations many of these pesticides will no longer be available. A potential alternative to chemical use is biological control by generalist predators. Conservation of key predators may be effective at reducing losses caused by lygus bugs. Although biocontrol by generalist predators looks promising, the pea aphid, Acyrthosiphon pisum, is a very abundant alternative prey that could disrupt control of lygus. In a two year study, conducted from 2003 to 2004, alfalfa seed and hay fields were sampled every three to four weeks by suction sampling, pitfall sampling and visually counting arthropods on stems. With frequent sampling, pest and predator fluctuations could be monitored throughout the stages of alfalfa growth and development. The most common predators determined through sampling were used in a series of lab and field experiments. First no-choice Petri dish assays with pea aphids and lygus were used to determine the predation rate of each predator species on each prey. Then, in microcosm experiments we varied background pea aphid densities and measured changes in predation on lygus. Finally, in field experiments we compared the abilities of predator guilds, which varied in their species composition, to control lygus.