Found this information in a grower's magazine and thought it might be helpful and informative when planting your spring garden.
"New studies conducted by USDA Agricultural Research Service horticulturalist Eric Brennan have shown better pest control when alyssum is planted near organic lettuce in certain formations. In particular, randomly planting alyssum between lettuce plants may be very effective for aphid control. The reason? The alyssum attracts a beneficial insect, the hoverfly. Hoverflies lay eggs nearby, then, once hatched, the larvae hop on over to the lettuce to prey on currant lettuce aphids."
- taken from "GrowerTalks Magazine," April 2014.