These insects attack a wide array of plants causing a loss in vigor, leaf yellowing and defoliation, and in some instances severe distortion of the foliage. Aphids are small, soft-bodied, pearl-shaped insects that have a pair of cornicles (wax-secreting tubes). Aphids are sucking insects and as they feed on the plant, they excrete excess sap called honeydew. Sidewalks, cars, and patio furniture may become wet with honeydew. A sooty mold often grows on the sugars contained in the honeydew and blackens stems, leaves and any other surface. Aphids may transmit plant pathogens.