Entrapment of aphids and whiteflies in lettuce latex

Aphids and other insects alighting on lettuce inflorescences, Lactuca sativa L., often rupture latex canals causing latex exudation. I sought to determine how frequently aphids become trapped in exudate, how aphids release latex, and how lettuce parts compare in their propensity for trapping insects. For the last objective, I compared the survivorship and reproduction of aphids and whiteflies on the leaves, flower stalks (pedicels), bracts, and buds of black seeded Simpson lettuce. The two most abundant aphids on lettuce planted near Beltsville, MD, were Uroleucon pseudambrosiae (Olive) and Rhopalosiphum maidis (Fitch). Fully 79% of the U. pseudambrosiae and 98% of the R. maidis alates in my samples were physically glued to the lettuce plants, primarily by their legs. The aphids elicited latex release simply by walking across the plant surface. Alate U. pseudambrosiae females enclosed individually on lettuce bracts and buds suffered high entrapment rates and low survivorship, unlike females on stalks and leaves where entrapment rates were low and survivorship high. On the bracts and buds, the females produced fewer offspring; the nymphs often became mired in latex and died as a result. Overall, 71% of the trapped offspring perished during the 4-d test, whereas only 2% of the free offspring died. Some nymphs escaped entrapment by molting. Adult whiteflies, Bemisia tabaci (Gennadius), enclosed in cages on lettuce plants likewise became trapped in latex, primarily on the flower buds. My observations of thousands of trapped insects document the potency of canal-borne defenses and illustrate the effectiveness of plant adhesives in discouraging plant enemies.