Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato, Lycopersicon pennellii

Settling of the potato aphid, Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses of Lycopersicon pennellii, or of its F₁ with tomato, L. esculentum. The active compounds in the L. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 μg/cm². In choice assays, purified glucose esters from L. pennellii reduced aphid settling at concentrations as low as 25 μg/cm²; at concentrations of 150 μg/cm² or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 μg/ cm², these esters resulted in increased levels of mortality after 48 hr.