Feeding behavior of the green peach aphid, Myzus persicae (Sulzer), differed on Lycopersicon pennelli (Corell) D Arcy (LA 716) and ‘VFT Vendor’ tomato ( L. esculentum [Mill.]). Fewer aphids initiated feeding on L. pennellii (LA 716), and time to first probe was significantly greater. Also, percentage of time spent probing and number of probes were less on this accession of L. pennellii . Time to first probe was significantly greater, while percentage of time spent probing and number of probes were less on L. pennellii (LA 716) than on L. penllellii (LA 1912), an accession that lacks acylsugar production. There were no significant differences between the behavior of the aphids on L. pellnellii (LA 1912) and L. esculentum for time to first probe or percentage of time spent probing. The effect of acylsugars obtained from L. pennellii (LA 716) on settling of M. persicae was determined by feeding-cage experiments. In choice tests, the proportion of aphids that settled on a treated port was a decreasing function of application level of acylsugars, with a maximal effect at application levels of 50 mg acylsugars per square centimeter and greater.