Laboratory studies determined that a decrease in the quality of potato foliage,Solanum tuberosumL., resulted in indirect competition between Colorado potato beetle,Leptinotarsa decemlineata(Say), and potato leafhopper,Empoasca fabae(Harris). Fitness of potato beetles decreased when they fed on potato plants damaged by potato leafhoppers. Potato leafhoppers produced fewer eggs on plants that had been partially defoliated by potato beetles or coated with excrement. Both species distinguished between damaged and undamaged foliage.