Abstract.1Generalist predators are repelled by chrysomelid (Chrysomelaspp.,Phratora vitellinueL.) larval defensive secretions that are obtained from salicin in their host plants. But little is known about the effect of these secretions on specialist predators.2In this study, we describe the feeding behaviour of a fly,Parasyrphus melanderiCurran (Diptera: Syrphidae), which feeds onChrysomela aeneicollisSchaeffer (Coleoptera: Chrysomelidae).Parasyrphus melanderilays its eggs onC.aeneicollisegg clutches, and its larvae consumeC.aeneicolliseggs and larvae.3Chrysomela aeneicollishatching rates were significantly lower (20%) on clutches with fly eggs than on clutches without them (40%). Half of the clutches with one fly egg had survival rates below 5%, and when two fly eggs were present (four clutches), the entire clutch was consumed.4In nature,P.melanderieggs were 3 times more abundant on a salicylaterich willow speciesS.oresteraSchneider, than on the medium‐salicylateS.geyerianaAnderss. (1.8v0.6 eggs per clutch). On 18% of theS.oresteraclones, all the beetle clutches contained fly eggs. In laboratory‐choice tests,P.melanderilarvae fed equally rapidly onC.aeneicollislarvae that were chemically defended (feeding onS.orestera) as on larvae that produced no secretion (feeding on the salicylate‐poorS.luteaNutt.). This predator does not appear to be deterred byC.aeneicollis'sdefensive secretion. We discuss the implications of specialist predators on determining host suitability to herbivorous in