BioLure, a synthetic food attractant for Mediterranean fruit fly [Ceratitis capitata (Wiedemann) ], is composed of three chemicals (ammonium acetate, trimethylamine hydrochloride, and putrescine). We deployed these components together and in separate MultiLure traps across predominantly native forests, non-native forests, farmlands, orchards, and residential areas on the islands of Hawaii and Maui, to evaluate attraction of C. capitata and nontarget insects. Large numbers (as many as 186 per trap per day) of mainly saprophagous nontarget flies (primarily Drosophilidae, Chloropidae, Lonchaeidae, Neriidae, Otitidae, and Calliphoridae) were attracted to BioLure. Very few predators, parasitoids, or pollinators were attracted. Native species, predominantly drosophilid and calliphorid flies, were attracted in large numbers in endemic forests, but mostly (at least 88%) introduced species were collected in orchards, backyards, and non-native forest. A comparison of attraction to the three separate components versus combined components in traps revealed that ammonium acetate and, to a lesser extent, putrescine are the key components attractive to nontarget species. Omitting the putrescine ingredient from BioLure did not drastically decrease C. capitata catches but reduced nontarget captures by 20%.