Specialist herbivores are linked to their host plants through a variety of mechanisms from oviposition cues, to cues to feed on the host the larval herbivore finds itself, to non-tolerance of a host once feeding is initiated. In order to examine the diet breadth of the Giant Swallowtail, Papilio (=Heraclides) cresphontes, in south Florida, I examined survival and development time of larvae to pupation on both the host plants on which eggs were laid and of an alternate host plant that I switched eggs to. Giant Swallowtails range from North America through northern South America, where they specialize on the family Rutaceae. There were three control groups (larvae raised on their natal host plant): Casimiroa edulis, Zanthoxylum fagara, and Z. coriaceum, hereafter referred to CE, ZF and ZC. There were two treatment groups: ZF to CE, and ZC to ZF. Survival in the control groups was either nearly complete (CE and ZF) or an utter failure (ZC). In the treatment groups, survival was complete on ZC, and nearly complete on CE. Among larvae in the control groups, larvae raised on CE took significantly less time to develop than that raised on ZF. When I switched eggs from ZF to other plants, the mean number of days to develop reflected that change. Eggs switched to CE pupated after a time intermediate to those raised on a natal plant of ZF or CE. It is interesting to note that the longest development time is that of larvae switched to a palatable plant (ZF) from one they fail to accept as a host (ZC). Additionally, while CE is exotic in Florida, its range includes other portions of the Giant Swallowtail's range. It appears that host plant usage in the Giant Swallowtail is genetically determined, likely as a result of all three mechanisms.

Key words: Casimiroa edulis, diet breadth, feeding trials, Giant Swallowtail, Rutaceae, Zanthoxylum fagara