Important life history traits of animals may parallel those of their food sources, a factor that plays out at multiple trophic levels, potentially influenced by sexual and temporal variation. Here I evaluate the role of three variables in a system featuring a pair of alternative host plants, a herbivore, and its principal primary parasitoid. My test system consists of the fern-feeding moth Herpetogramma theseusalis (Crambidae) and its principal enemy, the parasitoid wasp Alabagrus texanus (Braconidae), which depend on two distantly related host plants, sensitive Onoclea sensibilis (Dryopteridaceae) and marsh Thelypteris palustris (Thelypteridaceae) ferns. I measured the effects of host plant, sex and yearly variation on several aspects of the mass and development times of the moth and wasp on the two host plants. Although the timing of pupation and eclosion, and length of pupal period, varied from year to year, both the moth and wasp often varied in the same way on the two host plants, with faster development times offset by differences in size. However, intersexual differences in performance by both moth and wasp on time and size-related variables usually exceeded differences in performance on the two host plants, in spite of the sizeable phylogenetic distance between them. Despite their intimate relationship, moth and wasp responses to size and temporal variables differed in several instances, including pupation date, time as a pupa and conversion of pupal to adult biomass. In general, the moths responded more strongly than the wasps to these variables.