Effects of linear furanocoumarins on the herbivore Spodoptera exigua and the parasitoid Archytas marmoratus: host quality and parasitoid success

We assessed the effects of three photoactivated linear furanocoumarins, secondary plant metabolites present in Apium spp. (Apiaceae) and other taxa, on the larval-pupal parasitoid, Archytas marmoratus (Townsend) (Diptera: Tachinidae) and the host Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), in the presence and absence of ultraviolet radiation. These results then were compared with previously described responses of Archytas marmoratus and other hosts to different plant allelochemicals. Ultraviolet radiation had no consistent detrimental effects. Increasing concentrations of linear furanocoumarins (from 0 to 0.029% of fresh weight) increased mortality of both the host and parasitoid. Increasing linear furanocoumarin levels also prolonged larval development of surviving S. exigua, but had no effect on pupal developmental time or pupal mass. Consequently, there was no effect of increasing linear furanocoumarin levels on surviving parasitoid development time (from the time of host pupation) or size. These results indicate the effects of linear furanocoumarins are mediated through effects on the host. Because reported responses of Ar. marmoratus to other allelochemicals (e.g., flavones, methyl ketones) are mediated through host effects, these results support the hypothesis that Ar. marmoratus displays a generalized response to plant allelochemicals that are predictable based on host mediated effects.