Tritrophic interactions among linear furanocoumarins, the herbivore Trichoplusia ni (Lepidoptera: Noctuidae), and the polyembryonic parasitoid Copidosoma floridanum (Hymenoptera: Encyrtidae)
1996
Reitz, S.R. | Trumble, J.T.
Secondary plant metabolites can affect parasitoids directly or indirectly through their action on the parasitoid host. We assessed if the linear furanocoumarins, psoralen, bergapten and xanthotoxin, secondary plant metabolites present in Apium spp. and other taxa, exerted direct or indirect effects on Copidosoma floridanum (Ashmead), a polyembryonic parasitoid of Trichoplusia ni (Hubner), through diet incorporation bioassays. Because linear furanocoumarins are photoactivated, we tested for these effects in the presence and absence of UV radiation. Increasing concentrations of linear furanocoumarins prolonged larval development of T. ni, but resulted in greater pupal mass. Furthermore, increasing concentrations of linear furanocoumarins increased T. ni mortality, but only marginally. However, increasing concentrations of linear furanocoumarins in the host diet significantly increased mortality of the parasitoid. There were no significant differences in the number of reproductive parasitoid larvae among treatments, indicating that linear furanocoumarins did not interfere with polyembryonic development of C. floridanum, but exerted toxicity after the parasitoid larvae began feeding on host tissue. Supplemental UV radiation slowed development, but it did not affect survival of either T. ni or C. floridanum. Because of the differential effects on the host and parasitoid, linear furanocoumarins, at naturally occurring concentrations, can mediate this host-parasitoid relationship through direct effects on the parasitoid, and not merely as a consequence of their effect on the host.
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