Professor University of Colorado Boulder, Colorado
Some species of herbivorous insects utilize plant defenses as protection against predators by sequestration. Of these sequestering insects, their life history strategies can vary with regards to defense. For holometabolous insects, this can have implications for the final larval instar when preparing for metamorphosis. Junonia coenia (Nymphalidae) sequesters the plant secondary metabolites iridoid glycosides only in the larval life stages, whereas Euphydryas phaeton (Nymphalidae) sequesters and retains them through to adulthood. This variation may have implications for sequestration, but also for other defenses like immune function. Recent work suggests there is a trade-off between sequestration and immune function: sequestering higher amounts leads to lower immune function. Understanding how differences between two closely related species with contrasting life histories may affect this trade-off is important for understanding plant-herbivore and community interactions more broadly. Using J. coenia and E. phaeton as models, I presented caterpillars from three timepoints during their final larval instar (1, 3, and 5 days after molting) with either an single immune challenge or double immune challenge and monitored their sequestration and immune response using encapsulation measures and hemocyte counts.
Preliminary results show that sequestration does vary throughout the final larval instar for at least E.phaeton and that sequestration and hemocyte counts (one of the immune functions measured here) are negatively correlated.
