Ecological Aspects of Insect Detoxication Enzymes and Their Interaction With Plant Allelochemicals

87 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.Inhibition of insect mixed-function oxidases (MFOs) by phytosynergists (plant compounds that synergize cooccurring toxins), differences in MFO activity and sensitivity to phytosynergists among insect species, and metabolic costs of MFO induction are investigated in a series of experiments.The plant compounds fagaramide, isosafrole, myristicin and safrole contain methylenedioxyphenyl (MDP) groups, inhibit MFOs (toxin metabolizing enzymes) and are phytosynergists of xanthotoxin, a cooccurring toxin. Myristicin is also a synergist of xanthotoxin phototoxicity in ultraviolet light.The MDP-containing benzylisoquinoline alkaloid berberine is more toxic than laudanosine, an alkaloid with similar structure but lacking an MDP group. This difference is not due to autosynergism by the MDP group of berberine because berberine is synergized by the MDP-containing compound, myristicin. Berberine is phototoxic but laudanosine is not. This probably results from phenyl groups conjugated in berberine but unconjugated in laudanosine.As a method of screening potential phytosynergists, twelve MDP-containing plant compounds were tested as inhibitors of MFOs in vitro and synergists of carbaryl in vivo. Phytosynergistic activity was positively correlated with in vitro inhibition but not correlated with in vivo synergism.MFOs in Heliothis zea were induced by indole-3-carbinol. Food utilization and growth parameters were used to measure metabolic costs of MFO induction. Three-fold to nine-fold induction of MFO activity produced no differences in any parameter, suggesting metabolic costs of induction are minimal.MFO titers were measured in papilionid larvae. The highest MFO titers were in Papilio polyxenes and P. cresphontes, which eat plants containing toxins and MFO inhibitors; the lowest titers were in Battus philenor, which sequesters toxins from its host plants for antipredator defense and thus does not metabolize the toxins with MFOs.Papilio polyxenes eats plants that produce both toxins and MDP-containing phytosynergists that inhibit insect MFOs, toxin metabolizing enzymes. MFOs from P. polyxenes are less sensitive to inhibition by MDP-containing phytosynergists than MFOs from two species that do not feed on toxins and phytosynergists, H. zea and Papilio troilus. This insensitivity may result from adaptation by P. polyxenes to plants that contain both toxins and phytosynergists.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD