Kelly S. Johnson, Ph.D.

     My research focuses on physiological and biochemical adaptations of herbivorous insects to their host plants. Insects feeding on plants are faced with the challenge of dealing with potentially toxic plant defensive chemicals while extracting enough nutrients from food material to maintain high growth rates.  One of my interests is in the isolation and description of novel plant products that have antifeedant, toxic or other biological activities towards insects.  Our lab has characterized bioactive phytochemicals from legumes (pyrrolizidine alkaloids in Crotalaria), osage orange (Maclura pomifera), and sweetbay magnolia (Magnolia virginiana).

     The primary emphasis of my work, however, is on the metabolic fate of plant nutrients and phytochemicals after they are ingested by an herbivore.  Insects have diverse adaptations for coping with plant chemical defenses, including behavioral avoidance of toxins, sequestration of compounds for antipredator defense, detoxification or target-site insensitivity.  Understanding the physiological and biochemical basis for such strategies contributes to our knowledge of ecological and evolutionary patterns of resource use by different insect taxa.  I am currently investigating low molecular weight phenolics, which are commonly involved in plant defense against herbivores. The biological activity of these compounds depends in part on oxidative activation; under oxidizing conditions, they can generate reactive oxygen species that damage membranes and proteins.  Unoxidized forms of the same compounds can have protective antioxidant functions.  I am using several caterpillar and grasshopper species to investigate how phenolic toxicity is affected by physicochemical conditions in the insect gut (pH, oxygen availability and oxidation-reduction potential) and the context of the diet with which they are ingested.

     Additional projects in the lab include investigations of the metabolic fate of pyrrolizidine alkaloids sequestered by the moth (Utet heisa ornatrix), phylogenetic patterns of gut pH and digestive proteinases in beetles, and responses of aquatic macroarthropods to stream acidification.

Selected References:

• Johnson, K. S. and G. W. Felton. 2001. Plant phenolics as dietary antioxidants for herbivorous insects: a test with genetically modified tobacco. J. Chem. Ecology (in press).

• Johnson, K. S. and G. W. Felton. 2000. Digestive proteinase activity in corn earworm (Helicoverpa zea) after molting and in response to lowered redox potential. Arch. Insect Biochem and Physiol.44:151-161.

• Johnson, K. S. and D. Rabosky. 2000. Phylogenetic distribution of cysteine proteinases in beetles: Evidence for an evolutionary shift to an alkaline digestive strategy in Cerambycidae. Comp. Biochem. and Physiol.B 126:609-619.

• Johnson, K.S. and R. V. Barbehenn 2000. Oxygen levels in the gut lumens of herbivorous insects. J. Insect Physiology. 46:897-903.

• Johnson, K. S. and G. W. Felton. 1999. (guest editors) Nutritional Physiology of Herbivorous Insects: Special Issue. Arch. Insect Biochem and Physiol. 1-99.

• Johnson, K.S. (1999) Comparative detoxification of plant (Magnolia virgininiana: Magnoliaceae) allelochemicals by generalist and specialist Saturnid silkmoths. J. Chemical Ecology 25:253-269.