Dr. Barbehenn received his Ph.D. from the University of California at Berkeley in 1989. His postdoctoral work was done with Professor Michael Martin in the Department of Biology at the University of Michigan.
Research areas in the Barbehenn lab have shifted over the decades between examining insect digestion and nutrition, peritrophic membranes, oxidative stress, phenolic compounds, antioxidants, and plant oxidative enzymes, back to insect nutrition. The nutritional quality of plants has a major impact on the fitness of insect herbivores. Caterpillar growth rates and body masses (fitness-related parameters) are generally greatest for larvae that feed on immature leaves. As leaves mature, their nutritional quality typically declines because of increased toughness and lower levels of some nutrients. We have recently discovered that protein availability can decline from mature leaves not only because of decreased protein levels, but also because of decreased protein extractability. Decreased protein extractability is largely responsible for the decline in protein assimilation efficiency by gypsy moth caterpillars on the mature leaves of red oak and presumably also on sugar maple (Barbehenn et al., 2013, 2014). Caterpillars on lush immature leaves assimilate protein with efficiencies of 70-80%, but this declines rapidly after leaf maturation, to efficiencies of less than 50%.
Surprisingly, in contrast to oaks and maples, the protein in poplars and other species in the Salicaceae remains highly digestible after their leaves mature! We wonder whether this pattern is telling us that there is a fundamental difference between the nutritional quality of “determinate” species (e.g., oaks and maples that cease growth after the spring leaves are produced) and “indeterminate” tree species (i.e., species that continue to produce leaves through the growing season). A major goal for our future research is to compare nutrient availability from mature tree leaves across a wide taxonomic range of species. Is there is a pattern of high protein extractability from indeterminate species? Are indeterminate species, therefore, more nutritious than determinate species after their leaves mature? What mechanisms would explain such a basic difference? The results of this work are expected to expand our understanding of nutritional ecology, host plant selection, and the evolution of host specialization in insect herbivores.