Extension Ag Update
July/August 2007
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Plant-herbivore Interactions and the Omics-es: The Future of Hyphenated Research?

May Berenbaum, Ph.D., Professor and Head of the Department of Entomology., University of Illinois

Appearances notwithstanding, insects actually do have a few things in common with humans; among these is an appetite for, and dependence upon, plants as food. The ways in which insects and humans go about the business of eating plants, however, differ dramatically.

Humans are spectacularly broad with respect to their intake of plant food; in a single day, a person can consume representatives of dozens of plant families. In contrast, insects are staggeringly narrow in their food plant choices; over 90 percent of all herbivorous insects feed on three or fewer plant families and in many species larval development is completed on a single species. Insects do share with humans an ability to metabolize plant toxins via cytochrome P450 monooxygenases, heme-based enzymes that are responsible for a broad range of oxidative reactions.

The dietary challenges imposed on insect P450s are fundamentally different from the dietary challenges imposed on human and other vertebrate P450s. Genome sequencing has provided an embarrassment of riches with respect to P450 inventories of both insects and plants; elucidating function, while presenting daunting operational challenges, promises to provide new insights into the process by which plant-feeding insects have come to be the most abundant multicellular organisms in terrestrial ecosystems

Nitrate and Chloride in the Illinois River Basin

Walt Kelly, Groundwater Geochemist, Center for Groundwater Science

A two-year investigation was conducted to investigate the sources and fate of nitrate (NO3-) and chloride (Cl-) in the Illinois River Basin. Water samples were collected on 13 occasions from 14 locations, nine in the Illinois River, two in the Des Plaines River, and one each in the Sanitary & Ship Canal, Fox River, and Sangamon River. Samples of potential sources, including treated wastewater (TWW), road salt runoff, precipitation, and tile drain water, were also collected.

Waterways in the Chicago area (i.e., the Des Plaines River and the Sanitary & Ship Canal) had relatively high concentrations of nitrogen species and NO3- isotopic data indicative of TWW. Downstream of Chicago, the isotopic signature shifted as increasing amounts of agriculturally derived nitrogen entered the river. The TWW signature was evident downstream at least as far as Pekin during most of the year and to the Mississippi River during low flow. There is isotopic evidence that denitrification is occurring in Peoria Lake during periods of low flow, with about half of the NO3-N load lost in August 2005.

Discharge of TWW and road salt runoff in the Chicago area have led to increased levels of Cl- in the river. Chloride concentrations in the Illinois River ranged from 40 to 488 mg/L; river water unaffected by human activities would be expected to have concentrations ≤ 15 mg/L. Chloride concentrations in river water spiked during the late winter and early spring as a result of road salt runoff, primarily in the Chicago region. A large component of Cl- in the Illinois River throughout the year was attributed to TWW from the Chicago area. Agricultural activities which dominate land use in the watershed downstream from Chicago appear to be primarily causing dilution of road salt and TWW. Chloride concentrations in the Illinois River at Peoria have been increasing with time; the annual median increased from about 20 mg/L in 1946 to near 100 mg/L in 2005. While median Cl- concentrations are well below the secondary drinking water standard (250 mg/L), periodic spikes (maximum measured in 2003 was 904 mg/L) may be harmful to freshwater biota.