RESEARCH Science Biology

BIOLOGY
Insect bites on plants reduce photosynthesis, imaging device shows

Jim Barlow, Life Sciences Editor
(217) 333-5802; b-james3@uiuc.edu

1/17/02

Photo courtesy Evan DeLucia Undamaged Wild parsnip leaf under normal undamaged conditions.

CHAMPAIGN, Ill. — When insects feed on plants, they get nourishment and the plant gets damaged. The amount of damage has taken on new light, thanks to a new photosynthesis-measuring device that illuminates and photographs never-before-seen injury extending far beyond an insect’s bite.

Photo courtesy Evan DeLucia Damaged A wild parsnip leaf that has been damaged. Dark holes are where caterpillars have fed. The bluish discolored areas show how damage has extended out from the bite areas throughout the leaf.

The results of the first experiments with the tool – done in a University of Illinois laboratory using leaves of wild parsnip (Pastinaca sativa) and hungry cabbage loopers (Trichoplusia ni) – were published Jan. 15 on the online "early edition" of the Proceedings of the National Academy of Science.

Researchers found that damage to a leaf isn't relegated to a hole where tissue once was. In this case, it affects three to six times more of the leaf's surface. The images gathered clearly recorded blue halos, representing damage to patches of cells surrounding the insect-caused holes, and varying levels of red fluorescence, denoting precise reductions in photosynthesis activity. They also found an almost 80-fold increase in the synthesis of furanocoumarins, a defensive chemical, suggesting that a plant may purposely turn down its photosynthetic machinery to boost its defensive capacity.

"We don't know how our results will hold up in a real ecosystem, as we’ve only tested this instrument in a one plant-insect system under laboratory conditions," said Evan H. DeLucia, a UI professor of plant biology. "But this study does suggest that we are greatly underestimating the impact of herbivores on plants. In the past, we knew tissue was removed. Now we know that the impact in terms of lost carbon gain can be much greater than just the tissue loss."

In a normal year, losses in agricultural and forest systems to dining insects range from 2 percent to 24 percent. The loss in plant photosynthesis, however, could be much greater and have potential management implications if carbon dioxide levels increase as projected under global warming scenarios. The device is now being tested on UI-grown soybean plants and on trees in a North Carolina forest.

DeLucia pondered the periphery damage when he saw leaves riddled with holes as he walked in a forest. Without a means to measure photosynthesis-related changes, he consulted with Antony Crofts and Timothy J. Miller in the UI department of biochemistry and Kevin Ox borough, a plant physiologist and computer programmer at the University of Essex in the United Kingdom.

With funding to DeLucia from the Illinois Critical Research Initiatives program, they built the device and teamed with UI entomologists May R. Berenbaum and Arthur R. Zangerl, and Jason G. Hamilton, a biologist at Ithaca College in New York, to study caterpillar-caused damage to parsnips.

The prototype consists of a high-speed camera linked to specially designed parallel processing computers. The camera sits in a colander-shaped light source containing more than a thousand high-intensity light-emitting diodes. A momentary flash of bright light hits a leaf's surface, and the computers instantaneously collect data, providing high-resolution images.