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New Plants Put a Hurt on Pests

By Linda McGraw
February 18, 1999

Plants designed to give insects a stomach ache may become an alternative to methyl bromide. This chemical pesticide, targeted as an ozone depletor, is now closely regulated and is scheduled to be phased out in 2005. The ban could mean about $1.5 billion in agricultural losses each year.

To create plants that more effectively fend off damaging insects, fungi and nematodes, Agricultural Research Service and Kansas State University researchers have added an insect enzyme to create insect-resistant transgenic tobacco and rice. The enzyme--chitinase--causes digestive problems for insects that ingest it.

ARS biochemist Karl J. Kramer at the Grain Marketing and Production Research Center in Manhattan, Kan., isolated the gene that codes for the chitinase enzyme from the tobacco hornworm, Manduca sexta. With Kansas State University plant molecular biologist Subbaratnam Muthukrishnan and plant pathologists Lowell Johnson and Frank White, Kramer cloned and incorporated this gene into the genetic material of tobacco and rice. ARS and KSU researchers have patented the only known insect chitinase gene used in transgenic plants.

Chitinase causes chitin, a key component in insect skin and gut tissue, to break down. This normally occurs when insects “shed their skin,” or molt. Chitinase puts a “chink in the armor” of the insect’s stomach by causing chitinous membranes to disintegrate. Without this membrane, insects are helplessly vulnerable to microbial infections.

In lab studies, the scientists found that the genetically engineered plants significantly suppressed the growth of feeding insect larvae.

Insect chitinase specifically targets chitin, making its presence in plants harmless to humans or animals. Several agricultural biotechnology companies are working with the scientists to transform other plants, such as corn, wheat and sorghum.

Scientific contact: Karl J. Kramer, ARS Grain Marketing and Production Research Center, Manhattan, KS, phone (785) 776-2711, fax (785) 537-5584,