microbiology, Vol 142, 1551-1556, Copyright © 1996 by Society for General Microbiology
The ribosome-inactivating protein restrictocin deters insect feeding on Aspergillus restrictus
T Brandhorst, PF Dowd and WR Kenealy
J. Whittier Biologics, Madison, WI 53711, USA.
The fungus-feeding beetle, Carpophilus freemani, consumed equal quantities
of young mycelia, fewer phialides bearing mature spores and much fewer
phialides bearing developing spores of Aspergillus restrictus compared to
those of Aspergillus nidulans when tested in diet choice assays. The degree
to which specific fungal structures were consumed was inversely related to
the localization of high levels of restrictocin, a ribosome-inactivating
protein, to those structures. Pure restrictocin added to the insect diet at
1000 p.p.m. killed 38.5% of C. freemani larvae and 62.5% of Spodoptera
frugiperda larvae in 48 h, but did not affect C. freemani adults or
Helicoverpa zea larvae over the same interval. In diet choice assays, 1000
p.p.m. of restrictocin deterred feeding by adult C. freemani and Sitophilus
zeamais compared to control diets. Thus, restrictocin production and
localization may have a natural defensive role against insect feeding at
times critical to spore formation by A. restrictus, and may have potential
as an insect control agent.
