The role of digestive proteases in the rotation-resistant phenotype of the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a significant insect pest of maize in the United States, Canada and Europe. Until the mid 1990s, this pest was successfully controlled by annual crop rotation, alternating maize with a non-host plant like soybean. However, massive adoption of maize-soybean rotation in east-central Illinois selected for a WCR phenotype that circumvents crop rotation by laying eggs outside of maize fields. This rotation-resistant variant of WCR (RR-WCR) display reduced fidelity to maize and is likely to fly into rotated soybean fields where it feeds and oviposits. When eggs laid in rotated soybean hatch the following spring, the emerging larvae now in a cornfield produce severe injury to maize roots. For the last fifteen years, other than behavioral characterization of the RR-WCR, establishing a correlation between genotypic and phenotypic attributes has proved elusive. Despite the ability of soybeans to produce defense compounds, RR adults are more frequently found feeding on soybean foliage than wild-type (WT) WCR. Soybean defenses against herbivory include cysteine protease inhibitors, which inhibit the activity of digestive proteases and impair the fitness of many coleopterans. The objective of this research was to determine whether RR-WCR adults display an altered digestive proteolysis that may increase their tolerance to soybean foliage diet and facilitate the occurrence of rotation-resistance. The results show that RR-WCR beetles had higher soybean intake and extended survivorship on continuous soybean diet. In addition, cathepsin L protease activity in RR-WCR populations was significantly higher than that of WT populations fed on either corn silks or soybeans. Gene expression analysis of cysteine proteases in WCR guts supports these findings; the expression level of a cathepsin L-like clone was significantly higher in RR-WCR adults when compared with WT populations. This thesis is the first report of eco-physiological, biochemical and molecular evidence supporting higher tolerance of soybean hervibory in RR-WCR. The discovery of a mechanism of tolerance to soybean herbivory in WCR offers unique information and tools to use in advancing understanding of the proximate mechanisms of insect adaptation to dietary stress.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Curzi, Matias J.

Contributors dc:contributor

• Seufferheld, Manfredo J.

• rotation resistance
• proteases
• western corn rootworm
• protease inhibitors

Statement dc:rights

• Copyright 2011 Matias J. Curzi

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/24403

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/24403