Abstract
Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is a major corn pest in the United States, causing annual losses of over $1 billion. One approach to protect against crop loss by this insect is the use of transgenic corn hybrids expressing one or more crystal (Cry) proteins derived from Bacillus thuringiensis. Cry34Ab1 and Cry35Ab1 together comprise a binary insecticidal toxin with specific activity against WCR. These proteins have been developed as insect resistance traits in commercialized corn hybrids resistant to WCR feeding damage. Cry34/35Ab1 is a pore forming toxin, but the specific effects of Cry34/35Ab1 on WCR cells and tissues have not been well characterized microscopically, and the overall histopathology is poorly understood. Using high-resolution resin-based histopathology methods, the effects of Cry34/35Ab1 as well as Cry3Aa1, Cry6Aa1, and the Photorhabdus toxin complex protein TcdA have been directly visualized and documented. Clear symptoms of intoxication were observed for all insecticidal proteins tested, including swelling and sloughing of enterocytes, constriction of midgut circular muscles, stem cell activation, and obstruction of the midgut lumen. These data demonstrate the effects of these insecticidal proteins on WCR midgut cells, and the collective response of the midgut to intoxication. Taken together, these results advance our understanding of the insect cell biology and pathology of these insecticidal proteins, which should further the field of insect resistance traits and corn rootworm management.
Highlights
Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is a major pest of maize (Zea mays) in the United States, causing annual losses of over $1 billion [1,2]
The midgut of WCR is composed of a simple columnar epithelium, with microvilli covering the apical region and a membranous labyrinth in the basal portion of the cell
The anterior midgut (AMG) region is immediately adjacent to the foregut, beginning just after the cardiac valve, and the cells of this region are generally very uniform in size and height such that the apical brush border forms a relatively smooth layer lining the lumen (Figure 1A)
Summary
Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is a major pest of maize (Zea mays) in the United States, causing annual losses of over $1 billion [1,2]. WCR eggs hatch in the soil during late spring, and neonate larvae immediately begin feeding on the roots of developing corn plants. Larval feeding damage to roots impairs water and nutrient uptake, results in corn lodging and reduced harvestability, and reduces overall crop yield. A highly effective means of controlling WCR crop damage in North America is planting transgenic corn hybrids expressing one or more crystal (Cry) proteins from Bacillus thuringiensis (Bt) [3]. The Bt crystal proteins currently available in commercialized Bt corn hybrids include Cry3Bb [4], mCry3Aa [5], eCry3.1Ab, and. Cry34/35Ab1 are the only commercialized insecticidal proteins not yet impacted by field-evolved WCR populations resistant to Cry3Bb1 maize.
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