Biological activities of the vegetative insecticidal protein Vip3Aa against beet armyworm (Spodoptera exigua)

Abstract

Vegetative insecticidal proteins (Vips) are produced by different bacterial species including Bacillus cereus and Bacillus thuringiensis during vegetative stage. They have broad spectrum toxicity against various pests including Lepidopteran. This study aimed to investigate the biological activity of Vip3Aa protein against beet armyworm (Spodoptera exigua). The 88.5-kDa recombinant Vip3Aa protein was produced in E. coli as a soluble protoxin. The purified Vip3Aa protoxin was processed by either trypsin or midgut proteases to yield a 62-kDa active toxin. At day 7 post feeding to the S. exigua 2nd instar lavae, the LC50 values of the Vip3Aa protoxin, the trypsin-activated Vip3Aa toxin, and the midgut proteases-activated Vip3Aa toxin were 556, 277, and 43 ng/cm(2), respectively. The midgut epithelial cells of the S. exigua 3rd instar larvae fed with Vip3Aa protoxin for 1 and 2 days were observed under scanning electron microscope (SEM). The epithelial cells were found swollen, misshaped, and lysed.