Insecticidal Activity and Synergistic Combinations of Ten Different Bt Toxins against <i>Mythimna separata</i> (Walker)

• Main Authors: Jing Yang, Yudong Quan, Prabu Sivaprasath, Muhammad Zeeshan Shabbir, Zhenying Wang, Juan Ferré, Kanglai He
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Toxins
• Subjects: <i>Bacillus thuringiensis</i>; Cry protein; Vip3 protein; oriental armyworm
• Online Access: https://www.mdpi.com/2072-6651/10/11/454
• ISSN: 2072-6651

The oriental armyworm (OAW), <i>Mythimna separata</i> (Walker), is a destructive pest of agricultural crops in Asia and Australia. Commercialized Bt crops have performed very well against their target pests; however, very few studies have been done on the susceptibility of OAW to Bt toxins in either sprays or expressed in Bt crops. In this work, we evaluated the toxicities of Cry1Ab, Cry1Ac, Cry1Ah, Cry1Fa, Cry2Aa, Cry2Ab, Cry1Ie, Vip3Aa19, Vip3Aa16, and Vip3Ca against OAW neonate larvae, as well as the interaction between Cry and Vip toxins. The results from bioassays revealed that LC₅₀ (lethal concentration for 50% mortality) values ranged from 1.6 to 78.6 &#956;g/g (toxin/diet) for those toxins. Among them, Vip3 proteins, along with Cry1A proteins and Cry2Aa, were the ones with the highest potency, with LC₅₀ values ranging from 1.6 to 7.4 &#956;g/g. Synergism between Cry and Vip toxins was observed, being high in the combination of Vip3Aa16 with Cry1 toxins, with synergetic factors ranging from 2.2 to 9.2. The Vip3Ca toxin did not show any synergistic effect with any of the toxins tested. These results can help in designing new combinations of pyramiding genes in Bt crops, as well as in recombinant bacteria, for the control of OAW as well as for resistance management programs.