Modification of Vip3Ab1 C-Terminus Confers Broadened Plant Protection from Lepidopteran Pests.

Vegetative insecticidal proteins (Vips) from Bacillus thuringiensis (Bt) are unique from crystal (Cry) proteins found in Bt parasporal inclusions as they are secreted during the bacterial vegetative growth phase and bind unique receptors to exert their insecticidal effects. We previously demonstrated that large modifications of the Vip3 C-terminus could redirect insecticidal spectrum but results in an unstable protein with no lethal activity. In the present work, we have generated a new Vip3 protein, Vip3Ab1-740, via modest modification of the Vip3Ab1 C-terminus. Vip3Ab1-740 is readily processed by midgut fluid enzymes and has lethal activity towards Spodoptera eridania, which is not observed with the Vip3Ab1 parent protein. Importantly, Vip3Ab1-740 does retain the lethal activity of Vip3Ab1 against other important lepidopteran pests. Furthermore, transgenic plants expressing Vip3Ab1-740 are protected against S. eridania, Spodoptera frugiperda, Helicoverpa zea, and Pseudoplusia includens. Thus, these studies demonstrate successful engineering of Vip3 proteins at the C-terminus to broaden insecticidal spectrum, which can be employed for functional expression in planta.

Discovery of the aryl heterocyclic amine insecticides: synthesis, insecticidal activity, field results, mode of action and bioavailability of a leading field candidate.

BACKGROUND: γ-Amino butyric acid (GABA) antagonists are proven targets for control of lepidopteran and other pests. New heterocyclic compounds with high insecticidal activity were discovered using a competitive-intelligence-inspired scaffold-hopping approach to generate analogs of fipronil, a known GABA antagonist. These novel aryl heterocyclic amines (AHAs) displayed broad-spectrum activity on a number of chewing insect pests. RESULTS: Through >370 modifications of the core AHA structure, a 7-pyrazolopyridine lead molecule was found to exhibit much improved activity on a number of insect pests. In field trial studies, its performance was 2-4 times lower than commercial standards and also appeared to be species dependent, with good activity seen for larvae of Spodoptera exigua, but inactivity on larvae of Trichoplusia ni. CONCLUSION: An extensive investigational biology effort demonstrated that these AHA analogs appear to have multiple modes of action, including GABA receptor antagonism and mitopotential or uncoupler activity. The limited capability in larvae of T. ni to convert the lead molecule to its associated open form correlates with the low toxicity of the lead molecule in this species. This work has provided information that could aid investigations of novel GABA antagonists. © 2016 Society of Chemical Industry.

Novel nicotinic action of the sulfoximine insecticide sulfoxaflor.

The novel sulfoximine insecticide sulfoxaflor is as potent or more effective than the neonicotinoids for toxicity to green peach aphids (GPA, Myzus persicae). The action of sulfoxaflor was characterized at insect nicotinic acetylcholine receptors (nAChRs) using electrophysiological and radioligand binding techniques. When tested for agonist properties on Drosophila melanogaster Dα2 nAChR subunit co-expressed in Xenopus laevis oocytes with the chicken ß2 subunit, sulfoxaflor elicited very high amplitude (efficacy) currents. Sulfoximine analogs of sulfoxaflor were also agonists on Dα2/ß2 nAChRs, but none produced maximal currents equivalent to sulfoxaflor nor were any as toxic to GPAs. Additionally, except for clothianidin, none of the neonicotinoids produced maximal currents as large as those produced by sulfoxaflor. These data suggest that the potent insecticidal activity of sulfoxaflor may be due to its very high efficacy at nAChRs. In contrast, sulfoxaflor displaced [(3)H]imidacloprid (IMI) from GPA nAChR membrane preparations with weak affinity compared to most of the neonicotinoids examined. The nature of the interaction of sulfoxaflor with nAChRs apparently differs from that of IMI and other neonicotinoids, and when coupled with other known characteristics (novel chemical structure, lack of cross-resistance, and metabolic stability), indicate that sulfoxaflor represents a significant new insecticide option for the control of sap-feeding insects.