Insecticidal Toxins

We are interested in a variety of toxins that act either in the gut or within the hemocoel of the insect that have potential for use in insect pest management. 

Insect-specific neurotoxins

A wide variety of venomous species produce toxic peptides that are specific for insects. These toxins represent an untapped resource for insect pest management due to the lack of an appropriate system for delivery of the toxins from the insect gut to their target site within the hemocoel (body cavity) of the targeted pest. We recently demonstrated that the coat proteins of plant viruses (luteoviruses) when fused to such toxins, effectively deliver the toxins into the hemocoel of aphids resulting in suppression of damaging aphid populations.

Figure: A few hemocoelic toxins are orally active and can cross the gut epithelium, while most require a delivery system to reach their target sites within the insect hemocoel. Recombinant baculoviruses and recombinant entomopathogenic fungi have been used for toxin delivery. Luteovirus coat proteins and some lectins can serve as protein-based carriers.

Related papers:

Pal, N., Yamamoto, T., King, G.F., Waine, C., Bonning, B.C. 2013. Aphicidal efficacy of scorpion- and spider-derived neurotoxins. Toxicon 70:114-22.

Bonning BC, Pal N, Liu S, Wang Z, Sivakumar S, Dixon PM, King GF, Miller WA. 2014. Toxin delivery by the coat protein of an aphid-vectored plant virus provides plant resistance to aphids. Nat. Biotechnol. 32(1):102-5. doi: 10.1038/nbt.2753.

Bonning BC, Chougule NP. 2014. Delivery of intrahemocoelic peptides for insect pest management.Trends Biotechnol. 2013 Dec 11. pii: S0167-7799(13)00177-7. doi: 10.1016/j.tibtech.2013.08.001.

See Digital Repository @ Iowa State University to download related publications.

Bt toxins

Insect specific toxins derived from the bacterium Bacillus thuringiensis (Bt) have been extensively used for insect pest management. Such toxins can be delivered by the bacterium itself (for use in organic agriculture or for suppression of mosquito larvae for example), and via transgenic plants. As Bt is a soil bacterium with toxins detected on plant surfaces, toxins have evolved that kill herbivorous insects that chew on plant material. There has been no selection for Bt toxins that kill sap-sucking or hemipteran insects that feed on plant sap. The hemipteran pests present a particular challenge as chemical insecticides represent the only tool available for management.

We are working on several approaches to improve the toxicity of Bt-derived toxins against Hemiptera.  Using the pea aphid as a model system, we examined the physiological bases for the lack of toxicity of selected toxins.  We demonstrated that different toxins behave differently in the aphid gut with some being unstable, and others binding but exerting only low levels of toxic action.

Research on insect gut physiology to understand why toxins are or are not active when ingested led to a novel approach for retargeting of gut toxins to species that are not normally susceptible to a given toxin (see Chougule et al., 2013 below). This strategy combines our research on Bacillus thuringiensis-derived toxins with work on disruption of plant virus transmission (see Liu et al., 2010 below).  

With support from USDA NIFA, the Iowa Soybean Association and the Citrus Research & Development Foundation, we are currently adapting this strategy to target the pea aphid, A. pisum, the soybean aphid, Aphis glycines, and the Asian citrus psyllid, Diaphorina citri.

Related papers:

Liu, S., Sivakumar, S., Sparks, W.O., Miller, W.A., Bonning, B.C. 2010. A peptide that binds the pea aphid gut impedes entry of Pea enation mosaic virus into the aphid hemocoel. Virology 401 (1): 107-16

Li, H., Chougule, N.P., Bonning, B.C. 2011. Interaction of the Bacillus thuringiensis delta endotoxins Cry1Ac and Cry3Aa with the gut of the pea aphid, Acyrthosiphon pisum (Harris). J. Invertebr Pathology 107: 69-78.

Chougule, N.P. and Bonning, B.C. 2012. Toxins for transgenic resistance to hemipteran pests. Special issue of the online journal Toxins “Insecticidal Toxins” 4(6), 405-429 doi:10.3390/toxins4060405

Chougule, N.P., Li, H. Liu, S., Narva, K.E., Meade, T., Bonning, B.C. 2013. Retargeting of Bt toxins against hemipteran insect pests. Proc. Natl. Acad. Sci. USA

See Digital Repository @ Iowa State University to download related publications.