The Bacillus thuringiensis δ-endotoxins (Bt toxins) are widely used insecticidal proteins in engineered crops that provide agricultural, economic, and environmental benefits. The development of insect resistance to Bt toxins endangers their long-term effectiveness. Here we have developed a phage-assisted continuous evolution selection that rapidly evolves high-affinity protein-protein interactions, and applied this system to evolve variants of the Bt toxin Cry1Ac that bind a cadherin-like receptor from the insect pest Trichoplusia ni (TnCAD) that is not natively bound by wild-type Cry1Ac. The resulting evolved Cry1Ac variants bind TnCAD with high affinity (dissociation constant Kd = 11-41 nM), kill TnCAD-expressing insect cells that are not susceptible to wild-type Cry1Ac, and kill Cry1Ac-resistant T. ni insects up to 335-fold more potently than wild-type Cry1Ac. Our findings establish that the evolution of Bt toxins with novel insect cell receptor affinity can overcome insect Bt toxin resistance and confer lethality approaching that of the wild-type Bt toxin against non-resistant insects.

/pdf/continuous-evolution-of-bacillus-thuringiensis-toxins-bptn5up095.pdf

Continuous evolution of Bacillus thuringiensis toxins overcomes insect resistance

The sap sucking insects (Hemiptera), which include aphids, whiteflies, plant bugs and stink bugs, have emerged as major agricultural pests. The Hemiptera cause direct damage by feeding on crops, and in some cases indirect damage by transmission of plant viruses. Current management relies almost exclusively on application of classical chemical insecticides. While the development of transgenic crops expressing toxins derived from the bacterium Bacillus thuringiensis (Bt) has provided effective plant protection against some insect pests, Bt toxins exhibit little toxicity against sap sucking insects. Indeed, the pest status of some Hemiptera on Bt-transgenic plants has increased in the absence of pesticide application. The increased pest status of numerous hemipteran species, combined with increased prevalence of resistance to chemical insecticides, provides impetus for the development of biologically based, alternative management strategies. Here, we provide an overview of approaches toward transgenic resistance to hemipteran pests.

https://www.mdpi.com/2072-6651/4/6/405/pdf

Toxins for transgenic resistance to hemipteran pests.

Genetically engineered crops help support conservation biological control

Facultative expression of alternative male morphologies is thought to allow individual males to select the phenotype with the highest fitness gain given their competitive status relative to other males with which they compete for females. Choice of, or switching between, morphs commonly relies on developmental threshold responses. Evolutionary changes in developmental threshold responses are thought to provide an important avenue for phenotypic diversification and the evolution of morphological and behavioral novelties. However, the extent to which alternative male phenotypes and their underlying threshold responses actually evolve in natural populations is unclear. Likewise, the ecological factors that shape the evolution of threshold responses in natural populations are unexplored for most organisms, as are the consequences of such modifications for patterns of morphological diversity. I examined the ecological basis of rapid threshold evolution in exotic populations of the horn-polyphenic dung beetle Onthophagus taurus. Male O. taurus vary continuously in body size as a function of larval feeding conditions. Only males that exceed a critical threshold body size develop a pair of long horns on their heads, whereas males below this threshold remain hornless. Populations in two exotic ranges of this species, the eastern United States and western Australia, have diverged in the mean threshold body size, which has resulted in the evolution of highly divergent and novel horn length--body size allometries in these populations. Populations in a third and previously unstudied exotic range of O. taurus in eastern Australia exhibit threshold body sizes roughly intermediate between the eastern U.S. and western Australian populations. I tested three hypothesis to explain how differences in ecological and demographic factors can drive allometric divergences between populations, using data derived from comparative, standardized sampling of a large number of populations in each exotic range. Results suggest that differences in the intensity of both intra- and interspecific competition have contributed to the evolution of divergent thresholds in these populations. My results do not support the hypothesis that shifts in threshold body sizes to larger body sizes are a consequence of increases in the mean body size of competing males. I discuss my results in the context of Onthophagus mating systems and the evolutionary implications of threshold evolution. Copyright 2003.

/pdf/the-behavioral-ecology-of-threshold-evolution-in-a-4vvl6ep106.pdf

The behavioral ecology of threshold evolution in a polyphenic beetle

Cross-order and cross-phylum activity of Bacillus thuringiensis pesticidal proteins.

The plant bugs Lygus hesperus Knight (Hemiptera: Miridae) and L. lineolaris (Palisot de Beauvois) have emerged as economic pests of cotton in the United States. These hemipteran species are refractory to the insect control traits found in genetically modified commercial varieties of cotton. In this article, we report the isolation and characterization of a 35 kDa crystal protein from Bacillus thuringiensis, designated TIC807, which causes reduced mass gain and mortality of L. hesperus and L. lineolaris nymphs when presented in an artificial diet feeding assay. Cotton plants expressing the TIC807 protein were observed to impact the survival and development of L. hesperus nymphs in a concentration-dependent manner. These results, demonstrating in planta activity of a Lygus insecticidal protein, represent an important milestone in the development of cotton varieties protected from Lygus feeding damage.

https://bioone.org/journals/Journal-of-Economic-Entomology/volume-105/issue-2/EC11207/Cotton-Plants-Expressing-a-Hemipteran-Active-Bacillus-thuringiensis-Crystal-Protein/10.1603/EC11207.pdf

Cotton plants expressing a hemipteran-active Bacillus thuringiensis crystal protein impact the development and survival of Lygus hesperus (Hemiptera: Miridae) nymphs.

A novel Bacillus thuringiensis crystal protein exhibiting insect inhibitory activity is disclosed. Growth of Lygus insects is significantly inhibited by providing the novel crystal protein in Lygus insect diet. Polynucleotides encoding the crystal protein, transgenic plants and microorganisms that contain the polynucleotides, isolated peptides derived from the crystal protein, and antibodies directed against the crystal protein are also provided. Methods of using the crystal protein and polynucleotides encoding the crystal protein to control Hemipteran insects are also disclosed.

Hemipteran and coleopteran active toxin proteins from Bacillus thuringiensis

Additional Records of Adventive Onthophagus Latreille (Coleoptera: Scarabaeidae) in North America

La presente invention concerne une nouvelle proteine cristalline de Bacillus thuringiensis presentant une activite inhibitrice contre les insectes. Le developpement des insectes Lygus est significativement inhibe par l’incorporation de la nouvelle proteine cristalline dans l’alimentation de l’insecte Lygus . L’invention concerne egalement des polynucleotides codant pour la proteine cristalline, des plantes et des microorganismes transgeniques qui contiennent les polynucleotides, des peptides isoles derives de la proteine cristalline, et des anticorps diriges contre la proteine cristalline. L’invention concerne egalement des procedes d’utilisation de la proteine cristalline et des polynucleotides codant pour la proteine cristalline afin de lutter contre les insectes hemipteres.

Stephen R. Penn

Papers

Cotton plants expressing a hemipteran-active Bacillus thuringiensis crystal protein impact the development and survival of Lygus hesperus (Hemiptera: Miridae) nymphs.

Hemipteran and coleopteran active toxin proteins from Bacillus thuringiensis

Additional Records of Adventive Onthophagus Latreille (Coleoptera: Scarabaeidae) in North America

Nouvelles protéines toxiques actives contre les hémiptères et les coléoptères issues de bacillus thuringiensis

Hemipteran- und coleopteran-aktive toxin-proteine aus bacillus thuringiensis