About

Bruce Tabashnik is a Regents' Professor and Department Head of Entomology at the University of Arizona. His research focuses on the evolution and management of insect resistance to transgenic plants. He is involved in advancing understanding of how insects develop resistance to genetically modified crops and developing strategies to manage and mitigate this resistance, contributing significantly to the field of entomology and insect science.

Research topics

• Biology
• Agronomy
• Botany
• Horticulture
• Genetics
• Biotechnology
• Medicine
• Veterinary medicine
• Zoology
• Microbiology
• Ecology

Selected publications

• Evaluating cross-resistance and synergy between Vip3Aa and Cry proteins from Bt in six strains of Helicoverpa zea derived via F2 screens

  Crop Health · 2026-04-09

  articleOpen access

  Abstract Transgenic crops producing insecticidal Bacillus thuringiensis (Bt) proteins have revolutionized the control of some pests. However, the evolution of resistance by pests has reduced the efficacy of Bt crops. Pest resistance to Bt crystalline (Cry) proteins has spurred a shift to crops that produce the Bt vegetative insecticidal protein Vip3Aa together with Cry proteins. With widespread field-evolved practical resistance of the major pest Helicoverpa zea (corn earworm or bollworm) to Cry proteins in the United States, Vip3Aa is the only Bt protein in transgenic corn and cotton that is highly effective against many populations. We generated five strains of H. zea with > 100-fold resistance to Vip3Aa in a susceptible genetic background using F 2 screens of field populations from Louisiana, Mississippi, and Texas followed by crosses to a susceptible strain and additional laboratory selection with Vip3Aa. The results from diet bioassays show that in these Vip3Aa-resistant strains, cross-resistance to Cry1Ab, Cry1Ac, Cry1A.105, Cry1Fa, and Cry2Ab was not consistent and ranged 1100-fold: from 16-fold negative cross-resistance to 65-fold positive cross-resistance. By crossing a Vip3Aa-resistant strain with a Cry-resistant strain followed by selection with both types of Bt protein, we generated a strain highly resistant to Cry1Ac, Cry2Ab, and Vip3Aa. Cry1Ac and Cry2Ab interacted synergistically with Vip3Aa against this triple-resistant strain, such that combinations of the Cry proteins and Vip3Aa caused higher mortality than expected from their individual toxicity. The observed synergy may increase the durability of Bt crops producing combinations of these proteins against H. zea .

  PublisherOA PDFDOI

• Rootworm resistance to Bt associated with increased injury to corn pyramids combining Bt proteins and RNA interference

  Proceedings of the National Academy of Sciences · 2025-09-18 · 2 citations

  articleOpen access1st authorCorresponding

  Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have revolutionized pest management, but their benefits have been reduced by evolution of practical resistance in at least 31 cases. To delay evolution of resistance, farmers have shifted from crops producing one Bt protein to crops called pyramids that produce two or more Bt proteins or other traits targeting each pest. Here, we focus on resistance to transgenic corn pyramids in the western corn rootworm ( Diabrotica virgifera virgifera ) and northern corn rootworm ( Diabrotica barberi ), which cost farmers in the United States $2 billion yearly in yield losses. We analyzed 998 relevant data values for 2005 to 2023 from 12 published field studies. The results support the hypothesis that rootworm resistance to Bt proteins Cry3Bb and Gpp34/Tpp35Ab reduces the efficacy of pyramids that produce one or both of these proteins and an RNA interference trait (DvSnf7) targeting rootworms, despite no apparent strong cross-resistance between the Bt proteins and DvSnf7. The reduced efficacy of pyramids producing Bt proteins and DvSnf7 entails increased root injury and emergence of adult beetles. Efficacy of DvSnf7 was substantially lower for reducing root injury than emergence. Because root injury decreases yield, the increased root injury has immediate practical consequences. More sustainable control may be achieved by deploying pyramids with traits that are each highly effective against rootworms, increasing the abundance of host plants that do not target rootworms, and combining transgenic corn with crop rotation and other control tactics in integrated pest management programs.

  PublisherDOI

• Knockout of chitin synthase gene confers resistance to Bt toxin <scp>Vip3Aa</scp> in <i>Helicoverpa zea</i>

  Pest Management Science · 2025-09-21

  article

  BACKGROUND: Genetically engineered crops that produce insecticidal proteins from Bacillus thuringiensis (Bt) have many benefits and are used globally to manage key insect pests, including Helicoverpa zea (Lepidoptera: Noctuidae), a major pest of crops in the Americas. However, pests of at least 11 species, including H. zea, have evolved resistance to Bt crops, diminishing their effectiveness and benefits. For H. zea in the United States, practical resistance to Bt corn and cotton producing crystalline (Cry) Bt proteins is widespread and early warning of resistance to the vegetative insecticidal protein Vip3Aa has been reported. Thus, a better understanding of the genetic basis of resistance to Vip3Aa is needed to monitor, manage and counter resistance. In some strains of lepidopteran pests, resistance to Vip3Aa is associated with disruptive mutations in the chitin synthase 2 (CHS2) gene but this association had not been investigated previously in H. zea. RESULTS: Here, we show that mutations introduced by CRISPR/Cas9 editing of the CHS2 gene can cause resistance to Vip3A in H. zea. Disruptive mutations in CHS2 facilitated the creation of strain CHS2-KO that had 29 000-fold resistance to Vip3Aa relative to its unedited parental susceptible strain. Resistance to Vip3Aa in CHS2-KO was autosomal, recessive, and did not cause cross-resistance to Cry1Ac or Cry2Ab. CONCLUSION: Results of this study indicate that CHS2 plays an important role in Vip3Aa intoxication in H. zea. It will be important to determine if mutations in CHS2 contribute to field-evolved resistance to Vip3Aa in H. zea and other pests. © 2025 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

  PublisherDOI

• Editing the kinesin-12 gene affects responses to Bt toxin Cry1Ac in Helicoverpa zea

  Scientific Reports · 2025-11-26

  articleOpen access

  Crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) are used globally to manage key insect pests. However, the evolution of resistance to Bt proteins in at least 11 pest species has reduced the effectiveness of Bt crops. Resistance to crystalline (Cry) Bt proteins including Cry1Ac produced by Bt cotton is a major problem in Helicoverpa zea (also known as bollworm and corn earworm), one of the most economically damaging pests in the United States. A previous genome-wide association study identified a nonsense point mutation in a kinesin-12 gene that was associated with resistance to Cry1Ac in a lab-selected strain of H. zea. Here, we used CRISPR/Cas9 gene editing to knock out the kinesin-12 gene in a Cry1Ac-susceptible laboratory strain, which caused a 4.0-fold increase in resistance to Cry1Ac. Conversely, gene editing that repaired the natural kinesin-12 nonsense mutation in a lab-selected resistant strain increased susceptibility to Cry1Ac by 3.8-fold. These complementary results provide compelling evidence that kinesin-12 plays a role in the mode of action of Cry1Ac against H. zea.

  PublisherOA PDFDOI

• In memoriam: Ward Watt (1940–2024)

  Evolution · 2025-05-13

  articleOpen accessSenior author

  at the age of 84, after a stellar career deciphering the mysteries of evolution written on butterfly wings that first intrigued him as a boy (Fig. 1).His rigorous empirical work on biochemistry, physiology, behavior, and ecology elucidated how natural selection in the wild acts on genetic variation to drive adaptive evolution.

  PublisherOA PDFDOI

• Functional redundancy in the toxic pathway of Bt protein Cry1Ab, but not Cry1Fa, against the Asian corn borer

  Proceedings of the National Academy of Sciences · 2025-04-17 · 10 citations

  articleOpen accessCorresponding

  Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been used extensively to control some major crop pests, but their benefits decrease when pests evolve resistance. Better understanding of the genetic basis of resistance is needed to effectively monitor, manage, and counter pest resistance to Bt crops. Resistance to Bt proteins in at least 11 species of Lepidoptera, including many important crop pests, is associated with naturally occurring mutations that disrupt one or more of three larval midgut proteins: cadherin and ATP-binding cassette proteins ABCC2 and ABCC3. Here, we determined how CRISPR/Cas9-mediated mutations disrupting cadherin, ABCC2, and ABCC3 singly and in pairs affect resistance to Bt proteins Cry1Ab and Cry1Fa in the Asian corn borer ( Ostrinia furnacalis ), which is the most damaging pest of corn in Asia and is closely related to the European corn borer ( Ostrinia nubilalis ), a major pest in Europe and North America. The results from bioassays of six knockout strains and their parent susceptible strain support a model in which Cry1Ab can kill larvae via one path requiring ABCC2 or another path requiring cadherin and ABCC3, whereas Cry1Fa uses only the first path. The model’s predictions are generally supported by results from genetic linkage analyses and responses to Cry1Ab and Cry1Fa of Sf9 cells and Xenopus oocytes modified to produce cadherin, ABCC2, and ABCC3 singly or in pairs. The functional redundancy identified here for Cry1Ab could sustain its efficacy against O. furnacalis and may exemplify a widespread natural strategy for delaying resistance.

  PublisherDOI

• Proactive resistance management for sustaining the efficacy of RNA interference for pest control

  Journal of Economic Entomology · 2024-05-15 · 11 citations

  articleSenior author

  Biopesticides based on RNA interference (RNAi) took a major step forward with the first registration of a sprayable RNAi product, which targets the world's most damaging potato pest. Proactive resistance management is needed to delay the evolution of resistance by pests and sustain the efficacy of RNAi biopesticides.

  PublisherDOI

• Negative association between host plant suitability and the fitness cost of resistance to <i>Bacillus thuringiensis</i> (Bacillales: Bacillaceae)

  Journal of Economic Entomology · 2024-04-11 · 5 citations

  articleSenior author

  Transgenic crops producing Bacillus thuringiensis (Bt) toxins are commonly used for controlling insect pests. Nearby refuges of non-Bt host plants play a central role in delaying the evolution of resistance to Bt toxins by pests. Pervasive fitness costs associated with resistance, which entail lower fitness of resistant than susceptible individuals in refuges, can increase the ability of refuges to delay resistance. Moreover, these costs are affected by environmental factors such as host plant suitability, implying that manipulating refuge plant suitability could improve the success of the refuge strategy. Based on results from a previous study of Trichoplusia ni resistant to Bt sprays, it was proposed that low-suitability host plants could magnify costs. To test this hypothesis, we investigated the association between host plant suitability and fitness costs for 80 observations from 30 cases reported in 18 studies of 8 pest species from 5 countries. Consistent with the hypothesis, the association between plant suitability and fitness cost was negative. With plant suitability scaled to range from 0 (low) to 1 (high), the expected cost was 20.7% with a suitability of 1 and the fitness cost increased 2.5% for each 0.1 decrease in suitability. The most common type of resistance to Bt toxins involves mutations affecting a few types of midgut proteins to which Bt toxins bind to kill insects. A better understanding of how such mutations interact with host plant suitability to generate fitness costs could be useful for enhancing the refuge strategy and sustaining the efficacy of Bt crops.

  PublisherDOI

• Retrotransposon-mediated disruption of a chitin synthase gene confers insect resistance to Bacillus thuringiensis Vip3Aa toxin

  PLoS Biology · 2024-07-02 · 25 citations

  articleOpen accessCorresponding

  The vegetative insecticidal protein Vip3Aa from Bacillus thuringiensis (Bt) has been produced by transgenic crops to counter pest resistance to the widely used crystalline (Cry) insecticidal proteins from Bt. To proactively manage pest resistance, there is an urgent need to better understand the genetic basis of resistance to Vip3Aa, which has been largely unknown. We discovered that retrotransposon-mediated alternative splicing of a midgut-specific chitin synthase gene was associated with 5,560-fold resistance to Vip3Aa in a laboratory-selected strain of the fall armyworm, a globally important crop pest. The same mutation in this gene was also detected in a field population. Knockout of this gene via CRISPR/Cas9 caused high levels of resistance to Vip3Aa in fall armyworm and 2 other lepidopteran pests. The insights provided by these results could help to advance monitoring and management of pest resistance to Vip3Aa.

  PublisherOA PDFDOI

• Mismatch between lab-generated and field-evolved resistance to transgenic Bt crops in<i>Helicoverpa zea</i>

  Proceedings of the National Academy of Sciences · 2024-11-06 · 24 citations

  articleOpen accessSenior authorCorresponding

  Transgenic crops producing crystalline (Cry) proteins from the bacterium Bacillus thuringiensis (Bt) have been used extensively to control some major crop pests. However, many populations of the noctuid moth Helicoverpa zea , one of the most important crop pests in the United States, have evolved practical resistance to several Cry proteins including Cry1Ac. Although mutations in single genes that confer resistance to Cry proteins have been identified in lab-selected and gene-edited strains of H. zea and other lepidopteran pests, the genetic basis of field-evolved resistance to Cry proteins in H. zea has remained elusive. We used a genomic approach to analyze the genetic basis of field-evolved resistance to Cry1Ac in 937 H. zea derived from 17 sites in seven states of the southern United States. We found evidence for extensive gene flow among all populations studied. Field-evolved resistance was not associated with mutations in 20 single candidate genes previously implicated in resistance or susceptibility to Cry proteins in H. zea or other lepidopterans. Instead, resistance in field samples was associated with increased copy number of a cluster of nine trypsin genes. However, trypsin gene amplification occurred in a susceptible sample and not in all resistant samples, implying that this amplification does not always confer resistance and mutations in other genes also contribute to field-evolved resistance to Cry1Ac in H. zea . The mismatch between lab-generated and field-evolved resistance in H. zea is unlike other cases of Bt resistance and reflects challenges for managing this pest.

  PublisherOA PDFDOI

Frequent coauthors

• Yves Carrière

  University of Arizona

  157 shared

• Timothy J. Dennehy

  Arizona State University

  84 shared

• David G. Heckel

  Max Planck Institute for Chemical Ecology

  70 shared

• Jeffrey A. Fabrick

  U.S. Arid Land Agricultural Research Center

  59 shared

• Yong-Biao Liu

  University of Arizona

  54 shared

• Marshall W. Johnson

  University of Florida

  44 shared

• Luke Masson

  National Research Council Canada

  43 shared

• Christa Ellers‐Kirk

  BASF (United States)

  43 shared

Labs

• Department of EntomologyPI