An official website of the United States government
The evolution of pest resistance to management tools reduces productivity and results in economic losses in agricultural systems. To slow its emergence and spread, monitoring and prevention practices are implemented in resistance management programs. Recent work suggests that genomic approaches can identify signs of emerging resistance to aid in resistance management. Here, we empirically examined the sensitivity of genomic monitoring for resistance management in transgenic Bt crops, a globally important agricultural innovation. Whole genome resequencing of wild North AmericanHelicoverpa zeacollected from non-expressing refuge and plants expressing Cry1Ab confirmed that resistance-associated signatures of selection were detectable after a single generation of exposure. Upon demonstrating its sensitivity, we applied genomic monitoring to wildH. zeathat survived Vip3A exposure resulting from cross-pollination of refuge plants in seed-blended plots. Refuge seed interplanted with transgenic seed exposedH. zeato sublethal doses of Vip3A protein in corn ears and was associated with allele frequency divergence across the genome. Some of the greatest allele frequency divergence occurred in genomic regions adjacent to a previously described candidate gene for Vip3A resistance. Our work highlights the power of genomic monitoring to sensitively detect heritable changes associated with field exposure to Bt toxins and suggests that seed-blended refuge will likely hasten the evolution of resistance to Vip3A in lepidopteran pests.
more »
« less
This content will become publicly available on November 19, 2025
Mismatch between lab-generated and field-evolved resistance to transgenic Bt crops in Helicoverpa zea
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 inH. zeais unlike other cases of Bt resistance and reflects challenges for managing this pest.
more »
« less
- PAR ID:
- 10563439
- Publisher / Repository:
- PNAS
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 121
- Issue:
- 47
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The fall armyworm ( Spodoptera frugiperda ) is a highly polyphagous lepidopteran pest of relevant food and fiber staple crops. In the Americas, transgenic corn and cotton producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have controlled and reduced the damage caused by S. frugiperda . However, cases of field-evolved S. frugiperda resistance to Bt corn producing the Cry1F insecticidal protein have been documented in North and South America. When characterized, field resistance to Cry1F is linked to insertions and mutations resulting in a modified or truncated ABC transporter subfamily C2 ( SfABCC2 ) protein that serves as Cry1F receptor in susceptible S. frugiperda . In this work, we present detection of a large genomic deletion (~ 8 kb) affecting the SfABCC2 and an ABC transporter gene subfamily 3 –like gene ( SfABCC3 ) as linked to resistance to Cry1F corn in a S . frugiperda strain from Florida (FL39). Monitoring for this genomic deletion using a discriminatory PCR reaction in field-collected S. frugiperda moths detected individuals carrying this allele in Florida, but not in surrounding states. This is the first report of a large genomic deletion being involved in resistance to a Bt insecticidal protein.more » « less
-
Fall armyworm is one of the main pests of conventional and Bacillus thuringiensis (Bt) corn in many countries in the Americas, Africa, Asia and in Australia. We conducted diet-overlay bioassays to determine the status of susceptibility to four Bt proteins (Cry1A.105, Cry2Ab2, Cry1F and Cry1Ac) in three different populations of fall armyworm from Mexico, and one population from Puerto Rico. Bioassays showed that fall armyworms from Puerto Rico were resistant to Cry1F with a resistance ratio 50 (RR50) higher than 10,000 ng/cm2 and to Cry1Ac with a RR50 = 12.2 ng/cm2, displaying the highest median lethal concentration (LC50) values to all Bt proteins tested. The effective concentration 50 (EC50) values further confirmed the loss of susceptibility to Cry1F and Cry1Ac in this population. However, LC50 and EC50 results with Cry1A.105 and Cry2Ab2 revealed that fall armyworm from Puerto Rico remained largely susceptible to these two proteins. The Mexican populations were highly susceptible to all the Bt proteins tested and displayed the lowest LC50 and EC50 values to all Bt proteins. Our results suggest that Cry1F and Cry1Ac resistance is stable in fall armyworm from Puerto Rico. However, this population remains susceptible to Cry1A.105 and Cry2Ab2. Results with Mexican fall armyworms suggest that possible deployment of Bt corn in Mexico will not be immediately challenged by Bt-resistant genes in those regions.more » « less
-
Abstract The European corn borer (Ostrinia nubilalis) is an agricultural pest and burgeoning model for research on speciation, seasonal adaptation and insect resistance management. Although previous work inO. nubilalishas identified genes associated with differences in life cycle, reproduction, and resistance toBttoxins, the general lack of a robust gene‐editing protocol forO. nubilalishas been a barrier to functional validation of candidate genes. Here, we demonstrate an efficient and practical methodology for heritable gene mutagenesis inO. nubilalisusing the CRISPR/Cas9 genome editing system. Precise loss‐of‐function (LOF) mutations were generated at two circadian clock genes,period(per) andpigment‐dispersing factor receptor(pdfr), and a developmental gene,prothoracicotropic hormone(ptth). Precluding the need for a visible genetic marker, gene‐editing efficiency remained high across different single guide RNAs (sgRNA) and germline transmission of mutations to F1offspring approached 100%. When single or dual sgRNAs were injected at a high concentration, gene‐specific phenotypic differences in behaviour and development were identified in F0mutants. Specifically, F0gene mutants demonstrated that PER, but not PDFR, is essential for normal timing of eclosion. PTTH F0mutants were significantly heavier and exhibited a higher incidence of diapause. This work will accelerate future studies of gene function inO. nubilalisand facilitate the development of similar screens in other Lepidopteran and non‐model insects.more » « less
-
Abstract During the last decade, the sorghum aphid (Melanaphis sorghi), previously identified as sugarcane aphid (Melanaphis sacchari), became a serious pest of sorghum, spreading to all sorghum‐producing regions in the United States, Mexico, and South America, where crop losses of 50%–100% have been reported. Developing sorghum cultivars with resistance to this insect is the most sustainable strategy for long‐term pest management. To design cultivars with aphid resistance, comprehensively understanding the mechanisms underlying aphid survival, host plant resistance, and aphid–sorghum interactions is critical. In this review, we summarize the comprehensive efforts to characterize the aphid populations as well as their interaction with sorghum plants via hormonal pathways that trigger various genes including leucine rich repeats, WRKY transcription factors, lipoxygenases, calmodulins, and others. We discuss efforts made during the last decade to identify specific genomic regions and candidate genes that confer aphid resistance, as well as describe recent successes and potential challenges in breeding for aphid resistance. Furthermore, we discuss the use of disruptive technologies like high‐throughput phenotyping, artificial intelligence, or machine learning for developing aphid resistant sorghum cultivars. Integration of these new technologies has the potential to accelerate the development and design of novel traits that confer durable aphid resistance in new sorghum cultivars to defend sorghum against new aphid genotype development.more » « less
