Research Project: Sustainable Pest Management for Arid-Land Agroecosystems

Location: Pest Management and Biocontrol Research

2023 Annual Report

Accomplishments
1. Increase in global resistance to genetically engineered Bacillus thuringiensis (Bt) crops. Transgenic plants producing insecticidal proteins from Bacillus thuringiensis (Bt) are grown widely to control pests, but evolution of insect resistance has reduced the efficacy of Bt crops. An ARS scientist at Maricopa, Arizona, and collaborators at the University of Arizona, analyzed global resistance monitoring data for the first 25 years of cultivation of Bt crops including corn, cotton, soybean, and sugarcane. A total of 73 cases were examined including 24 pest species from 12 countries with cases of practical resistance arising from three in 2005 to 26 in 2020. Practical resistance was documented in some populations of 11 pest species, collectively affecting nine widely used crystalline (Cry) Bt toxins in seven countries. Conversely, 30 cases reflect no decrease in susceptibility to Bt crops in populations of 15 pest species in nine countries. The remaining 17 cases provide early warnings of resistance, which entail genetically-based decreases in susceptibility without evidence of reduced efficacy. Numerous factors that can lead to sustained susceptibility to Bt crops were reviewed, providing improvements for the sustainability of current and future transgenic insecticidal crops.

2. CRISPR/Cas9 gene editing feasible in Lygus. CRISPR/Cas9-mediated gene editing is the foremost tool available for functional genomics approaches and targeted genomic engineering applications; however, the technique is species-specific and often requires significant optimization, especially in non-model organisms such as Lygus hesperus. The applicability of the CRISPR/Cas9 system for this species was successfully demonstrated by a team of ARS researchers in Maricopa, Arizona. Eggs injected with the Cas9 enzyme and sgRNAs targeting either cardinal or cinnabar, two eye pigmentation genes, developed red eyes instead of brown eyes typical of wildtypes. Although atypical coloration in both experimental groups largely persisted throughout the nymphal stages, adult manifestation of the phenotype was limited to the cinnabar group, and atypical eye coloration was associated with disruptions in the sequence of the respective target genes. The heritability and persistence of the red eye phenotype across multiple generations demonstrated that clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing can be applied to L. hesperus and that eye pigmentation genes are useful for tracking genetic manipulation.

3. Gene editing identifies a key receptor gene of pest resistance to transgenic Bacillus thuringiensis (Bt) crops. The corn earworm, Helicoverpa zea, is a major New World pest of many crops that has evolved resistance to transgenic corn and cotton producing different Bt protein toxins. Understanding of the genetic basis of such resistance is needed to better monitor, manage, and counter pest resistance to Bt crops. An ARS researcher in Maricopa, Arizona, and collaborators at the University of Arizona, showed that mutations introduced by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing in the corn earworm gene encoding an ATP-binding cassette protein (HzABCA2) causes resistance to the Cry2Ab Bt toxin. Disruptive mutations in HzABCA2 facilitated the creation of two Cry2Ab-resistant strains in which all resistant individuals tested had disruptive mutations in HzABCA2. The results demonstrate that HzABCA2 mutations can cause high levels of resistance to Cry2Ab, and that this gene is a leading candidate for monitoring corn earworm for Cry2Ab resistance in the field.

4. Complex molecular basis of lab- and field-selected pink bollworm resistance to transgenic Bacillus thuringiensis (Bt) cotton. Cotton has been genetically engineered to produce insect-killing proteins from the bacterium Bacillus thuringiensis (Bt) to control major pests that include the pink bollworm, one of the most damaging pests of cotton world-wide. Genetically engineered Bt crops have many advantages, including enhanced pest suppression, improved yields, increased farmer profits, and decreased use of conventional insecticides thereby benefiting the environment and human health; however, these benefits are reduced when pests evolve resistance to Bt crops. The pink bollworm rapidly evolved resistance to Bt cotton in India, but not in China or the United States where this invasive pest was eradicated using Bt cotton, sterile moth releases, and other tactics. An ARS researcher from Maricopa, Arizona, and collaborators from the University of Arizona, compared the genetic profiles of Bt-resistant pink bollworm taken from lab-selected strains from the United States and China and field-selected populations from India. Testing showed the genetic basis of resistance was similar across countries and between resistance selected in the lab versus the field suggesting that lab selection can be useful for identifying genes likely to be important in field-evolved resistance to Bt crops. Likely, differences in management practices among countries caused the different outcomes.

5. Development of a method to track insect dispersal. Tracking dispersal patterns in agroecosystems is essential for efficiently managing arthropod pests and conserving natural enemies and pollinators. An ARS researcher at Maricopa, Arizona, developed and refined a method to tag key cotton pests (lygus and whitefly), natural enemies, and pollinators with a fluorophore that glows brightly under ultraviolet light. The key features of this novel marking procedure are that it is inexpensive, persistent, easily detected, does not affect insect behavior, and works equally well on large and small insects (e.g., whiteflies and parasitoids). The novel fluorophore marking method will expedite future dispersal research on whiteflies and various other pest and beneficial arthropod species.

6. Monitoring lygus bug and natural enemy movement in trap-cropped strawberry fields. The lygus bug is the major strawberry pest, but prefer to feed on alfalfa and many types of native weeds. As such, intercropping strips of alfalfa (trap cropping) within strawberry production fields and allowing weeds to flower adjacent to the fields can serve as a sink for both lygus and its natural enemies. An ARS scientist at Maricopa, Arizona, teamed up with University of California scientists to study the population dynamics and dispersal characteristics of lygus and its associated predator complex in organically grown strawberry fields embedded with strips of alfalfa and surrounded by weedy vegetation. The research showed that the lygus population was up to 2.5 times higher in alfalfa and that most marked lygus and predators that emigrated from senescing weeds were recovered from alfalfa rather than strawberry. Moreover, the marked predator-to-lygus ratio found in alfalfa compared to strawberries was 5:1. Trap cropping effectively reduced the infestation of lygus in strawberries demonstrating that converting weedy areas to native perennial plantings could mitigate the risk of pest migration while conserving beneficial insects.

Review Publications
Hull, J.J., Brent, C.S., Fu, T., Wang, G., Christie, A.E. 2022. Mining Lygus hesperus (western tarnished plant bug) transcriptomic data for transient receptor potential channels: Expression profiling and functional characterization of a painless homolog. Comparative Biochemistry and Physiology. 44. Article 101027. https://doi.org/10.1016/j.cbd.2022.101027.
Guo, H., Liu, X., Long, G., Gong, L., Zhang, M., Ma, Y., Hull, J.J., Dewer, Y., He, M., He, P. 2022. Functional characterization of developmentally critical genes in the white-backed planthopper: Efficacy of nanoparticle-based dsRNA sprays for pest control. Pest Management Science. 79(3):1048-1061. https://doi.org/10.1002/ps.7271.
Fabrick, J.A., Heu, C.C., LeRoy, D.M., DeGain, B.A., Yelich, A.J., Unnithan, G.C., Wu, Y., Li, X., Carriere, Y., Tabashnik, B.E. 2022. Knockout of ABC transporter gene ABCA2 confers resistance to Bt toxin Cry2Ab in Helicoverpa zea. Scientific Reports. 12. Article 16706. https://doi.org/10.1038/s41598-022-21061-2.
Tabashnik, B.E., Fabrick, J.A., Carriere, Y. 2023. Global patterns of insect resistance to transgenic Bt crops: The first 25 years. Journal of Economic Entomology. 116(2):297-309. https://doi.org/10.1093/jee/toac183.
Stahlke, A.R., Chang, J., Chudalayandi, S., Heu, C.C., Geib, S.M., Scheffler, B.E., Childers, A.K., Fabrick, J.A. 2023. Chromosome-scale genome assembly of the pink bollworm, Pectinophora gossypiella, a global pest of cotton. G3, Genes/Genomes/Genetics. 13(4). Article jkad040. https://doi.org/10.1093/g3journal/jkad040.
Fabrick, J.A., Li, X., Carriere, Y., Tabashnik, B. 2023. Molecular genetic basis of lab- and field-selected Bt resistance in pink bollworm. Insects. 14(2). Article 201. https://doi.org/10.3390/insects14020201.
Guo, H., Long, G., Liu, X., Ma, Y., Zhang, M., Gong, L., Dewer, Y., Hull, J.J., Wang, M., Wang, Q., He, M., He, P. 2023. Functional characterization of tyrosine melanin genes in the white-backed planthopper and utilization of a spray-based nanoparticle-wrapped dsRNA technique for pest control. International Journal of Biological Macromolecules. 230. Article 123123. https://doi.org/10.1016/j.ijbiomac.2022.123123.
Tabashnik, B.E., Carriere, Y., Wu, Y., Fabrick, J.A. 2023. Global perspectives on field-evolved resistance to transgenic Bt crops: A special collection. Journal of Economic Entomology. 116(2):269-274. https://doi.org/10.1093/jee/toad054.
Wang, M., Wang, J., Yasen, A., Fan, B., Hull, J.J., Shen, X. 2023. Determination of key components in the Bombyx mori p53 apoptosis regulation network using Y2H-Seq. Insects. 14(4). Article 362. https://doi.org/10.3390/insects14040362.
Weaver, M.A., Callicott, K.A., Mehl, H.L., Opoku, J., Park, L.C., Fields, K., Mandel, J.R. 2022. Characterization of the Aspergillus flavus population from highly aflatoxin-contaminated corn in the United States. Toxins. 14(11). Article 755. https://doi.org/10.3390/toxins14110755.
Ma, Y., Gong, L., Zhang, M., Liu, X., Guo, H., Hull, J.J., Long, G., Wang, H., Dewer, Y., Zhang, F., He, M., He, P. 2023. Two antennae-enriched carboxylesterases mediate olfactory responses and degradation of ester volatiles in the German cockroach Blattella germanica. Journal of Agricultural and Food Chemistry. 71(12):4789-4801. https://doi.org/10.1021/acs.jafc.2c08488.
Teng, H., Zuo, Y., Yuan, J., Fabrick, J.A., Wu, Y., Yang, Y. 2022. High frequency of ryanodine receptor and cytochrome P450 CYP9A186 mutations in insecticide-resistant field populations of Spodoptera exigua from China. Pesticide Biochemistry and Physiology. 186. Article 105153. https://doi.org/10.1016/j.pestbp.2022.105153.
Tabashnik, B.E., Unnithan, G.C., Yelich, A., Fabrick, J.A., Dennehy, T.J., Carriere, Y. 2022. Responses to Bt toxin Vip3Aa by pink bollworm larvae resistant or susceptible to Cry toxins. Pest Management Science. 78(10):3973-3979. https://doi.org/10.1002/ps.7016.
Bordini, I., Naranjo, S.E., Fournier, A., Ellsworth, P. 2023. Spatial scale of non-target effects of cotton insecticides. PLOS ONE. 18(5). Article e0272831. https://doi.org/10.1371/journal.pone.0272831.
Naranjo, S.E., Canas, L., Ellsworth, P.C. 2022. Mortality dynamics of a polyphagous invasive herbivore reveal clues in its agroecosystem success. Pest Management Science. 78(10):3988-4055. https://doi.org/10.1002/ps.7018.
Liu, X., Long, G., Guo, H., Ma, Y., Gong, L., Zhang, M., Hull, J.J., Dewer, Y., Liu, L., He, M., He, P. 2023. Functional characterization of five developmental signaling network genes in the white-backed planthopper: Potential application for pest management. Pest Management Science. 79(8):2869-2881. https://doi.org/10.1002/ps.7464.