The cabbage looper, Trichoplusia ni, is a globally distributed highly polyphagous herbivore and an important agricultural pest. T. ni has evolved resistance to various chemical insecticides, and is one of the only two insect species that have evolved resistance to the biopesticide Bacillus thuringiensis (Bt) in agricultural systems and has been selected for resistance to baculovirus infections. We report a 333‐Mb high‐quality T. ni genome assembly, which has N50 lengths of scaffolds and contigs of 4.6 Mb and 140 Kb, respectively, and contains 14,384 protein‐coding genes. High‐density genetic maps were constructed to anchor 305 Mb (91.7%) of the assembly to 31 chromosomes. Comparative genomic analysis of T. ni with Bombyx mori showed enrichment of tandemly duplicated genes in T. ni in families involved in detoxification and digestion, consistent with the broad host range of T. ni. High levels of genome synteny were found between T. ni and other sequenced lepidopterans. However, genome synteny analysis of T. ni and the T. ni derived cell line High Five (Hi5) indicated extensive genome rearrangements in the cell line. These results provided the first genomic evidence revealing the high instability of chromosomes in lepidopteran cell lines known from karyotypic observations. The high‐quality T. ni genome sequence provides a valuable resource for research in a broad range of areas including fundamental insect biology, insect‐plant interactions and co‐evolution, mechanisms and evolution of insect resistance to chemical and biological pesticides, and technology development for insect pest management.

bTwo populations of Trichoplusia ni that had developed resistance to Bacillus thuringiensis sprays (Bt sprays) in commercial greenhouse vegetable production were tested for resistance to Bt cotton (BollGard II) plants expressing pyramided Cry1Ac and Cry2Ab. The T. ni colonies resistant to Bacillus thuringiensis serovar kurstaki formulations were not only resistant to the Bt toxin Cry1Ac, as previously reported, but also had a high frequency of Cry2Ab-resistant alleles, exhibiting ca. 20% survival on BollGard II foliage. BollGard II-resistant T. ni strains were established by selection with BollGard II foliage to further remove Cry2Ab-sensitive alleles in the T. ni populations. The BollGard II-resistant strains showed incomplete resistance to BollGard II, with adjusted survival values of 0.50 to 0.78 after 7 days. The resistance to the dual-toxin cotton plants was conferred by two genetically independent resistance mechanisms: one to Cry1Ac and one to Cry2Ab. The 50% lethal concentration of Cry2Ab for the resistant strain was at least 1,467-fold that for the susceptible T. ni strain. The resistance to Cry2Ab in resistant T. ni was an autosomally inherited, incompletely recessive monogenic trait. Results from this study indicate that insect populations under selection by Bt sprays in agriculture can be resistant to multiple Bt toxins and may potentially confer resistance to multitoxin Bt crops. Evolution of pesticide resistance in insect populations is a continuing threat to the efficacy of both synthetic and biological insecticides. Resistance of insects to the biological insecticide Bacillus thuringiensis (Bt), a naturally occurring soil bacterium, was first reported in the 1980s for a pest of stored grains, Plodia interpunctella (1). Resistance to Bt in Plutella xylostella and Trichoplusia ni has been identified following frequent applications of sprayable Bt formulations in agricultural situations (2-4). Since the mid-1990s, crops genetically engineered to contain insecticidal toxins from Bt have increasingly been adopted worldwide (5). With the wide adoption of Bt crops, insect resistance is a serious threat to their continuing success. Field populations of several major pest species have been reported to have developed resistance after Bt crop adoption, leading to increased crop damage (6, 7). More insect species have been reported to have increased frequencies of resistant alleles in field populations after the adoption of Bt crops (8-11).Selective application of pesticides with different modes of action has been a principal strategy for insecticide resistance management. Similarly, Bt gene pyramiding, i.e., simultaneous expression of multiple toxins that have different binding sites in the target insects, is an effective strategy to delay the development of resistance to Bt crops. This has been promoted for Bt crops currently deployed in the United States and some other regions of the world (7, 12). Bt toxins Cry1Ac and Cry2Ab do not share the same binding sites in target Lepidoptera insects (13,14) and ha...

The resistance to the Bacillus thuringiensis (Bt) toxin Cry2Ab in a greenhouse-originated Trichoplusia ni strain resistant to both Bt toxins Cry1Ac and Cry2Ab was characterized. Biological assays determined that the Cry2Ab resistance in the T. ni strain was a monogenic recessive trait independent of Cry1Ac resistance, and there existed no significant cross-resistance between Cry1Ac and Cry2Ab in T. ni. From the dual-toxin-resistant T. ni strain, a strain resistant to Cry2Ab only was isolated, and the Cry2Ab resistance trait was introgressed into a susceptible laboratory strain to facilitate comparative analysis of the Cry2Ab resistance with the susceptible T. ni strain. Results from biochemical analysis showed no significant difference between the Cry2Ab-resistant and -susceptible T. ni larvae in midgut proteases, including caseinolytic proteolytic activity and zymogram profile and serine protease activities, in midgut aminopeptidase and alkaline phosphatase activity, and in midgut esterases and hemolymph plasma melanization activity. For analysis of genetic linkage of Cry2Ab resistance with potential Cry toxin receptor genes, molecular markers for the midgut cadherin, alkaline phosphatase (ALP), and aminopeptidase N (APN) genes were identified between the original greenhouse-derived dual-toxin-resistant and the susceptible laboratory T. ni strains. Genetic linkage analysis showed that the Cry2Ab resistance in T. ni was not genetically associated with the midgut genes coding for the cadherin, ALP, and 6 APNs (APN1 to APN6) nor associated with the ABC transporter gene ABCC2. Therefore, the Cry2Ab resistance in T. ni is conferred by a novel but unknown genetic mechanism.T he Gram-positive soil bacterium Bacillus thuringiensis (Bt) has been widely used as a microbial insecticide in sprayable formulations, and Bt toxins are the primary insecticidal proteins expressed in genetically engineered crops to confer insect resistance (1; ISAAA's GM Approval Database, http://www.isaaa.org /gmapprovaldatabase/). Since the mid-1990s, insect-resistant Bt crops have been rapidly adopted with proven economic and environmental benefits (2, 3). However, development of insect resistance to Bt toxins threatens the long-term success of application of Bt toxins for insect pest control. The genetic potential of insect populations to evolve Bt resistance has been well shown in laboratory selections, and cases of insect resistance to Bt formulations and Bt crops have occurred in insect populations under selection pressure by Bt sprays and Bt crops in the field (4-8).Studies of insect resistance to Bt toxins have so far been mostly on Lepidoptera pests to the toxin Cry1Ab or Cry1Ac (9-19), the two major Bt Cry toxins which are highly toxic to Lepidoptera pests and known to share the same binding sites in target insects (4, 20). Cry1Ab and Cry1Ac are the primary insecticidal proteins expressed in the current commercial transgenic Bt maize and Bt cotton varieties to target Lepidoptera pests in the field (21). Resistance to Cry1Ac and Cry1Ab ...

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