l e t t e r sHow an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants 1 , but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood 2 . We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.The global pest P. xylostella (Lepidoptera: Yponomeutidae) is thought to have coevolved with the crucifer plant family 3 ( Supplementary Fig. 1) and has become the most destructive pest of economically important food crops, including rapeseed, cauliflower and cabbage 4 . Recently, the total cost of damage and management worldwide was estimated at $4-5 billion per annum 5,6 . This insect is the first species to have evolved resistance to dichlorodiphenyltrichloroethane (DDT) in the 1950s 7 and to Bacillus thuringiensis (Bt) toxins in the 1990s 8 and has developed resistance to all classes of insecticide, making it increasingly difficult to control 9,10 . P. xylostella provides an exceptional system for understanding the genetic and molecular bases of how insect herbivores cope with the broad range of plant defenses and chemicals encountered in the environment (Supplementary Fig. 2).We used a P. xylostella strain (Fuzhou-S) collected from a field in Fuzhou in southeastern China (26.08 °N, 119.28 °E) for sequencing ( Supplementary Fig. 1). Whole-genome shotgun-based Illumina sequencing of single individuals (Supplementary Table 1), even after ten generations of laboratory inbreeding, resulted in a poor initial assembly (N50 = 2.4 kb, representing the size above which 50% of the total length of the sequences is included), owing to high levels of heterozygosity ( Supplementary Figs. 3 and 4 and Supplementary Table 2). Subsequently, we sequenced 100,800 fosmid clones (comprising ~10× the genome length) to a depth of 200× ( Supplementary Fig. 5 and Supplementary Tables 3-5), assembling the resulting sequence data into 1,819 scaffolds, with an N50 of 737 kb, spanning ~394 Mb of the genome sequence (version 1; Supplementary Fig. 6 and Supplementary Table 6). The assembly covered 85.5% of a set of protein-coding ESTs (Supplementary Tables 7 and 8) generated by transcriptome sequencing 11 . Alignment of a subject scaffold against a 126-kb BAC (GenBank GU058050) from an altern...

The diamondback moth, Plutella xylostella is a cosmopolitan pest that has evolved resistance to all classes of insecticide, and costs the world economy an estimated US $4-5 billion annually. We analyse patterns of variation among 532 P. xylostella genomes, representing a worldwide sample of 114 populations. We find evidence that suggests South America is the geographical area of origin of this species, challenging earlier hypotheses of an Old-World origin. Our analysis indicates that Plutella xylostella has experienced three major expansions across the world, mainly facilitated by European colonization and global trade. We identify genomic signatures of selection in genes related to metabolic and signaling pathways that could be evidence of environmental adaptation. This evolutionary history of P. xylostella provides insights into transoceanic movements that have enabled it to become a worldwide pest.

The experimental demonstration of a broad-area Quasi-continuous-wave (QCW) laser-diode array pumped cesium vapor laser is reported in this letter according to our experimental results. We used a volume-Bragg grating to narrow the spectral linewidth for acquirement of enough resonance transitions. A glass cylindrical cell filled with cesium/buffer gas was set in an end-pumped flat-concave cavity and the gas pressure was set lower than 1atm. Using the QCW drive mode with the repetitive rate and pulse width of 1kHz and 50μs, respectively, 13.45μJ pulse energy has been achieved with the slope efficiency of about ∼1.8%.

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bandwidth of a high-power laser-diode array was effectively suppressed by use of an off-axis external-cavity technique. The external cavity consisted of a beam-transformation system and a pair of off-axis volume Bragg gratings. During operation at a drive current of 40 A, we reduced the bandwidth's full width at half-maximum from 3.3 to 0.24 nm (14-fold reduction) and achieved an output power of 20 W, or as much as 87% of the power radiated by a free-running laser-diode array without an external cavity.

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