Background The western flower thrips, Frankliniella occidentalis (Pergande), is a globally invasive pest and plant virus vector on a wide array of food, fiber, and ornamental crops. The underlying genetic mechanisms of the processes governing thrips pest and vector biology, feeding behaviors, ecology, and insecticide resistance are largely unknown. To address this gap, we present the F. occidentalis draft genome assembly and official gene set. Results We report on the first genome sequence for any member of the insect order Thysanoptera. Benchmarking Universal Single-Copy Ortholog (BUSCO) assessments of the genome assembly (size = 415.8 Mb, scaffold N50 = 948.9 kb) revealed a relatively complete and well-annotated assembly in comparison to other insect genomes. The genome is unusually GC-rich (50%) compared to other insect genomes to date. The official gene set (OGS v1.0) contains 16,859 genes, of which ~ 10% were manually verified and corrected by our consortium. We focused on manual annotation, phylogenetic, and expression evidence analyses for gene sets centered on primary themes in the life histories and activities of plant-colonizing insects. Highlights include the following: (1) divergent clades and large expansions in genes associated with environmental sensing (chemosensory receptors) and detoxification (CYP4, CYP6, and CCE enzymes) of substances encountered in agricultural environments; (2) a comprehensive set of salivary gland genes supported by enriched expression; (3) apparent absence of members of the IMD innate immune defense pathway; and (4) developmental- and sex-specific expression analyses of genes associated with progression from larvae to adulthood through neometaboly, a distinct form of maturation differing from either incomplete or complete metamorphosis in the Insecta. Conclusions Analysis of the F. occidentalis genome offers insights into the polyphagous behavior of this insect pest that finds, colonizes, and survives on a widely diverse array of plants. The genomic resources presented here enable a more complete analysis of insect evolution and biology, providing a missing taxon for contemporary insect genomics-based analyses. Our study also offers a genomic benchmark for molecular and evolutionary investigations of other Thysanoptera species.

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Vector-borne viruses are a threat to human, animal, and plant health worldwide, requiring the development of novel strategies for their control. Tomato spotted wilt virus (TSWV) is one of the 10 most economically significant plant viruses and, together with other tospoviruses, is a threat to global food security. TSWV is transmitted by thrips, including the western flower thrips, Frankliniella occidentalis. Previously, we demonstrated that the TSWV glycoprotein GN binds to thrips vector midguts. We report here the development of transgenic plants that interfere with TSWV acquisition and transmission by the insect vector. Tomato plants expressing GN-S protein supported virus accumulation and symptom expression comparable with nontransgenic plants. However, virus titers in larval insects exposed to the infected transgenic plants were three-log lower than insects exposed to infected nontransgenic control plants. The negative effect of the GN-S transgenics on insect virus titers persisted to adulthood, as shown by four-log lower virus titers in adults and an average reduction of 87% in transmission efficiencies. These results demonstrate that an initial reduction in virus infection of the insect can result in a significant decrease in virus titer and transmission over the lifespan of the vector, supportive of a dose-dependent relationship in the virus-vector interaction. These findings demonstrate that plant expression of a viral protein can be an effective way to block virus transmission by insect vectors.

54Background: The western flower thrips, Frankliniella occidentalis (Pergande), is a globally 55 invasive pest and plant virus vector on a wide array of food, fiber and ornamental crops. While 56 there are numerous studies centered on thrips pest and vector biology, feeding behaviors, ecology, 57 and insecticide resistance, the underlying genetic mechanisms of the processes governing these 58 areas of research are largely unknown. To address this gap, we present the F. occidentalis draft 59 genome assembly and official gene set. 60Results: We report on the first genome sequence for any member of the insect order Thysanoptera. 61 Benchmarking Universal Single-Copy Ortholog (BUSCO) assessments of the genome assembly 62 (size = 415.8 Mb, scaffold N50 = 948.9 Kb) revealed a relatively complete and well-annotated 63 assembly in comparison to other insect genomes. The genome is unusually GC-rich (50%) 64 compared to other insect genomes to date. The official gene set (OGS v1.0) contains 16,859 genes, 65 of which ~10% were manually verified and corrected by our consortium. We focused on manual 66 annotation, phylogenetic and expression evidence analyses for gene sets centered on primary 67 themes in the life histories and activities of plant-colonizing insects. Highlights include: 1) 68 divergent clades and large expansions in genes associated with environmental sensing 69 (chemosensory receptors) and detoxification (CYP4, CYP6 and CCE enzymes) of substances 70 encountered in agricultural environments; 2) a comprehensive set of salivary gland-associated 71 genes supported by enriched expression; 3) apparent absence of members of the IMD innate 72 3 immune defense pathway; and 4) developmental-and sex-specific expression analyses of genes 73 associated with progression from larvae to adulthood through neometaboly, a distinct form of 74 maturation compared to complete metamorphosis in the Holometabola. 75 Conclusions: Analysis of the F. occidentalis genome offers insights into the polyphagous behavior 76 of this insect pest to find, colonize and survive on a widely diverse array of plants. The genomic 77 resources presented here enable a more complete analysis of insect evolution and biology, 78 providing a missing taxon for contemporary insect genomics-based analyses. Our study also offers 79 a genomic benchmark for molecular and evolutionary investigations of other thysanopteran 80 species. 81 KEY WORDS 82 Thysanoptera, western flower thrips, hemipteroid assemblage, insect genomics, tospovirus, 83 virus-vector interactions, salivary glands, chemosensory receptors, opsins, detoxification, innate 84 immunity 85 86 BACKGROUND 87Thrips are small, polyphagous and cosmopolitan insects that comprise the order Thysanoptera. 88Thysanoptera lies within the Paraneoptera, also commonly called the "hemipteroid assemblage" 89 which also includes the orders Hemiptera, Psocoptera, and Phthiraptera. Among the over 7,000 90 reported thrips species classified into nine families with an additional five identified from fossil 91 species [1]...

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