The speciose insect order Lepidoptera (moths and butterflies) and their closest relatives, Trichoptera (caddis flies), share a female-heterogametic sex chromosome system. Originally a Z/ZZ (female/male) system, it evolved by chromosome rearrangement to a WZ/ZZ (female/male) system in the most species-rich branch of Lepidoptera, a monophyletic group consisting of Ditrysia and Tischeriina, which together comprise more than 98% of all species. Further sporadic rearrangements created multi-sex chromosome systems; sporadic losses of the W changed the system formally back to Z/ZZ in some species. Primary sex determination depends on a Z-counting mechanism in Z/ZZ species, but on a female-determining gene, Fem, in the W chromosome of the silkworm. The molecular mechanism is unknown in both cases. The silkworm shares the last step, dsx, of the hierarchical sex-determining pathway with Drosophila and other insects investigated, but probably not the intermediate steps between the primary signal and dsx. The W chromosome is heterochromatic in most species. It contains few genes and is flooded with interspersed repetitive elements. In interphase nuclei of females it is readily discernible as a heterochromatic body which grows with increasing degree of polyploidy in somatic cells. It is used as a marker for the genetic sex in studies of intersexes and Wolbachia infections. The sex chromosome system is being exploited in economically important species. Special strains have been devised for mass rearing of male-only broods in the silkworm for higher silk production and in pest species for the release of sterile males in pest management programs.

Manduca sexta, known as the tobacco hornworm or Carolina sphinx moth, is a lepidopteran insect that is used extensively as a model system for research in insect biochemistry, physiology, neurobiology, development, and immunity. One important benefit of this species as an experimental model is its extremely large size, reaching more than 10 g in the larval stage. M. sexta larvae feed on solanaceous plants and thus must tolerate a substantial challenge from plant allelochemicals, including nicotine. We report the sequence and annotation of the M. sexta genome, and a survey of gene expression in various tissues and developmental stages. The Msex_1.0 genome assembly resulted in a total genome size of 419.4 Mbp. Repetitive sequences accounted for 25.8% of the assembled genome. The official gene set is comprised of 15,451 protein-coding genes, of which 2498 were manually curated. Extensive RNA-seq data from many tissues and developmental stages were used to improve gene models and for insights into gene expression patterns. Genome wide synteny analysis indicated a high level of macrosynteny in the Lepidoptera. Annotation and analyses were carried out for gene families involved in a wide spectrum of biological processes, including apoptosis, vacuole sorting, growth and development, structures of exoskeleton, egg shells, and muscle, vision, chemosensation, ion channels, signal transduction, neuropeptide signaling, neurotransmitter synthesis and transport, nicotine tolerance, lipid metabolism, and immunity. This genome sequence, annotation, and analysis provide an important new resource from a well-studied model insect species and will facilitate further biochemical and mechanistic experimental studies of many biological systems in insects.

In the adzuki bean borer, Ostrinia scapulalis, the sex ratio in most progenies is 1 : 1. Females from Wolbachia-infected matrilines, however, give rise to all-female broods when infected and to all-male broods when cured of the infection. These observations had been interpreted as Wolbachia-induced feminization of genetic males into functional females. Here, we show that the interpretation is incorrect. Females from both lines have a female karyotype with a WZ sex-chromosome constitution while males are ZZ. At the time of hatching from eggs, WZ and ZZ individuals are present at a 1 : 1 ratio in broods from uninfected, infected and cured females. In broods from Wolbachia-infected females, ZZ individuals die during larval development, whereas in those from cured females, WZ individuals die. Hence, development of ZZ individuals is impaired by Wolbachia but development of WZ females may require the presence of Wolbachia in infected matrilines. Sexual mosaics generated (i) by transfection of uninfected eggs and (ii) by tetracycline treatment of Wolbachia-infected mothers prior to oviposition were ZZ in all tissues, including typically female organs. We conclude that: (i) Wolbachia acts by manipulating the sex determination of its host; and (ii) although sexual mosaics can survive, development of a normal female is incompatible with a ZZ genotype.

The (TTAGG)n sequence is supposed to be an ancestral DNA motif of telomeres in insects. Here we examined the occurrence of TTAGG telomeric repeats in other arthropods and their close relatives by Southern hybridization of genomic DNAs and fluorescence in-situ hybridization (FISH) of chromosomes with (TTAGG)n probes or, alternatively, with the 'vertebrate' telomeric probe, (TTAGGG)n. Our results show that the (TTAGG)n motif is conserved in entognathous hexapods (Diplura and Collembola), crustaceans (Malacostraca, Branchiura, Pentastomida, and Branchiopoda), myriapods (Diplopoda and Chilopoda), pycnogonids, and most chelicerates (Palpigradi, Amblypygi, Acari, Opiliones, Scorpiones, Pseudoscorpiones, and Solifugae) but not in spiders (Araneae). The presence of TTAGG repeats in these groups suggests that the sequence is an ancestral motif of telomeres not only in insects but in Arthropoda. We failed, however, to detect the TTAGG repeats in close relatives of the arthropods, Tardigrada and Onychophora. But while Onychophora had the 'vertebrate' (TTAGGG)n motif instead, the Tardigrada did not. The (TTAGG)n motif probably evolved from the (TTAGGG)n motif. Based on our and compiled data, we presume that the 'vertebrate' motif (TTAGGG)n is an ancestral motif of telomeres in bilaterian animals and possibly also in the superclade including animals, fungi and amoebozoans.

Lepidoptera, i.e. moths and butterflies, have a female heterogametic sex chromosome system, with most females having a WZ constitution while males are ZZ. Besides this predominant WZ/ZZ