The tobacco cutworm, Spodoptera litura, is among the most widespread and destructive agricultural pests, feeding on over 100 crops throughout tropical and subtropical Asia. By genome sequencing, physical mapping and transcriptome analysis, we found that the gene families encoding receptors for bitter or toxic substances and detoxification enzymes, such as cytochrome P450, carboxylesterase and glutathione-S-transferase, were massively expanded in this polyphagous species, enabling its extraordinary ability to detect and detoxify many plant secondary compounds. Larval exposure to insecticidal toxins induced expression of detoxification genes, and knockdown of representative genes using short interfering RNA (siRNA) reduced larval survival, consistent with their contribution to the insect’s natural pesticide tolerance. A population genetics study indicated that this species expanded throughout southeast Asia by migrating along a South India–South China–Japan axis, adapting to wide-ranging ecological conditions with diverse host plants and insecticides, surviving and adapting with the aid of its expanded detoxification systems. The findings of this study will enable the development of new pest management strategies for the control of major agricultural pests such as S. litura.

Insect growth and development are intricately regulated by the titers of juvenile hormones (JHs) and ecdysteroids (and͞or their metabolites) in the insect hemolymph. Hydrolysis of the methyl ester of JH by a JH-specific esterase (JHE) is a key pathway for the degradation of JH. Here, we generate transgenic silkworm strains that overexpress JHE by using the binary GAL4͞UAS system. Overexpression of JHE from the embryonic stage resulted in larval-pupal metamorphosis after the third stadium, two stadia earlier than that observed in wild-type insects. This precocious metamorphosis suggests that JHs are not critical for normal development of embryo or larva before the second molt in Lepidoptera (moths and butterflies). Our transgenic approach allowed us to dissect the function of key physiological events that occur from embryogenesis. Until now, these types of studies were possible only in later larval stadia by using physical techniques such as allatectomy or the application of JH analogues. We believe that our system will allow further pioneering studies in insect physiology.Bombyx mori ͉ juvenile hormones ͉ transgenesis T wo major groups of nonpeptidic hormones, juvenile hormones (JHs) and ecdysteroids, play critical roles in the regulation of insect growth and development (1). The presence of JH during exposure to the ecdysteroids ensures a molt to a like stage, whereas the absence of JH during an ecdysteroid pulse allows metamorphosis. Concentrations of both hormones are regulated precisely by biosynthesis and degradation. Two definitive primary pathways for JH metabolism, hydrolysis of the methyl ester of JH by soluble esterases and hydration of the epoxide by microsomal epoxide hydrolases, have been described so far (2-5). In several insect orders, the key route of JH metabolism is by means of the hydrolysis of the methyl ester, and JH esterase (JHE) is considered the principal enzyme responsible for this function (2). Because of their importance in insect development, JHEs have been isolated and characterized from many insect orders such as Coleoptera (6), Diptera (7), and Lepidoptera (8-10), including the silkworm, Bombyx mori (11).As the primary degradative enzyme of JH, JHE has been used as an attractive tool for the study of JH action. Inhibition of JHE activity by a variety of 3-substituted 1,1,1-trifluoropropanone sulfides reduces the rate of JH degradation, thus delaying metamorphosis and resulting in giant larvae of Manduca sexta (12). By contrast, recombinant baculoviruses expressing JHE can reduce JH levels in Lepidoptera (13). However, difficulties in establishing stable and prompt in vivo expression of JHE in Lepidoptera have halted further studies.The mechanism of JH action in insects still remains a mystery despite a great deal of knowledge about its biological actions (5). Using Drosophila as a model for the study of JH action meets with difficulties because, in contrast to most insects, including those in Lepidoptera, Drosophila displays few morphogenetic actions that can be easily bioassayed ...

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Forkhead box O (FOXO) functions as the terminal transcription factor of the insulin signaling pathway and regulates multiple physiological processes in many organisms, including lifespan in insects. However, how FOXO interacts with hormone signaling to modulate insect growth and development is largely unknown. Here, using the transgene-based CRISPR/Cas9 system, we generated and characterized mutants of the silkworm FOXO () to elucidate its physiological functions during development of this lepidopteran insect. The mutant (FOXO-M) exhibited growth delays from the first larval stage and showed precocious metamorphosis, pupating at the end of the fourth instar (trimolter) rather than at the end of the fifth instar as in the wild-type (WT) animals. However, different from previous reports on precocious metamorphosis caused by juvenile hormone (JH) deficiency in silkworm mutants, the total developmental time of the larval period in the FOXO-M was comparable with that of the WT. Exogenous application of 20-hydroxyecdysone (20E) or of the JH analog rescued the trimolter phenotype. RNA-seq and gene expression analyses indicated that genes involved in JH degradation but not in JH biosynthesis were up-regulated in the FOXO-M compared with the WT animals. Moreover, we identified several FOXO-binding sites in the promoter of genes coding for JH-degradation enzymes. These results suggest that FOXO regulates JH degradation rather than its biosynthesis, which further modulates hormone homeostasis to control growth and development in In conclusion, we have uncovered a pivotal role for FOXO in regulating JH signaling to control insect development.