The increasing availability of insect genomes has revealed a large number of genes with unknown functions and the resulting problem of how to discover these functions. The RNA interference (RNAi) technique, which generates loss-of-function phenotypes by depletion of a chosen transcript, can help to overcome this challenge. RNAi can unveil the functions of new genes, lead to the discovery of new functions for old genes, and find the genes for old functions. Moreover, the possibility of studying the functions of homologous genes in different species can allow comparisons of the genetic networks regulating a given function in different insect groups, thereby facilitating an evolutionary insight into developmental processes. RNAi also has drawbacks and obscure points, however, such as those related to differences in species sensitivity. Disentangling these differences is one of the main challenges in the RNAi field.

The mevalonate pathway in insects has two important peculiarities, the absence of the sterol branch and the synthesis of juvenile hormone (JH), that may have influenced the mechanisms of regulation. The data available on these mechanisms indicate that cholesterol does not play a regulatory role and that JH modulates transcript levels of a number of genes of the mevalonate pathway or can influence the translatability and/or stability of the transcripts themselves. These data suggest that the mevalonate pathway in insects can best be interpreted in terms of coordinated regulation, in which regulators act in parallel to a number of enzymes, as occurs in the cholesterol-driven pathway in vertebrates.

E usociality, the reproductive division of labour with overlapping generations and cooperative brood care, is one of the major evolutionary transitions in biology 1 . Although rare, eusociality has been observed in a diverse range of organisms, including shrimps, mole rats and several insect lineages [2][3][4] . A particularly striking case of convergent evolution occurred within the holometabolous Hymenoptera and in the hemimetabolous termites (Isoptera), which are separated by over 350 Myr of evolution 5 . Termites evolved within the cockroaches around 150 Myr ago, towards the end of the Jurassic period 6,7 , about 50 Myr before the first bees and ants appeared 5 . Therefore, identifying the molecular mechanisms common to both origins of eusociality is crucial to understanding the fundamental signatures of these rare evolutionary transitions. While the availability of genomes from many eusocial and non-eusocial hymenopteran species 8 has allowed extensive research into the origins of eusociality within ants and bees [9][10][11] , a paucity of genomic data from cockroaches and termites has precluded large-scale investigations into the evolution of eusociality in this hemimetabolous clade.The conditions under which eusociality arose differ greatly between the two groups. Termites and cockroaches are hemimetabolous and so show a direct development, while holometabolous hymenopterans complete the adult body plan during metamorphosis. In termites, workers are immatures and only reproductive castes are adults 12 , while in Hymenoptera, adult workers and queens represent the primary division of labour. Moreover, termites are diploid and their colonies consist of both male and female workers, and usually a queen and king dominate reproduction. This is in contrast to the haplodiploid system found in Hymenoptera, in which all workers and dominant reproductives are female. It is therefore intriguing that strong similarities have evolved convergently within the termites and the hymenopterans, such as differentiated castes and a nest life with reproductive division of labour. The termites can be subdivided into wood-dwelling and foraging termites. The former belong to the lower termites and produce simple, small colonies with totipotent workers that can become reproductives. Foraging termites (some lower and all higher termites) form large, complex societies, in which worker castes can be irreversible 12 . For this reason, higher, but not lower, termites can be classed as superorganismal 13 . Similarly, within Hymenoptera, varying levels of eusociality exist.Here we provide insights into the molecular signatures of eusociality within the termites. We analysed the genomes of two lower and one higher termite species and compared them to the genome

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