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.

▪ Abstract 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.

Around 150 million years ago, eusocial termites evolved from within the cockroaches, 50 million years before eusocial Hymenoptera, such as bees and ants, appeared. Here, we report the 2-Gb genome of the German cockroach,Blattella germanica, and the 1.3-Gb genome of the drywood termiteCryptotermes secundus. We show evolutionary signatures of termite eusociality by comparing the genomes and transcriptomes of three termites and the cockroach against the background of 16 other eusocial and non-eusocial insects. Dramatic adaptive changes in genes underlying the production and perception of pheromones confirm the importance of chemical communication in the termites. These are accompanied by major changes in gene regulation and the molecular evolution of caste determination. Many of these results parallel molecular mechanisms of eusocial evolution in Hymenoptera. However, the specific solutions are remarkably different, thus revealing a striking case of convergence in one of the major evolutionary transitions in biological complexity.