Insect small non-coding RNA involved in epigenetic regulations

•A consensus is emerging regarding the role of small RNAs in epigenetic control.•In Drosophila, some small RNAs can guide heterochromatin formation.•A conserved post-transcriptional pathway represses transposable elements.•In Drosophila, small RNAs carry extrachromosomal transgenerational information. Small regulatory RNAs can not only guide post-transcriptional repression of target genes, but some of them can also direct heterochromatin formation of specific genomic loci. Here we review the published literature on small RNA-guided epigenetic regulation in insects. The recent development of novel analytical technologies (deep sequencing and RNAi screens) has led to the identification of some of the factors involved in these processes, as well as their molecular mechanism and subcellular localization. Other findings uncovered an additional mode of epigenetic control, where maternally inherited small RNAs can affect phenotypes in a stable, transgenerational manner. The evolutive history of small RNA effector proteins in insects suggests that these two modes of regulation are variably conserved among species.