ABSTRACT

The ability to form multiple discrete phenotypes from a single genotype is known as polyphenism. Such phenotypic plasticity is prevalent in social insects, where environmental stimuli trigger distinct phenotypes, e.g., the different castes of honeybees and ants (Miura 2005, Judice et al. 2006, Johnson 2010). Other insects, such as butterfl ies, respond to seasonal changes in temperature and photoperiod by adapting their pigmentation. The map butterfl y Araschnia levana provides a striking example of seasonal polyphenism because spring adults are predominantly orange whereas summer adults are black and white (Morehouse et al. 2013). Several pest insects respond to biotic and abiotic stress by modifying physiological parameters including their reproductive strategy, and in this context aphids provide an ideal model system to study seasonal polyphenism (Srinivasan and Brisson 2012). It is becoming increasingly evident that seasonal polyphenism in insects is achieved by the epigenetic regulation of transcriptional reprogramming. The molecular basis of polyphenism in aphids and other insects therefore relies largely on the study of DNA methylation, histone acetylation and the synthesis of microRNAs (miRNAs) that epigenetically regulate gene expression.