Insect immunity against microsporidia

Microsporidia are a group of fungi-related, unicellular eukaryotic parasites that, over the course of their long evolutionary history, have colonized a wide range of hosts from other unicellular organisms to mammals. A significant portion of the described microsporidian species infect insects, including economically important ones such as honeybees and silkworms. Microsporidia infect representatives of all insect orders, and their diversification often parallels that of their hosts. Their widespread distribution among insects suggests an ability to overcome host defense mechanisms. This review summarizes the latest findings on how the insect immune system responds to microsporidian infections and how these parasites evade key immune defenses. Insect defense mechanisms — including behavioral responses in social insects, physical barriers in the intestine, and the production of antimicrobial peptides — appear to be of limited effectiveness against microsporidia, due to the unique features of their life cycle and spore structure. However, key immune responses such as apoptosis of infected cells, oxidative stress, and hemocyte-mediated reactions like melanization play a crucial role in defending insects against these parasites.