Individual and social immunisation in insects

• The immune systems of invertebrates show features characteristic of immune memory.
• The molecular mechanisms underlying these features are an area of active investigation.
• Insect immune memory can be highly specific and can be transferred across generations.
• Immune memory can act at the individual level and at the level of insect societies.

Immune systems are able to protect the body against secondary infection with the same parasite. In insect colonies, this protection is not restricted to the level of the individual organism, but also occurs at the societal level. Here, we review recent evidence for and insights into the mechanisms underlying individual and social immunisation in insects. We disentangle general immune-protective effects from specific immune memory (priming), and examine immunisation in the context of the lifetime of an individual and that of a colony, and of transgenerational immunisation that benefits offspring. When appropriate, we discuss parallels with disease defence strategies in human societies. We propose that recurrent parasitic threats have shaped the evolution of both the individual immune systems and colony-level social immunity in insects.