Characterisation of immune responses in the pea aphid, Acyrthosiphon pisum

► Pea aphids have three haemocyte types: prohaemocytes, granulocytes and oenocytoids. ► Prohaemocyte numbers increase immediately after an immune challenge. ► Pea aphids exhibit melanotic but not cellular encapsulation response. ► Pea aphids can phagocytose both Gram positive and Gram negative bacteria.