Hemocytes are involved in conferring a cellular, or hemocytic, immunity to insects. These cells are formed in haemopoietic organs that are variously well developed in different insect groups. In the cricket Gryllus haemopoietic organs are well developed, distinct organs found in the second and third abdominal segments along either side of the heart. In other insects haemopoietic organs are amorphous clumps of cells irregularly distributed along the dorsal vessel. PLs are capable of phagocytosis, a kind of entocytosis of smaller foreigh cells.
Phagocytosis usually follows low doses of invading yeast and bacteria.
PLs are also involved in encapsulation of clumps of invading microbes. There are typically more PLs than other types of hemocytes. Electron microscope studies have revealed differences among the granules in these cells. There are structureless and structured granules. The biochemistry of the different types of granules is not yet understood.