Identification and quantification of the most abondant hemocytes in the pine processionary caterpillar;Thaumetopoeapityocampa (Notodontidae)

Thaumetopoeapityocampa is an important pine pest in the Mediterranean basin and central Europe. The insecte is a butterfly, whose larvae are called pine processionary caterpillars. To understand the resistance mechanism of the insect in order to proceed of its control and to diminuate their effect in nature, it was necessary to study of the immune system and reactions of the larva in different stages. The aim of our work is to identify the hemocytes formula of the caterpillar during the larval stages L2, L3, and L4, as well as the quantification of the different cells during each stage. After extraction of the hemolymph by centrifugation, the cells were placed in culture medium and then incubated. Microscopic observation has shown that prohemocytes population appear early in hemolymph, they differentiate into plasmatocytes and granulocytes during the advanced stages. However, the quantification process (THC), carried out in a Malassez counting chamber has shown that granulocytes are the most abundant cell population in the hemolymph of the insect larvae. To investigate the role of hemocytes in immune responses, we have co-incubate T. pityocampa cells with bacteria, entomopathogenic nematodes, and synthetic beads. Both humoral and cellular encapsulation processes have been observed early in larval stages, all hemocytes seem to be involved in the formation of nodules and capsules against bacteria and microbeads. At the opposite, entomopathogenic nematodes (Steinernemafeltiae) were not recognized and encapsulated, but their presence can strongly damage host hemocytes.