Parasitism by Cotesia flavipes alters the hemocyte population and humoral immunity of the sugarcane borer, Diatraea saccharalis

Parasitism of a crambid, Diatraea saccharalis larvae by the braconid wasp Cotesia flavipes or injection of C. flavipes polydnavirus (CfPDV) causes numerous alterations in host physiology, including developmental arrest, abrogation of host immunity, and biochemical changes in proteins, carbohydrates, glycogen and lipids. This study focused on changes of cellular immunity in the parasitized D. saccharalis in terms of hemocyte composition. Also we analyzed the effects of parasitization by C. flavipes on humoral immunity in parasitized D. saccharalis in terms of phenoloxidase and lysozyme activities. In nonparasitized D. saccharalis larvae, granular cells represented the main hemocyte type (35%) and plasmatocytes were also present at around 30% among the total hemocytes. Following parasitization by C. flavipes, the relative proportions of these two major hemocytes changed very little, but the total hemocyte counts exhibited a significant reduction in parasitized larvae. The parasitized larvae showed significant decrease in total hemolymph proteins after 8 days of parasitization. They also showed a significant decrease in humoral immune capacity as evidenced by reduction of phenoloxidase and lysozyme activity. This research demonstrates that the parasitism of C. plutellae adversely affects the total hemocyte populations in number and function, which would contribute to host immunosuppression.