Irradiation and parasitism affect the ability of larval hemocytes of Anastrepha obliqua for phagocytosis and the production of reactive oxygen species

The development of the parasitoid Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae) in Anastrepha obliqua (McQuart) (Diptera: Tephritidae) larvae is unviable in nature; however, if the host larva is irradiated at 160 Gy, the parasitoid develops and emerges successfully. This suggests that radiation affects the immune responses of A. obliqua larvae, while the underlying mechanisms remain to be revealed. Using optical and electronic microscopies we determined the number and type of hemocyte populations found inside the A. obliqua larvae, either nonirradiated, irradiated at 160 Gy, parasitized by D. crawfordi, or irradiated and parasitized. Based on flow cytometry, the capacity to produce reactive oxygen species (ROS) was determined by the 123-dihydrorhodamine method in those hemocyte cells. Five cell populations were found in the hemolymph of A. obliqua larvae, two of which (granulocytes and plasmatocytes) can phagocytize and produce ROS. A reduction in the number of cells, mainly of the phagocytic type, was observed, as well as the capacity of these cells to produce ROS, when A. obliqua larvae were irradiated. Both radiation and parasitization decreased the ROS production, and when A. obliqua larvae were irradiated followed by parasitization by D. crawfordi, the reduction of the ROS level was even greater. In contrast, a slight increase in the size of these cells was observed in the hemolymph of the parasitized larvae compared to those in nonparasitized larvae. These results suggest that radiation significantly affects the phagocytic cells of A. obliqua and thus permits the development of the parasitoid D. crawfordi.