Abstract

Effect of parasitism of Diatraea saccharalis (Lepidoptera: Crambidae) larvae by the wasp Cotesia flavipes (Hymenoptera: Braconidae) in defense reactions against abiotic agents: production and encapsulation reaction

This study aimed to determine prophenoloxidase (proPO) activation and nitric oxide (NO) production in the hemolymph of Diatraea saccharalis larvae non-parasitized and parasitized by the wasp Cotesia flavipes and/or inoculated with abiotic agent (Sephadex beads), during parasitism/inoculation, and related to larval age; the ultrastructure of the capsule formed around the abiotic agent during parasitism was also examined. D. saccharalis larvae at 20 days of development (5th-instar larvae) were parasitized by C. flavipes. After different times of parasitism and/or inoculation with the abiotic agent (2 and 6 h, and 3 and 6 days), the sugarcane borer hemolymph was collected and frozen at -20°C for later analyses of in vitro proPO system activation and NO production. To observe the encapsulation response to the abiotic agent implant, the Sephadex beads were recovered and conventionally prepared for ultrastructural analyses. There was a significant reduction in both the activation of the proPO system and in NO production of D. saccharalis non-parasitized/inoculated larvae related to larval development, from 20 to 26 days. The parasitism by C. flavipes inhibited proPO system activation during the whole experimental time; NO production was inhibited only at initial (2 h) and early (6 h) parasitism. The inoculation of non-parasitized larvae with Sephadex beads increased proPO system activation, at all experimental times, but it did not increase the NO production of these larvae. The parasitism of D. saccharalis larvae by C. flavipes concomitant with their inoculation with Sephadex beads significantly inhibited the activation of the proPO system, but it did not affect NO production levels at all times studied. The D. saccharalis larvae parasitized by C. flavipes were able to identify and encapsulate the Sephadex beads as the non-parasitized insects, based on ultrastructural analyses. Therefore, our results indicate that although there was an inhibition of the proPO system due to parasitism, the Sephadex beads were recognized as non-self and encapsulated, but the parasitoid was not recognized and successfully developed in the insect host hemocele. The hemocyte responsible for proPO synthesis in D. saccharalis was the oenocytoid; it was impossible to determine the hemocyte type responsible for NO production.

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