Monday, December 11, 2006 - 10:11 AM

The effect of parasitism by Cotesia congregata on the hemocytes of Diatraea saccharalis and Ostrinia nubilalis

James M. Termini, and Marianne Alleyne, University of Illinois - Urbana/Champaign, Department of Entomology, 320 Morrill Hall, 505 S. Goodwin Ave, Urbana, IL

In the insect community, the responses to parasitism are greatly varied. Two lepidopteran species, D. saccharalis and O. nubilalis, which are very closely related, show two distinct and completely opposite responses to parasitism by C. flavipes. D. saccharalis is known to be a suitable host (no encapsulation) while O. nubilalis will completely encapsulate all C. flavipes eggs within hours. This leaves one to wonder, what is responsible for this phenomenon. To try to answer this question flow cytometry was used to determine differences in the count of the two most abundant hemocytes (granular cells and plasmatocytes) in the two host species at different time points after parasitization. Fluorescent markers were used to distinguish the two types of hemocytes from each other. To insure proper labeling of the hemocytes, fluorescent marker binding was checked using microscopy. Two different fluorescent markers were used for flow cytometry; Peanut Agglutinin (PNA-FITC), and Propidium Iodide (PI). PNA-FITC was found to label the granular cells more intensely, with minimal staining of plasmatocytes. PI is a nuclear label that was used to distinguish the ploidy of the cells. Flow cytometry was performed on samples of D. saccharalis and O. nubilalis hemolymph that were fluorescently labeled. There was a significant difference in total and differential hemocyte counts between the two species. Significant differences were found when comparing the hemocyte composition of the control samples and samples from hosts that had been previously parasitized by C. flavipes.

Species 1: Hymenoptera Braconidae Cotesia congregata
Species 2: Lepidoptera Crambidae Diatraea saccharalis (sugarcane borer)
Species 3: Lepidoptera Crambidae Ostrinia nubilalis (European corn borer)