Nancy E. Beckage
Professor of Entomology & Cell Biology and Neuroscience
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Biochemical Host-Parasite Relationships Insect Endocrinology
Ph.D. in Zoology, University of Washington, Seattle, 1980
VOICE: 951-827-3521 |
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My laboratory studies host-parasite and host-pathogen relationships in insect hosts. We use the tobacco hornworm, Manduca sexta, and its interactions with the wasp parasite Cotesia congregata as a model system for examining molecular and biochemical host-parasite interactions. This parasite, like other braconid and ichneumonid wasps, injects a large, multi-segmented DNA virus, a polydnavirus, into the host during parasitization. Viral sequences are integrated in the genomic DNA of the parasite and the PDV is a symbiont of the wasp. The polydnavirus replicates in the reproductive tract of the female wasp, and virus replication causes the cells of the ovarian calyx to lyse, releasing the virions into the lumen of the ovary, where they co-mingle with parasite eggs. Following oviposition, the virions enter host cells and become transcriptionally active.
The role of the polydnavirus during parasitism appears to be to cause host immunosuppression, which allows the parasites to develop without becoming encapsulated by host hemocytes. One of the viral transcripts, Early Protein 1 (EP1), is produced in all permissive hosts of the parasites, but not nonpermissive species, suggesting its production is correlated with successful development of the parasite in the host. We are studying the role of EP1 and other viral transcripts in the biochemical interaction between the host insect and its parasites. The mechanisms of host immunosuppression, and how parasitism alters humoral and cell-mediated immune responses, are of special interest. Endocrine host-parasite relationships coordinate the development of parasite and host. Following wasp oviposition into early instar caterpillars, the parasites develop through two instars then emerge from a fifth instar host. The host is induced to undergo developmental arrest in the larval stage, and does not proceed to metamorphosis. We are examining the endocrine mechanisms involved in causing host developmental arrest, focusing on hemolymph juvenile hormone and ecdysteroid titers. We are also investigating neuropeptides that regulate activity of the glands producing these hormones. The parasites secrete ecdysteroids, causing an ecdysteroid peak to occur in the hemolymph the day before the wasps emerge from the host. The ecdysteroid titer then falls to a low basal level which prevents further molting. The JH titer is high, and JH esterase levels are nondetectable. Thus, the high JH mileu prevents metamorphosis. Neuropeptides accumulate in the brain, retrocerebral complex, and ventral nerve cord of the host, wihout being released. The prothoracic glands therefore remain inactive, and ecdysteroid is not produced during the period of developmental arrest. |
 A tobacco hornworm larva with emerging Cotesia congregata wasp parasites |
SELECTED PUBLICATIONS
Washburn, J.O., Haas-Stapleton, E.J., Tan, F.F., Beckage, N.E. and L.E. Volkman. Co-infection of Manduca sexta larvae with polydnavirus from Cotesia congregata increases susceptibility to fatal infection by Autographa californica M nucleopolyhedrovirus. Journal of Insect Physiology 46: 179-190 (2000).
Savary, S., Drezen, J.-M., Tan, F., Beckage, N.E. and G. Periquet. The excision of polydnavirus sequences from the genome of the wasp Cotesia congregata (Braconidae, Microgastrinae) is developmentally regulated but not strictly restricted to the ovaries in the adult. Insect Molecular Biology 8: 319-327 (1999).
Beckage, N.E. Insect growth regulators. In "Biological and Biotechnological Control of Insect Pests" (Eds. J.E. Rechcigl and N.A. Rechcigl), pp. 123-137 (CRC Press) (1999).
Beckage, N.E. Modulation of immune responses to parasitoids by polydnaviruses. Parasitology 116: S57-S64 (1998).
Beckage, N.E. Parasitoids and polydnaviruses. Bioscience 48: 305-310 (1998).
Harwood, S.H., McElfresh, J.S., Nguyen, A., Conlan, C.A. and N.E. Beckage. Production of early expressed parasitism-specific proteins in alternate sphingid hosts of the braconid wasp Cotesia congregata. Journal of Invertebrate Pathology 71: 271-279 (1998).
Kelly, T.J., Gelman, D.B., Reed, D.A. and N.E. Beckage. Effects of parasitization by Cotesia congregata on the brain-prothoracic gland axis of its host, Manduca sexta. Journal of Insect Physiology 44: 323-332 (1998).
Beckage, N.E. The parasitic wasp's secret weapon . Scientific American 277: 50-55 (1997).
Beckage, N.E. (Ed.) "Parasites and Pathogens: Effects on Host Hormones and Behavior" (Chapman and Hall) (1997).
Adamo, S.A., Linn, C.E. and Beckage, N.E. Correlation between changes in host behavior and octopamine levels in the tobacco hornworm parasitized by the braconid wasp Cotesia congregata. Journal of Experimental Biology 200:117-127 (1997).
Savary, S., Beckage, N.E., Tan, F., Periquet, G. and J.-M. Drezen. Excision of the polydnavirus chromosomal integrated EP1 sequence of the parasitoid wasp Cotesia congregata at potential recombinase binding sites. Journal of General Virology 78: 3125-3134 (1997).