Department of Entomology

Gregory Walker

Professor of Entomology

Location: University Lab Building 201

Research Specialization

Our lab is engaged in two general areas of research: insect-plant interactions with a focus on piercing-sucking insects such as whiteflies, aphids, leafhoppers and thrips; and mechanisms of plant pathogen transmission by these insects.  All of these insects are major agricultural pests.  They not only inflict crop loss by their feeding on plants but also, most plant viruses are transmitted by piercing-sucking insects.

 Piercing-Sucking Insect-Plant Interactions.  Because piercing-sucking insects can pick and choose which plant tissues and cells on which to feed, the physiological interactions between piercing-sucking insects and plants are much more intricate than they are for chewing insects, making this a particularly interesting area of study.   The overall goal of our research is to identify and understand mechanisms by which plants can be resistant to these insects.  Studies in our lab vary from the very applied level of identifying resistant plant genotypes, to the basic level of determining mechanisms of resistance.  Our research encompasses field and greenhouse studies screening plants for resistance, and detailed laboratory studies on feeding behavior, the physiological response of the plants to insect feeding, and the responses of the insects to plant defenses.  In one current project, we are examining the molecular responses of the model plant Arabidopsis thaliana to whitefly feeding, and how the whiteflies respond to mutant plants with altered molecular defense responses.   In another current project, we are examining how phloem-feeding insects such as aphids and whiteflies are able to circumvent the plant's normal response to phloem damage, which is to seal up damaged phloem sieve tubes (analogous to animal blood clotting in response to damage to a blood vessel).  We also will be exploring whether or not variations in phloem sealing defense response can be used to provide resistance to these insects.

 Mechanisms of Plant Pathogen Transmission by Insect Vectors.  Most plant viruses exploit the mobility and feeding behavior of piercing-sucking insects in order to be transmitted from one plant to another.  Our lab has been involved in several projects to determine the specific part of feeding behavior that results in inoculation of plant viruses by piercing-sucking insect vectors.  Additionally, we recently have completed a project that demonstrated Tomato Spotted Wilt Virus alters the feeding behavior of its thrips vector in a way that favored transmission of the virus.  Finally in a current project, we have identified the viral capsid protein that is responsible for Lettuce Infectious Yellows Virus to bind to its whitefly vector; without this specific binding, virus transmission will not occur.

Degrees

BA Zoology 1975

Miami University, Oxford, OH

MS Entomology 1979

Ohio State University

PhD Entomology 1982

Ohio State University

Publications

Recent Publication

Chen, A. Y. S., G. P. Walker, D. Carter and J. C. K. Ng 2011. A virus capsid component mediates virion retention and transmission by its insect vector. Proceedings of the National Academy of Sciences 108: 16777-16782.

Stafford, C. A., G. P. Walker & D. E. Ullman. 2011. Infection with a plant virus modifies vector feeding behavior. Proceedings of the National Acedemy of Sciences 108: 9350-9355.

Tena, A., A. Kapranis, G. P. Walker, F. Garcia-Mari & R. F. Luck. 2011. Larval morphology of Metaphycus flavus and its role in host attachment and larval cannibalism. Bulletin of Entomological Research 101: 365-372.

Walker, G. P., T. M. Perring & T. P. Freeman. 2010. Life history, functional anatomy, feeding and mating behavior. In Stansly, P. A. & S. Naranjo (eds.) Bemisia: Bionomics and Management of a Global Pest. Springer.  pp. 109-160.

Magsig-Castillo, J., J. G. Morse, G. P. Walker, J. L. Bi, P. F. Rugman-Jones & R. Stouthamer. 2010. Phoretic dispersal of armored scale crawlers (Hemiptera: Diaspididae).  Journal of Economic Entomology 103: 1172-1179.

Gill, R. J., G. P. Walker & J. Y. Honda. 2010. Redescription of two live oak-infesting whiteflies in California. Pan Pacific Entomologist 86: 72-91.

Stafford, C. A. & G. P. Walker. 2009.  Characterization and correlation of DC electrical penetration graph waveforms with feeding behavior of beet leafhopper, Circulifer tenellus. Entomologia Experimentalis et Applicata 130: 113-129.

Stafford, C. A, G. P. Walker & R. Creamer. 2009. Stylet penetration behavior resulting in inoculation of Beet severe curly top virus by beet leafhopper, Circulifer tenellus. Entomologia Experimentalis et Applicata 130: 130-137.

Backus, E. A., W. J Holmes, F. Schreiber, B. J. Reardon &  G. P. Walker. 2009. Sharpshooter X wave: Correlation of an electrical penetration graph waveform with xylem penetration supports a hypothesized mechanism for Xylella fastidiosa inoculation. Annals of the Entomological Society of America 102: 847-867.

Bayoun, I. M., G. P. Walker & S. V. Triapitsyn. 2008. Parasitization of beet leafhopper eggs, Circulifer tenellus, in California. Journal of Applied Entomology 132: 412-424.

Walker, G. P., C. A. Stafford, E. J. Symmes & R. Goh. 2008. Phenology and descriptions of two sympatric native whiteflies (Hemiptera: Aleyrodidae) with a high degree of niche overlap. Pan Pacific Entomologist 84: 36-50.

Kasetty, S., C. Stafford, G. P. Walker, X. Wang & E. Keogh. 2008.  Real-time classification of streaming sensor data. 20th IEEE International Conference on Tools with Artificial Intelligence 149-156 

Symmes, E. J., G. P. Walker & T. M. Perring. 2008. Stylet penetration behaviors of Myzus persicae related to transmission of Zucchini yellow mosaic virus.  Entomologia Experimentalis et Applicata 129: 258-267.

Jiang, Y. X. & G. P. Walker.  2007.  Identification of phloem sieve elements as the site of resistance to silverleaf whitefly in resistant alfalfa genotypes.  Entomologia Experimentalis et Applicata. 125: 307-320.

Walker, G. P. & E. T. Natwick.  2006.  Resistance to silverleaf whitefly, Bemisia argentifolii (Hem., Aleyrodidae), in Gossypium thurberi, a wild cotton species.  Journal of Applied Entomology 130: 429-436.

Walker, G. P., I. M. Bayoun, S. V. Triapisyn & J. Y. Honda.  2005.  Taxonomy of Aphelinoidea (Hymenoptera: Trichogrammatidae) species attacking eggs of the beet leafhopper, Circulifer tenellus (Hemiptera: Cicadellidae), in California.  Zootaxa 1068: 1-25.

Jiang, Y. X., N. Zareh, G. P. Walker and L. R. Teuber. 2003.  Characterization of alfalfa germplasm expressing resistance to silverleaf whitefly, Bemisia argentifolii. Journal of Applied Entomology.  127: 447-457.

Jiang. Y. X. & G. P. Walker.  2003.  Electrical penetration graphs of the nymphal stage of Bemisia argentifolii.  Entomologia Experimentalis et Applicata  109: 101-111.

Johnson, D. D., G. P. Walker, and R. Creamer.  2002.  Stylet penetration resulting in inoculation of a semipersistently transmitted closterovirus by the whitefly Bemisia argentifolii. Entomologia Experimentalis et Applicata 102: 115-123.

 Luft, P. A., T. D. Paine, and G. P. Walker.  2001.  Interactions of colonisation density and leaf environments on survival of Trioza eugeniae nymphs. Ecological Entomology 26: 263-270.

Jiang, Y. X. and G. P. Walker.  2001.  Pathway phase waveform characteristics correlated with length and rate of stylet advancement and partial stylet withdrawal in AC electrical penetration graphs of adult whiteflies. Entomologia Experimentalis et Applicata 101: 233-246.

Al-Wahaibi, A. K. and G. P. Walker.  2000.  Searching and oviposition behavior of a mymarid egg parasitoid, Anagrus nigriventris, on five host plant species of its leafhopper host, Circulifer tenellus. Entomologia Experimentalis et Applicata 96: 9-25.

Al-Wahaibi, A. K. and G. P. Walker.  2000.  Oviposition behavior of Anagrus nigriventris, an egg parasitoid of beet leafhopper, Circulifer tenellus.  BioControl 45: 139-153.

Chu, C. C., T. P. Freeman, J. S. Buckner, T. J. Henneberry, D. R. Nelson, G. P. Walker, and E. T. Natwick.  2000.  Bemisia argentifolii (Homoptera: Aleyrodidae) colonization on upland cottons and relationships to leaf morphology and leaf age.  Annals of the Entomological Society of America 93: 912-919.