CRIS Project Title:   Management of insect pests of ornamental trees and shrubs

INTRODUCTION:  Entomology research experience involves: the nutritional ecology and physiology of herbivorous insects on plants and implications to natural enemies, plant effect on host insect quality and its consequences for biological control, manipulation of the biological environment for insect pest suppression (i.e., host plant resistance to pest insects, mechanism of resistance, factors affecting resistance), environmental manipulations and cultural practices for insect pest suppression (i.e., changes in the environment adversely affecting the pest, and changes in the environment encouraging natural enemies), genetic manipulation for insect pest suppression (i.e., genetic manipulation of pest populations and genetic improvement of beneficial organisms), establishment and implementation of Biological Control and Integrated Pest Management programs in greenhouses for the control of insect pests on vegetables and ornamentals, development of novel strategies for insecticide resistance management, taxonomical identification of leafhoppers, treehoppers and spittlebugs associated with shade trees, and pathogen detection in insect vectors.

PROJECT SUMMARY:  Current project aims to determine the insect vectors of the causal agent of bacterial leaf scorch of shade trees. Presently, there is neither any effective therapy for trees and shrubs infected with Xylella fastidiosa, nor a strategy for preventing infection. Thus, identification of the insect vector(s) will facilitate designing the proper experiments to elucidate the relationship among insect vectors and bacterial leaf scorch. It is the long-term goal of the Entomology Program, in collaboration with partner scientists, to generate the needed data to develop disease and vector management strategies.

This project alsoaims to develop and test Integrated Pest Management (IPM) tactics for managing populations of the potato leafhopper infesting maples, and the azalea lace bug infesting azaleas. Use of IPM tactics provides alternatives for reducing damage from these pest insects in ways that would be less expensive and less threatening to the environment than applying high-risk insecticides. Thus, product quality and market competitiveness would be improved in a cost-effective manner. Data are lacking on such aspects as the use of resistant plant material, scouting and monitoring programs, application of biorationals or reduced-risk insecticides, plant health care, release and efficacy of natural enemies, and habitat manipulation as related to insect pests of shade trees and woody plants. Thus, by trying to modify current IPM practices from other crops, and adopting them to be used on shade trees, new concepts for application to shade trees would be developed.

PROGRESS:   Because light has a marked influence on the growth of azaleas, the performance of the azalea lace bug on plants growing under sunlight or shade has been the focus of several studies with conflicting results. This study proved that shading is not a good indicator of host acceptability for oviposition or host suitability for nymphal survivorship, or a good predictor of population numbers. First to show that the behavior or performance of the azalea lace bug is influenced by the nutritional quality of the host plant, and not related to predation. This study showed that control decisions should be based on the degree of feeding injury caused by the insect and not based on population numbers.

Although the potato leafhopper is a polyphagous insect that has been reared on nearly 200 kinds of plants, it is not known why some trees are consumed by this insect and others are not. Determined that resistance against the potato leafhopper is related, in part, to the leaf content of important nutritional elements. Determined that American elm, red maple and Freeman maple have different mechanisms of resistance against the potato leafhopper. First to show that because elms do not show feeding injury, they could present a problem when growing maples and elms in nurseries and when used in the diversification of the urbanscape as populations of the potato leafhopper could build-up on these to such an extent that they become an economic problem on other nontolerant hosts, such as red maple.

The potato leafhopper is a serious problem on red maple causing severe economic damage in nurseries and landscape settings. Yet, susceptibility in red maple to feeding injury by the potato leafhopper varies significantly among trees. Determined trees that begin growth earliest and develop mature leaves more rapidly sustain less leafhopper injury. Showed that the most tolerant clone sustained the lowest frequency of leafhoppers throughout the season. This research was the first report demonstrating the extent to which variation in susceptibility of red maple to potato leafhopper injury among clones is genetically controlled, and conditioned by leaf flush phenology and foliar element content.

Recent widespread recognition of X. fastidiosa as the causal agent of bacterial leaf scorch of a wide variety of woody ornamentals has revealed that this bacterium is spreading and becoming more severe in landscape trees. The vectors responsible for transmitting X. fastidiosa in shade trees have not been determined. Identified several leafhopper species as vectors of bacterial leaf scorch and decline of elms and oaks, i.e., Aulacizes irrorata, Oncometopia undata, Graphocephala coccinea, Graphocephala versuta, Draeculacephala mollipes. First to detect different species of treehoppers testing positive for X. fastidiosa. An understanding of the transmission of this bacterium by insect vectors is economically important because there is neither any known effective therapy for infected trees and shrubs nor a strategy for preventing infection.

Container production of maple is becoming an increasingly popular trend, following demands of the horticulture industry, but no attention has been paid to the susceptibility of container-grown maples to damage by the potato leafhopper. In collaboration with Dr. Alden Townsend (also of the Floral and Nursery Plants Research Unit) experiments were done in the laboratory, environmental chambers, and in the greenhouse using container-grown trees of three different red maple clonal selections from the USNA Tree Breeding Program and three Freeman maple cultivars to determine the effect of nitrogen fertilization on oviposition, survival and development of the potato leafhopper. This study showed that fertilization improved the performance of the potato leafhopper on previously nonpreferred maple selections, and that the foliar nutrient content and C:N ratio could be used as indicators of the susceptibility of container-grown trees to insect attack under different growing conditions. This research information will be used in the development of Integrated Pest Management strategies for the control of the potato leafhopper on container-grown trees.

PLANS:   In the year 2004 we will finish screening potential X. fastidiosa vectors, challenge commercial cultivars and USNA selections of elm with X. fastidiosa, and test reduced risk insecticides and biopesticides against the potato leafhopper and the azalea lace bug in field experiments.

In the year 2005 we will test the efficacy of leafhopper vectors in transmitting X. fastidiosa to elms and oaks, validate sampling plans for monitoring of the potato leafhopper, determine the effectiveness of insect predators against the azalea lace bug as mediated by shading exposure and azalea cultivar. In the year 2006 we will finish transmission experiments with vectors of X. fastidiosa, test the effectiveness of combining systematically treated trap plants with sampling plans against the potato leafhopper in the field, test the effectiveness of combining companion plans, biopesticides and predators in managing population and injury levels of the azalea lace bug.

The present CRIS is to be reviewed in 2004.

RECENT PUBLICATIONS: (1995-present)

1995. Bentz, J., Reeves, J., III, Barbosa, P. and Francis, B. The effect of nitrogen fertilizer on the selection, acceptance and suitability of Euphorbia pulcherrima (Euphorbiaceae) as a host plant to Bemisia tabaci (Homoptera: Aleyrodidae). Environ. Entomol. 24: 40 45.

1995. Bentz, J., Reeves, J., III, Barbosa, P. and Francis, B. Within plant variation in nitrogen and sugar content of poinsettia and its effects on the oviposition pattern, survival and development of Bemisia argentifolii (Homoptera: Aleyrodidae). Environ. Entomol. 24:271 277.

1995. Bentz, J., Reeves, J., III, Barbosa, P. and Francis, B. The effect of nitrogen fertilizer source and level on the ovipositional choice of poinsettia by the sweetpotato whitefly. J. Econ. Entomol. 88: 1388 1392.

1995. Bentz, J. and Neal, J. W., Jr. Effect of a natural insecticide from Nicotiana gossei on the whitefly parasitoid Encarsia formosa (Hymenoptera: Aphelinidae). J. Econ. Entomol. 88: 1611 1615.

1996. Kochansky, J., Hill, A., Neal, J. W., Jr., Bentz, J. and Roelofs, W. The Pheromone of the Eastern tent caterpillar, Malacosoma americanum (F.) (Lepidoptera, Lasiocampidae). J. Chem. Ecol. 22: 2251 2261.

1996. Bentz, J., Reeves, J., III, Barbosa, P. and Francis, B. The effect of nitrogen fertilizer applied to Euphorbia pulcherrima on the parasitization of Bemisia argentifolii by the parasitoid Encarsia formosa. Entomol. Exp. Appl. 78: 105 110.

1997. Neal, J. W., Jr., Chittams, J. L. and Bentz, J. Spring emergence by larvae of the Eastern tent caterpillar (Lepidoptera: Lasiocampidae): a hedge against high risk conditions. Ann. Entomol. Soc. Am. 90: 596 603.

1997. Neal, J. W., Jr. and Bentz, J. Physical dynamics of the noncleidoic egg of Stephanitis pyrioides (Heteroptera: Tingidae) during development. Environ. Entomol. 26: 1066 1072.

1997. Bentz, J. and Townsend, A. M. Variation in adult populations of the potato leafhopper (Homoptera: Cicadellidae) and feeding injury among clones of red maple. Environ. Entomol. 26: 1091 1095.

1997. Pooler, M. R., Myung, I. S., Bentz, J., Sherald, J. and Hartung, J. S. Detection of Xylella fastidiosa in potential insect vectors by immunomagnetic separation and nested polymerase chain reaction. Let. Appl. Microbiol. 25: 123 126.

1998. Bentz, J. W., Jr., Davis, J. C., Bentz, J., Warthen, J. D., Jr., Griesbach, R. J. and Santamour, F. S., Jr. Allelochemical activity in Ardisia species (Myrsinaceae) against selected arthropods. J. Econ. Entomol. 91: 608 617.

1999. Neal, J. W., Jr. and Bentz, J. Evidence for the stage inducing phenotypic plasticity in pupae of the polyphagous whiteflies Trialeurodes vaporariorum and Bemisia argentifolii (Homoptera: Aleyrodidae) and its raison d'etre. Ann. Entomol. Soc. Am. 92: 774 787.

1999. Bentz, J. and Townsend, A.M.. Feeding injury, oviposition and nymphal survivorship of the potato leafhopper on red maple and Freeman maple clones. Environ. Entomol. 28: 456 460.

2001. Bentz, J., and Sherald, J. 2001. Transmission of the xylem-limited bacterium Xylella fastidiosa to shade trees by insect vectors. Proceedings of the APS Wilt Diseases of Shade Trees: National Conference, MN. pp. 203-208.

2001. Bentz, J., and Townsend, A. M.. Leaf element content and utilization of maple and elm as hosts by the potato leafhopper (Homoptera: Cicadellidae). Environ. Entomol. 30(3): 533-539.

2002. Griesbach, R.J.,. Neal, J.W, Jr., and Bentz, J. Arthropod resistance in a Petunia ecotype with glabrous leaves. HortScience 37: 383-385.

2003. Bentz, J., Huang, Q., Jordan, R. Bacterial leaf scorch in shade trees. Available from: http://www.usna.usda.gov/Research/BacterialLeafScorch.html.

2003. Bentz, J. Shading induced variability in azalea mediates its suitability as a host for the azalea lace bug. Journal of the American Society for Horticultural Science. 128: 497-503.

2003. Bentz, J., and A. M. Townsend. Nitrogen fertilization and use of container-grown maple selections as hosts by the potato leafhopper. Journal of the American Society for Horticultural Science. 128(6): 821-826.

2004. Roh, M. S.; J. Bentz, P. Wang, L. Ercheng; and M. Koshioka. Maturity and temperature stratification affect the germination of Styrax japonicus seeds. Journal of Horticultural Science & Biotechnology. 79(4): 645-651.

2004. Bentz, J., and A. M. Townsend. Spatial and temporal patterns of abundance of the potato leafhopper among red maples. Annals of Applied Biology. 145(2):157-164.

2004. Bentz, J., and A. M. Townsend. Diversity and abundance of leafhopper species (Homoptera: Cicadellidae) among red maple clones. Journal of Insect Conservation. (In Press).

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