California Agricultural Research Priorities Pierce's Disease (2004) / Chapter Skim
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3 Host-Vector Interaction
3 Host-Vector Interaction
Pages 55-87
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From page 55... ...
Ecologically based pest management (EBPM) is "the release of living predatory, parasitic, pathogenic, or antagonistic organisms (biological control organisms)
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From page 56... ...
· traditional biological control (classical, augmentation, conservation) · sterile male technique · mass trapping using a compound derived from a living organism · direct use of chemical agents (synthetic toxins, biorational insecticides, behavior-modifying chemicals, insect growth regulators)
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From page 57... ...
Although constant searches for new plant material or germplasm could remain part of this process, common sense suggests that understanding the plant traits that do or can confer resistance would greatly accelerate HPR development. Successful HPR use in EBPM requires a detailed understanding of how the pest exploits the plant and how plant traits interfere with pests.
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From page 58... ...
Insect diets range from extremely narrow (limited to a particular tissue on a particular plant species) to very broad (feeding successfully on many plant species from several plant families)
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From page 59... ...
. It is generally easier to understand insect adaptation to plants and the reasons for using particular plant species on the basis of chemistry than it is to explain the adaptation on the basis of adjustment to the physical traits of the host plant.
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From page 60... ...
Because insect adaptation to host plants is continuous, uniform populations of crop plants that express the same resistance traits favor the rapid evolution of insects to overcome those traits. For this reason, and because ecosystem complexity itself interferes with finding and exploiting host plants, the simplification inherent to modern agriculture also contributes to the development of insect pest problems.
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From page 61... ...
The insect's association with a plant species could mean that it feeds there, reproduces there, or both. There are examples of both types of association with various host plants, but the committee does not have a comprehensive picture of the associations between any of the Xf-transmitting sharpshooters and the host plant communities in their habitats.
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From page 62... ...
and that various plant species exhibit genotypic resistance to xylem-feeding and other leafhoppers (Elden and Lambert, 1992; Kornegay et al., 1989; Martinson and Dennehy, 1995; Sanford et al., 1990; Tingey and Laubengayer, 1981) suggest that plant traits do influence sharpshooter attack.
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From page 63... ...
A library of phenotypic and genetic resistance traits is needed for effective use of HPR, but few resistance traits have been identified because too little is known about how the insects and plants interact. Although each of the Xf-transmitting sharpshooter species can be found on and could feed on a large number of plant species, the insects' preferences for those plants and the suitability of various plants and plant tissues for insect performance have not been determined.
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From page 64... ...
Host plant resistance should be emphasized as a component of ecologically based insect management strategies in the grapevinesharpshooterXf system. Methods for manipulating grapevine resistance should be developed for experimental use to identify key resistance traits and with an eye toward eventual deployment.
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From page 65... ...
Although the predicted effects of plant diversity on insect herbivores with narrow host ranges are reasonably straightforward, predictions for herbivores with broad host ranges are less clear. The determining factors for insect response are the distribution of host and nonhost plants in the system and the preferences of the herbivore.
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From page 66... ...
. The use of cover crops or ground covers in orchards and vineyards can help reduce leafhopper populations (Costello and Daane, 2003; Daane and Costello, 1998; Hanna et al., 2003; Roltsch et al., 1998)
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From page 67... ...
Detailed, quantitative studies should examine leafhopper performance (survivorship, fecundity, development time) on and preference for a broad range of potential ground cover crops (Category 2)
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From page 68... ...
. In northern California, the removal of host plants of the bluegreen sharpshooter in riparian vegetation bordering vineyards can reduce leafhopper populations (A.
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From page 69... ...
showed that the spatiotemporal pattern of host availability in the landscape can influence the epidemiology of the leafhopper-transmitted rice tungro virus. The success in reducing abundance of highly mobile, polyphagous leafhoppers through the management of host and nonhost plants suggests that the densities of sharpshooters can also be affected by vegetation management.
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From page 70... ...
Detailed, quantitative studies should examine leafhopper preference for potential host plants in the context of natural assemblages of hosts in the field. Studies of leafhopper performance on a broad range of potential host plants are essential to elucidate host ranges (Category 2)
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From page 71... ...
The economic feasibility of conservation or augmentation biological control is likely to depend on the development of economical, efficient, and effective augmentation strategies or conservation tactics. Leafhopper abundance is regulated by a variety of natural enemies (J.
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From page 72... ...
Biological Control and Pest Abundance A major constraint on EBPM of GWSS is its function as a vector of PD. The use of biological control of any pest species with parasitoids, predators, pathogens, or another EBPM tactic, is more problematic when the targeted pest being is a vector (Mahr and Ridgway, 1993)
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From page 73... ...
Clearly, any recommendation for the use of biological control as a means of controlling pest populations or even reducing pest populations requires further research into interactions between GWSS and its natural enemies. Recommendation 3.11.
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From page 74... ...
. Economic Feasibility of Biological Control The determination of whether control exerted by natural enemies is sufficient and economically feasible should be made within the context of economic thresholds.
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From page 75... ...
. "The economic feasibility of any given biological control strategy is unique, and depends on and will vary with the independent and interactive effects of the ecological and economic characteristics of the crop-pest system considered" (Reichelderfer, 1981)
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From page 76... ...
Some of the constraints on the use of biological control are the limitations of the organisms themselves or of the environments in which they must exist. Introduced species, if successful, will establish viable populations but could fail to do so at the densities needed for effective pest management.
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From page 77... ...
Environmental Impact of Biological Control Many of the consequences of EBPM are unknown. The use of introduced natural enemies, sterile insects, microbial pesticides, and pheromones has sometimes directly or indirectly affected not only the targeted pest species but nontarget plants or other insects.
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From page 78... ...
OTHER OPTIONS The recommended incorporation of some tactics and approaches into an EBPM scheme does not mean that other tactics will not be shown to be effective as more research is done. However, available information on leafhoppers in general and on GWSS and its host plants in particular, suggests that the potential of some approaches to the management of the PDGWSS is highly questionable.
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From page 79... ...
Research results for biotrational insecticides indicate acceptable control provided by sugar esters and possibly by insecticidal soaps. This is a recent area of research and additional studies would be useful to more clearly develop the application process for such materials.
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From page 80... ...
The approach works only if the females mate once, if the released males are competitive with feral males, and if the number of released males at least matches that of feral males. The use of the sterile male technique has been applied against few pest species, in part because of the technique's biological and ecological requirements.
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From page 81... ...
. Foliar application of systemics can be done by aircraft, by air blast sprayers or by hydraulic sprayers.
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From page 82... ...
. Nonsystemic insecticides are commonly applied by air blast sprayers.
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From page 83... ...
The most effective use of nonsystemic insecticides therefore would be as a rapid response to an invasion of GWSS from adjacent host plants. Most of those chemicals have exposure limits for field workers and dissipation times before human consumption.
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From page 84... ...
Applying a coating of finely divided kaolin clay has been found to effectively repel both GWSS nymphs and adults. However, the mechanism for this response is poorly understood and the indirect effects (e.g., the impacts on beneficial insects)
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From page 85... ...
reported a peak in adult GWSS trap catches in July. If GWSS primarily overwinters as adults, and there appears to be a small population peak in February and March, it would be efficient to schedule a control application with the emergence of the adults at the location of first egg laying on neighboring host plants, such as gardenia and citrus.
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From page 86... ...
Many pesticides are applied by air blast sprayers, at 80100 gal/acre at velocities up to 60 mph. Drift can be measured as far as 100 yd away after spraying through a tree canopy in relatively calm wind (Derksen et al., 2000 Fox et al., 1994)
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From page 87... ...
Recommendation 3.17. Research should assess the economic feasibility of specific chemical control strategies and develop decision and cost models to guide growers in setting up chemical control methods for GWSS (Category1)
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