Report Information
Participants
William Bowers - U. Arizona;
Gary Felton - Pennsylvania State University;
Michael Haverty - USDA Forest Service, Berkeley, CA;
Jocelyn Millar - U. California, Riverside;
Marion Page - USDA Forest Service, Berkeley, CA;
Ron Pardini - U. Nevada, Reno;
David Schooley - U. Nevada, Reno;
Steve Seybold - U. Minnesota;
Claus Tittiger - U. Nevada, Reno;
David Weaver - Montana State University
William Welch - U. Nevada, Reno
Brief Summary of Minutes
Accomplishments
The past year saw significant progress in the three objectives of the W-189 regional project, both at basic and applied research levels. Most progress and collaborative efforts were found in Objective 1, though significant progress was made in all objective. Some of the progress doesnt neatly fit any particular objective, yet is still useful and germane to biorational methods of insect pest management. Those projects are summarized with others in Objective to which they are most closely related. Specific progress is briefly outlined for each Objective below.<br />
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<br>Objective 1: To determine the chemistry, biology, biochemistry, physiology, and the neurophysiological mechanisms of perception of specific semiochemicals potentially useful for control of pest insects, and to study semiochemicals in model insect systems for later application to target pest insects. <br />
<br> Collaborative efforts among M. Haverty, L. Nelson, and M. Page (USDA Forest Service, Berkeley) lead to ground breaking discoveries on the population structures of Reticulotermes termites. Studies of cuticular hydrocarbon profiles revealed 26 distinct chemical phenotypes across North America that grouped into three distinct lineages or clades, suggesting what had been thought to be a single species may in fact be three different species. Similarly, hydrocarbon profiles segregate with swarming flight times for populations in northern and southern California, suggesting reproductive isolation and distinct taxa. This knowledge has facilitated the study of the foraging ecology of subterranean termites in California, which has, in turn, helped to understand the difficulties of using wooden baits for termite control. We now know that houses can be infested by numerous termite colonies made up of different species, instead of just one species. This information is integral in developing new strategies to bait and control these pests.<br />
<br> Related studies on termite preferences for different types of wood by L. Bjostads group (Colorado St. U.) has resulted in patent application by the Colorado St. University Research Foundation Tech. concerning feeding stimulants found in wood.<br />
<br> Various flea beetles (Phyllotreta and Aphthona spp.) are serious pests of canola crops and rangeland flora. While it was known that males release a pheromone, the various components were unknown. Collaborative efforts of R. Bartelt and A. Cossi (USDA-ARS-NCAUR, Peoria, IL) have revealed the structures of seven sesquiterpenes, all found in each of the species they studied, yet some of which are novel or rare in nature. These preliminary results are the first step to understanding the pheromone composition of flea beetles and the future development of semiochemical-based control strategies.<br />
<br> Similarly, Cossi and Bartelt have made preliminary identification of a female-specific volatile and likely pheromone component [(Z)-9-octadecen-4-olide] from the currant stem girdler (Janus integer). Since this serious pest of red currant, poplar and willow trees appears unaffected by current pesticide applications, an understanding of their chemical ecology may lead to more effective control practices.<br />
<br> D. Weaver (Montana St. U.) is continuing to characterize wheat sawfly (Cephus cinctus) pheromone components in collaboration with A. Cossi and R. Bartelt (USDA-ARS-NCAUR, IL) in order to understand chemical communication in this notable wheat pest. Field studies showed that light, in addition to semiochemicals, has an effect on behavior, implying that the insects may have evolved a system of leks for breeding. Additional work has led to an increased understanding of host plant compound composition and feeding preferences: the wheat sawfly develops in cultivated wheat, but not in wild oats, even though females will lay eggs in both plants (see Objective 2, below). New control strategies using the concept of toxic buffer zones to protect crops are likely to be developed using this information.<br />
<br> Communication among agriculturally important stink bugs (Thyanta, Chlorochroa, and Acrosternum spp.) also involves two components. While a long-range pheromone was identified and used to improve trap designs, this past year saw the discovery that the insects use species-specific substrate-borne vibrational signals for short range attraction (J. Millar and workers, U. California, Riverside). This has crucial implications for the design of traps and methods for monitoring stink bug populations. J. Millars group also identified the sex pheromone of the vine mealy bug, a worldwide pest of grapes that has recently invaded California, and will have a commercial trap using the pheromone available to growers by Spring 2002. The trap will be used initially to monitor the spread of populations, with efforts to use the information for more direct control in progress. Similarly, the grape leaf folder sex pheromone was also identified by Millar, in collaboration with R. Bartelt (USDA, IL). A monitoring system based on this pheromone is scheduled to be available to vineyards by Spring 2002. <br />
<br> New monitoring systems for sap beetles (Colopterus truncatus) can now be developed due to work by Seybolds group (U. Minnesota) in collaboration with R. Bartelt (USDA-ARS) involving compounds that can cheaply and efficiently attract these oak wilt disease vectors to traps. A pheromone-based monitoring system will be useful for land managers to monitor beetle activity and time pruning to avoid peak beetle flight periods. Further work has also determined that wood chips themselves are not attractive to the beetles, thus correcting the misconception that wood chips near an uninfected tree may pose the risk of attracting oak wilt vectors.<br />
<br> Continuing efforts by Blomquist and Tittiger (U. Nevada, Reno) to understand the regulation and biosynthesis of monoterpenoid pheromone components in pine bark beetles have yielded a putative cDNA clone for a geranyl diphosphate synthase (GPPS). Computer modeling (in collaboration with W. Welch, U. Nevada, Reno) confirms that the putative GPPS is structurally similar to other isoprenyl diphosphate synthases, but with some minor, though potentially important, differences. Since most animals, with the exception of a few pest bark beetles, do not have this enzyme activity, disrupting GPPS would be a highly specific method of pest control. Similar research on the cotton boll weevil, one of Americas most economically important agricultural pests, indicates that those insects may not use the same regulatory and biosynthetic mechanisms as the bark beetles, even though their pheromone components are chemically similar.<br />
<br> Tittigers group is establishing an expressed sequence tag (EST) database of active genes in pheromone producing bark beetle (Ips pini) tissue, with nearly 700 clones identified so far. This resource will be extremely useful to identify and isolate pheromone biosynthetic enzymes as well as components of the juvenile hormone regulatory apparatus. The mechanism by which juvenile hormone affects gene expression is one of entomologys long standing mysteries. The combination of a genomics-based approach, a strongly responding tissue, and a readily identifiable metabolic pathway, should yield advances that will be broadly applicable to all insects.<br />
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<br>Objective 2: To discover, identify, and determine the physiological mode of action of plant metabolites toxic to insects, for development into biorational pesticides.<br />
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<br> D. Weavers group (Montana State U.) observation that stem saw fly eggs laid in wild oats do not develop suggests those plants contain an inhibitory compound or toxin that, when identified, would have promising uses for pest control.<br />
<br> Some plants can be induced to produce photoecdystyeroids in response to different stresses, and these chemicals have been shown by W. Bowerss group (U. Arizona) to inhibit insect and nematode development. Further work by this group shows that induction of the photoecdysteroids in spinach and sugar beet is localized to the root, resulting in protection of the plant from herbivorous insects and nematodes. These studies suggest that inducing plants to produce these chemicals could be a viable method of pest control, and the responses of insects to the chemicals may allow the development of simple diagnostic tests for photoecdysteroid induction. Such a tool would be useful at a basic research level in studies of signaling pathways that regulate this phenomenon in plants.<br />
<br> Ryanodine is a natural plant chemical that inhibits the ryanodime receptor (RyR) - a calcium channel protein that has important roles in cell signaling. Since insect RyR is strongly sensitive to ryanodine, while mammalian RyR is not, ryanodine is a very strong candidate as a highly specific pesticide. B. Welch (U. Nevada, Reno) has been pursuing physical chemical and molecular modeling studies of RyR and its various ligands. Studies of how ryanodine and various nucleotides alter the structure of the receptor and its function through binding provide important leads regarding binding sites and their potential roles as targets for natural products in pest control.<br />
<br> While toxic plant chemicals have the greatest potential as pesticides, other plant chemicals that may affect insect behavior have potential uses, and thus also deserve attention. Work on these areas includes the recent filing of a patent regarding stimulants found in wood that affect termite feeding (L. Bjostads group, Colardo State U.), and the discovery by Seybolds group (U. Minnesota) that oak volatiles are not significantly attractive to nitidulid vectors of oak wilt disease. These are data that, while not necessarily leading to new insecticides, are useful to pest controllers, land managers and forest health professionals.<br />
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<br>Objective 3: To develop peptides and proteins as novel agents for plant protection, and increase our understanding of the roles that peptides and proteins can play in pest control. <br />
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<br> Schooley (U. Nevada, Reno), in continuing his work on insect diuretic and antidiuretic peptide hormones, has discovered novel peptides from two significant pests: the tobacco horn worm (Manduca sexta) and the common meal worm (Tenebrio molitor). Two antidiuretic peptides from Tenebrio molitor are currently being characterized, one of which is effective at extremely low doses. Disruption of the activity of any of these peptides, with the resulting loss of control of diuresis, would be a highly specific method of pest control.<br />
<br> The saliva of the cotton boll worm, Helicoverpa zea can inhibit natural plant responses to predation. Gary Feltons group (Pennsylvania State) has characterized various glucose oxidase genes expressed in larvae and studied their effects on plant defenses. Because the enzymes effect different aspects of the plant defense system, this exciting preliminary work is leading to further studies of how expressing these genes in plants may trigger disease resistance and tolerance to adverse abiotic conditions, with the long term benefit being the development of more robust crops.<br />
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