2009 Annual Report
1a.Objectives (from AD-416)
Objective 1: Develop new knowledge of behavior, genetics, physiology, and ecology of wireworms, aphids, secondary potato pests, and their natural enemies, that provides opportunities for new and improved biorational control of potato insect pests.
Objective 2: Develop monitoring methods and techniques that reduce grower risk from wireworms that improve predictability of threats to potatoes.
Objective 3: Develop economical, sustainable, and ecologically sound methods for control of aphids, wireworms, and secondary pests of potatoes.
1b.Approach (from AD-416)
Objective 1.The seasonal phenology and movement of green peach aphid and leafhoppers in potato will be described quantitatively. Effects of induced defenses of potato on behavior, development, and reproduction by insect pests will be determined. Microbial flora resident in the midgut of wireworm larvae will be genetically altered (paratransgenesis) to produce physiological or toxic conditions that in turn will be detrimental to the survival of the wireworm. The role and concentrations of carbon dioxide as an attractant for Pacific coast wireworm and will be determined. Mating behavior of Limonius canus (Pacific coast wireworm) will be described.
Objective 2. Baiting methods to monitor wireworms in potatoes will be developed, and the feasibility of using baits to predict end-of-season damage to tubers will be determined. The seasonal phenology of wireworm damage to tubers will be described to assist in management decisions.
Objective 3. The effectiveness of transgenic and traditionally bred potato varieties for resistance to wireworms and secondary pests will be demonstrated. Methods to manage wireworms and potato flea beetle in potatoes using entomopathogens will be developed. Methods for enhancing biological control of green peach aphid will be improved, including use of habitat modification, selective insecticides, and predator attractants. Action thresholds for leafhoppers that vector phytoplasmas will be estimated. Extent of insecticide resistance in green peach aphid in the Northwest will be determined. Formerly 5352-22000-014-00D (3/05).
The phenology of the beet leafhopper was determined and the seasonal incidence of BLTVA phytoplasma was determined in the beet leafhopper. Younger potato plants were found to be more susceptibility to purple top disease. Field experiments evaluated insecticides and mineral oils for controlling the green peach aphid, the vector of potato virus Y (PVY) and potato leafroll virus (PLRV). Field and laboratory experiments at USDA-ARS Weslaco (TX), Wapato and Prosser (WA) demonstrated that zebra chip, a new and damaging potato disease in southwestern United States, Mexico, Central America, and New Zealand, is associated with the potato psyllid and the bacterium “Candidatus Liberibacter solanacearum”. This bacterium was associated with zebra chip and other important diseases of tomatoes and peppers in Mexico. Also, the potato psyllid was found to occur in the state of Washington. A series of transmission studies at USDA-ARS Wapato and Prosser assessed the acquisition and inoculation access periods required for the potato psyllid to effectively transmit the zebra chip pathogen liberibacter. Four hours or less were enough for the potato psyllid to inoculate the bacterium into healthy plants. In addition, phenotypic and etiological differences between zebra chip and potato psyllid yellows were described. It was demonstrated that zebra chip was associated with the bacterium liberibacter, whereas the psyllid yellows disease of potato is not. In collaboration with other scientists and the potato industry, USDA-ARS Wapato researchers develop the use of selective insecticides and cultural practices for the management of the potato psyllid to reduce zebra chip in potatoes. As a result, growers in the Lower Rio Grande Valley of Texas, one of the regions seriously affected by the disease, keep zebra chip incidence under manageable levels by applying insecticides targeted against the potato psyllid.
The incidence and species makeup of caterpillars in potato fields was determined. The comparative susceptibility of 6 potato varieties to several cutworms, loopers, and armyworms was determined. A new feeding attractant was identified from butterfly bush flowers and field tested against the alfalfa looper moth. Pheromone lures were used to determine the geographic distribution and relative abundance of potato tuberworm in eastern Washington and adjacent Oregon. Preliminary assays in an olfactometer demonstrated sex attraction by male potato psylla. The response of wild bees to floral lures used for moths was assessed, with the aim of minimizing capture of these non-target beneficial insects. An experimental bait for use in attract-and-kill of wireworm pests in potatoes was tested in laboratory and field trials.
Baits for Wireworm Control. Difficulties in controlling and monitoring wireworms in potatoes have led to efforts at developing a synthetic attractant. First generation baits obtained from industry were found by ARS scientists at Wapato, WA to attract wireworms in laboratory assays, and attractiveness of baits was shown to depend upon the rate that the bait emitted carbon dioxide. Baits with insecticide added were found to attract and kill wireworms, and to provide tuber protection in the field. Research completed here will allow progress towards commercial production of a bait having attract-and-kill properties.
Control of Potato Tuberworm (PTW) with a Specific Granulovirus. Potato tuber worm has become a pest of potato in the Lower Columbia Basin of Oregon and Washington. A virus that kills potato tuber worm is being developed for control of the pest in stored potatoes and in fields of potatoes. ARS scientists in Wapato, WA conducted field trials of applications of virus to potato crops and found that light populations of PTW were significantly suppressed while a variety of non-target insects, including predators and parasitoids of crop pests, were unaffected. Stored potato tubers were treated by submersion in an aqueous suspension of virus and after 3 months of storage, the virus substantially reduced entries of PTW into tubers and killed a high percentage of larvae within pre-infested tubers. Formulations of the virus hold promise as a non-chemical means of controlling potato tuber worm under some conditions.
Control of Wireworm with Pathogen-inoculated Baits. Control methods are needed to protect potato tubers from infestations of wireworms in the field. ARS scientists at Wapota, WA incorporated the insect-specific fungus, Metarhizium anisopliae, into an oat meal bait that attracts wireworms. The baits with fungus were 4 times as attractive compared with the oatmeal baits alone. Also, live wireworms collected from the baits became infected with the fungus thereby providing other sources of inoculum to spread the pathogen. The pathogen is fatal to the wireworm larvae, thus providing control of wireworms attracted to the bait. It is envisioned that the bait containing fungus could draw larvae away from potato tubers and kill the wireworms in the process, thus providing a potential means to control this pest.
Susceptibility of Potato to Purple Top Disease in the Columbia Basin. Our knowledge of the impact of purple top disease on potato in the Pacific Northwest is incomplete. There are significant differences in susceptibility of potato varieties to purple top. ARS scientists in Wapato, WA found that potato plants of younger growth stages were more susceptible to the disease than older ones. In addition, we found the incidence of purple top disease in potatoes could substantially be reduced by effectively and appropriately protecting susceptible potato varieties and plant growth stages against the beet leafhopper, the purple top insect vector. Information from this study will help potato growers affected by purple top disease in the Columbia Basin reduce damage caused by this potato disease through selection of potato cultivars that are resistant to, or tolerant of, the disease. Furthermore, protecting specific varieties and plant growth stages against the beet leafhopper could lead to substantial reduction of insecticide applications targeted against this insect pest.
Causal Agent of Zebra Chip Potato Disease in Mexico Identified. Zebra chip, a new and emerging potato disease, is causing millions of dollars in losses to potato producers and processors in the southwestern of the United States, Mexico, Central America, and New Zealand. Until recently, the disease causal agent and vector were unknown. It was shown that zebra chip is associated with the potato/tomato psyllid. Although the disease has been associated with the bacterium “Candidatus Liberibacter solanacearum” in the United States and New Zealand, the causal agent of the disease in Mexico and Central America had not been previously verified. ARS researchers in Wapato, WA reported the association of this new bacterium with zebra chip of potato and other important diseases of tomatoes and peppers in Mexico. Information from this research will allow growers in Mexico to reduce damage caused by zebra chip and other related vegetable diseases by focusing on potato psyllid monitoring and timely insecticide applications targeted against this insect pest.
Alfalfa Looper Feeding Attractant from Butterfly Bush Flowers. Numerous vegetable crops, including potato, are attacked by several polyphagous species of loopers, including the alfalfa looper, cabbage looper, soybean looper, and celery looper. New pest control methods are needed to replace restricted pesticides. ARS researchers at the USDA, ARS Yakima Agricultural Research Laboratory, Wapato, WA identified the odor compounds of butterfly bush flowers to isolate chemicals that are attractive to pest moths. One of the butterfly bush flower odor compounds was GC-EAD active and was subsequently found in field trials to be very attractive to alfalfa looper moths. In addition, this chemical was also strongly co-attractive with an attractive compound previously isolated from flowers of Oregongrape shrubs. These combinations of chemicals may be used in attract-and-kill or mass trapping strategies to control loopers in vegetable crops with a greatly reduced use of pesticide.
Transmission Mechanisms of Zebra Chip Potato Disease Elucidated. It has recently been determined that zebra chip is caused by the bacterium “Candidatus Liberibacter solanacearum” transmitted by the potato psyllid. However, transmission mechanisms of this pathogen by the psyllid to potato are not well understood. Transmission studies conducted by ARS scientists at Wapato and Prosser, WA, assessed the acquisition and inoculation access periods required for the potato psyllid to effectively transmit the bacterium liberibacter. Results indicated that the potato psyllid is able to effectively acquire this pathogen in one hour or less. Also, results show that four hours or less are enough for this insect to successfully inoculate the bacterium to healthy plants. Information from this research will increase our understanding of how zebra chip and other related diseases are transmitted that will lead to the development of effective management strategies for these important diseases.
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Unruh, T.R., Willett, L.S. 2008. Survey for Resistance to Four Inecticides in Myzus persicae Clones from Peach and Weeds in South-central Washington. Journal of Economic Entomology 101:1919-1929.
Arthurs, S.P., Lacey, L.A., Pruneda, J.N., Rondon, S. 2008. Semi-field evaluation of the potato tuber moth, phthorimaea operculella zeller, granulovirus and bacillus thuringiensis var. kurstaki for season-long control of p. operculella. Entomologia Experimentalis et Applicata 129:276-285.
Arthurs, S.P., Lacey, L.A., De La Rosa, F.L. 2008. Evaluation of a Granulovirus (PoGV) and Bacillus Thuringiensis subsp. kurstaki for Control of the Potato Tuberworm in Stored Tubers. Journal of Economic Entomology 101:1540-1546.
Ramirez II, R., Henderson, D.R., Riga, K., Lacey, L.A., Snyder, W.E. 2008. Harmful Effects of Mustard Bio-fumigants on Entomopathogenic Nematodes. Biological Control 48:147.154.
Munyaneza, J.E., Buchman, J.L., Upton, J.E., Goolsby, J., Crosslin, J., Bester, G., Miles, G.P., Sengoda, V.G. 2008. Impact of Different Potato Psyllid Populations on Zebra Chip Disease Incidence, Severity, and Potato Yield. Subtropical Plant Science 60:27-37.
Lacey, L.A., Kroschel, J. 2009. Microbial Control of the Potato Tuber Moth (Lepidoptera: Gelechiidae). Fruit, Vegetable, and Cereal Science and Biotechnology 3:46-54.
Guedot, C.N., Landolt, P.J., Smithhisler, C. 2008. Odorants of the Flowers of Butterfly Bush, Buddleia davidii as Possible Attractants of Pest Species of Moths. Florida Entomologist 91(4):576-582.
Meagher Jr, R.L., Landolt, P.J. 2008. Attractiveness of binary blends of floral odorant compounds to moths in Florida, USA. Entomologia Experimentalis et Applicata. 128(2):323-329.