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 pets 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 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.
3. Progress Report:
Progress was made on all three objectives of the Project Plant Outline issued January 2011, all of which fall under National Program 304 Crop Protection and Quarantine, Component II, Problem Areas IIA and IIB. Under Objective 1, we discovered that psyllids are preferentially attracted to potato plants that are recently infected with the causal agent of zebra chip disease. Preliminary determinations were made of the time required for the Liberibacter pathogen of zebra chip to be taken up by psyllids and transmission to potato, which is about 2 weeks. It was determined that as few as one infected psyllid can transmit the Liberibacter pathogen to a potato plant, and the same for transmission of the BLTVA phytoplasma from the beet leafhopper to a potato plant. Field trials showed that all major potato varieties grown in the western U.S. are susceptible to zebra chip disease. Solvent extracts of male and female potato psyllids were compared to determine additional female specific compounds that may have pheromonal activity. Preliminary field trials of a putative sex pheromone of potato psyllid were conducted but did not show significant attraction of males. In collaboration with ARS Prosser and Oregon State University, zebra chip disease of potato, and Liberibacter infection of potato psyllid, were documented for the first time in the Pacific Northwest. Novel floral-based chemical lures were field-tested and shown to be attractive to the moth of the spotted cutworm, which defoliates potato plants in Washington. Under Objective 2, a feeding attractant that is based on floral chemicals and developed for European species of wireworms was field tested for trapping Limonius wireworms in the Pacific Northwest, with no indication of attraction. Under Objective 3, we conducted laboratory assays to determine effects of a set of chemicals and plant essential oils on wireworm feeding on a bait. A sugar, a protein, and two of the plant oils increased wireworm consumption of bait, which provides the possibility of improving the bait efficacy in a lure and kill formulation. We determined that potato tubers from zebra chip-infected plants develop symptoms in storage, and that tubers expressing zebra chip disease do not contribute to the spread of the disease, because they do not sprout. Screening of potato breeding lines showed some level of resistance to zebra chip disease.
1. Discovery of Zebra Chip Disease in Pacific Northwest Potatoes. Zebra chip, a new and economically important insect-vectored disease of potato, had so far been limited to the southwest and central U.S. since its initial appearance in Texas in 2000. In collaboration with other ARS and university scientists, researchers at USDA-ARS Wapato in WA identified and reported for the first time zebra chip and its pathogen in the Columbia Basin of Washington and Oregon commercial potato fields in September 2011. It was also determined that potato psyllids carrying the zebra chip pathogen in the Columbia Basin likely originated from southern California and/or northwest Mexico. This information is helping growers in the Pacific Northwest develop strategies to effectively control the psyllid vector to minimize damage caused by zebra chip in this major potato growing region of U.S.
2. Zebra chip pathogen incubation period in its insect vector determined. Little is known on the epidemiology of zebra chip, an economically important disease of potato in U.S. that is caused by a previously undescribed species of the bacterium liberibacter hosted by the potato psyllid. Researchers at USDA-ARS Wapato in Washington determined the time that elapses from initial acquisition of the bacterium by the psyllid to the ability of this insect to transmit it to potato plants and cause the disease. It was discovered that this incubation period for the bacterium in the psyllid vector is about two weeks. Information from this research will help potato growers to target the potato psyllid in a timely manner. This will facilitate control before this insect vector is capable of transmitting the zebra chip pathogen and causing damage to potato crops.
Munyaneza, J.E., Lemmetty, A., Nissinen, A.I., Sengoda, V.G., Fisher, T.W. 2011. Molecular detection of aster yellows phytoplasma and 'Candidatus Liberibacter solanacearum' in carrots affected by the psyllid Trioza apicalis (Hemiptera: triozidae) in Finland. European Journal of Plant Pathology. 93(3):697-700.