2013 Annual Report
Insect pests of potato and tree fruits are a serious threat to the potato and fruit industry. Collaborative research between ARS and Washington State University assessed the biology and ecology of insect pests of potatoes and tree fruits, in addition to developing effective monitoring program and management tools for these pests. Three graduate students described the biology and ecology of the potato psyllid and beet leafhopper, insect vectors of zebra chip and purple top diseases, respectively. These two emerging diseases of potato have caused millions of dollars in losses to the U.S. potato industry and zebra chip was recently reported in the Pacific Northwest, where over 50% of U.S. potatoes are produced. An ‘Electrical Penetration Graph (EPG)’ was used to analyze feeding by the potato psyllid. These results described salivation and ingestion which were identified and characterized. These feeding behaviors are useful to directly assess whether the potato psyllid is acquiring and transmitting Liberibacter and to determine feeding duration. It was discovered that psyllid adults were more efficient in transmitting the bacterium to potato than their immature stages. It was determined that a single potato psyllid can effectively transmit liberibacter to potato in a period as short as six hours and was as damaging as 25 psyllids per plant, causing substantial potato yield loss and reduction in tuber processing quality. It was discovered that transmission of the zebra chip pathogen by the potato psyllid was negatively affected by temperatures at 90 °F and above. It was demonstrated that local movement of the beet leafhopper from weeds to nearby potato fields can be traced by marking the insects with egg and milk protein markers.
For three field seasons, ca twenty commercial potato fields were sampled each week through the growing season, using a beat sheet at 10 sites from the field edge towards the center. Caterpillars collected were reared to the adult stage for identification. For two of those years,l arvae that died were identified by analysis of the nucleotide sequence of the COI mitochondrial gene and comparing it to an online data base for North American moths. Three species, spotted cutworm, cabbage looper, and bertha armyworm, consistently comprised the majority of the caterpillars found on potato.
A set of six potato varieties were evaluated in a laboratory assay as food for larvae of spotted and clover cutworms, yellow striped and bertha armyworms, cabbage, alfalfa, and celery loopers, and Lacanobia subjuncta. The study yielded the percent survival from egg hatch to adult, pupal weights, and development rate. Generally, cabbage looper, western yellowstriped armyworm, Lacanobia subjuncta, and spotted cutworm did well to develop fully on all potato varieties, while alfalfa looper, celery looper, and clover cutworm did poorly with high mortality of larvae. Bertha armyworm was intermediate. When comparing potato varieties, there was some indication of susceptibility of Norkotah potato.
The volatile chemicals from immature and mature apple fruit were evaluated to determine the electroantennal responses of the codling moth. This work showed that the moth antennae are particularly sensitive to a set of 4 apple aroma compounds. This work suggests apple compounds that might be involved in the finding and selecting of oviposition sites by female codling moths. Information from this research will lead to development of effective management strategies for important insect pests of potato.