OLSON YELLOW STICKY TRAP - DECISION-MAKING TOOL FOR SAMPLING WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) ADULTS IN-FIELD CORN

Field studies were conducted in Virginia in 1992-1994 to evaluate the effectiveness of using counts of western corn rootworm, Diabrotica vir gifera virgifera LeConte, adults on Olson yellow sticky traps and in t he ear-zone region of corn plants to predict subsequent root-feeding d amage in corn. Western corn rootworm adults accounted for >97% of the total corn rootworm species sampled. Adult population estimates obtain ed at calendar week 33 (mid-August) had the highest correlations with subsequent root damage among all sampling intervals from July to Augus t for both the Olson sticky trap and the ear-zone visual counts. Linea r regression models for Olson sticky trap and ear-zone counts explaine d 65 and 41% of the variability in root ratings, respectively, and wer e used to calculate western corn rootworm economic thresholds for each sampling method. Various edaphic and agronomic variables, including p lanting date, years in continuous corn, percentage of sand in soil, an d monthly precipitation levels were used to help improve the models of adult counts as a predictor of subsequent damage. Sampling plans and economic thresholds of 20 western corn rootworm adults per trap per we ek for the Olson sticky trap and 0.35 adults per ear zone were suggest ed. Olson sticky traps correctly predicted economic damage (root ratin g >3.5) to corn in 81% of the fields, and resulted in only one serious error of failing to predict economic damage. Ear-zone counts correctl y predicted economic damage to corn in 74% of the fields but resulted in 6 (14%) serious prediction errors.