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Sensory-Based Action Threshold for Multicolored Asian Lady Beetle-Related Taint in Winegrapes

¹ Graduate student, ² Senior scientist, ³ Professor, Department of Entomology, 219 Hodson Hall, 1980 Folwell Avenue, University of Minnesota, Saint Paul, MN 55108; ⁴ Professor, ⁵ Graduate student, Department of Food Science and Nutrition, 1334 Eckles Avenue, University of Minnesota, Saint Paul, MN 55108; and ⁶ Senior scientist, Horticulture Research Center, 600 Arboretum Blvd, Excelsior, MN 55331.

^* Corresponding author (email: galva008{at}umn.edu; tel: 612 624-3670; fax: 612 625-5299)

Action thresholds were developed for the Frontenac winegrape to aid growers in the management of the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Sensory thresholds were determined for the H. axyridis-related taint in winegrapes by artificial infestation of H. axyridis-free grapes with live adult beetles. In a series of three-alternative forced choice (3-AFC) tests, a tasting panel compared control wine prepared with H. axyridis-free grapes and wine produced with increasing insect levels. Logistic regression was used to relate the number of H. axyridis per kg of grapes to the proportion of correct 3-AFC tests. With the same logistic regression model, the probability of correct answers was estimated using the logit probability function. The same logistic model was also used to estimate the infestation level for a given probability of correct answers. The estimated threshold at which 10% of the population could detect the characteristic off-flavor of H. axyridis was 1.9 beetle/kg grape, or 0.27 beetle/grape cluster of Frontenac. The sensory thresholds presented here can be interpreted as action thresholds for H. axyridis in winegrapes (i.e., number of H. axyridis per kg of grapes). These new action thresholds add information in the management of the H. axyridis in grapes, which when combined with existing control methods and sampling plans, form the basis of integrated pest management for this insect in winegrapes.

Key words: Harmonia axyridis, tasting panel, winegrapes, contaminant pest