(Academicwino) - The Spotted Wing Drosophila (Drosophila suzukii), a relative newcomer in the United States, is a pest of Asian origin that attacks many different stone fruits including grapes. It was first spotted in California in 2008, quickly spreading up the Pacific coastline by 2009 and making its way across the United States by hitching rides with humans since they don’t fly very far on their own.

Basically, what happens is that the female Spotted Wing Drosophila (SWD) lays her eggs in the fruit, and then the developing larvae eat and otherwise do their business on that fruit, resulting in significantly reduced quality for wine making or anything else for that matter.

Compared with other fruits, however, some research has shown that grapes aren’t the best host for SWD survivorship, and that if grapes are already healthy and unscathed, only 0-9% of the larvae actually survives to adulthood. However, grapes that have been damaged by birds, disease, or something else have been shown to survive for a longer period of time, lay more eggs, and transmit Acetobacter bacteria into the grapes, all contributing to reduced grape quality and an overall economic loss for the vineyard.

A new study published in the Journal of Economic Entomology aimed to look into the effect of Spotted Wing Drosophila infestation on grape quality further, by looking at the infestation rates in vineyards in two different locations and to determine how various physiological traits of the grapes may or may not contribute to infestation rates by Spotted Wing Drosophila.

Brief Methods

Experiments were performed at vineyards in Trento Province, Italy, and Willamette Valley, Oregon during the 2011 through 2013 vintages.

Two separate experiments were performed: no-choice observational experiments, and choice observational experiments.

The grape varieties studied in Italy were: Chardonnay, Yellow Muscat, Traminer, Pinot Noir, Teroldego, and Schiava. No insecticides had been used on the grapes.

The grape varieties studied in Oregon were: Chardonnay, Pinot Gris, Pinot Noir, and Merlot.

All grapes were checked for SWD infestation prior to experimentation and only those SWD-free were used.

Penetration resistance was determined by pressing a 2-mm blunted needle into a grape until the point of penetration.