Land usage around vineyards and its effect on spotted wing drosophila populations and varietal preference testing in Virginia grape growing regions

Drosophila suzukii, also known as the spotted wing drosophila (SWD), is a pest of wine grapes and berry crops in Virginia.  In order to ascertain if certain grape varieties were more susceptible to SWD attack both choice and non-choice tests was conducted in the Summer / Fall of 2013.  Six grape varieties were chosen based on their skin color and thickness.  Brix and penetration force data were also evaluated, since sugars increase as the grapes ripen.  The tests were repeated weekly for four weeks with 12 replicates each for the choice test and four replicates each of the non-choice test.  The experiments were conducted after the onset of véraison when grape sugars are just starting to accumulate.  Fifteen male and female SWD were placed in mesh rearing cages with a 20 gram sample of each of the six grape varieties.  The SWD adults were allowed to remain in the cages for four hours.  Grapes were then placed in plastic rearing cups and monitored for 21 days.  All flies that emerged were collected, counted and identified.  An ANOVA was used to evaluate the data.  No varietal differences were detected in the choice test results.  However, in the non-choice test significantly more SWD adults emerged from the Petit Manseng and Viognier varieties.  The field populations were too low to modify our conclusions.