Alexa McDaniel,* David Gadoury, and Michelle Moyer
*Washington State University, 24106 N Bunn Rd, Prosser, WA, 99354
(alexa.mcdaniel@wsu.edu)

Ultraviolet-C (UVC) radiation has been used to effectively suppress grapevine powdery mildew (Erysiphe necator), though its effect on pests such as the grape mealybug (Pseudococcus maritimus) is unknown. Our objective was to determine the potential lethal effects of UVC treatments to grape mealybug. We exposed P. maritimus nymphs to UVC doses of 100, 200, 500, or 1000 J/m2 using a laboratory UVC lamp array. There was no dark period after treatment. UVC treatments were compared to an untreated control and a positive control (2% v/v horticultural oil PureSpray Green). Bioassays were assembled using groups of ten first instar nymphs per grapevine leaf disc; individual leaf discs were placed on a moistened cotton round in a petri dish. Bioassays were maintained in an incubator with a day:night ratio of 16:8 hr at 21°C. Treatments were replicated five times and the experiment was repeated three times. At 2, 24, and 48 hrs after treatments, the mortality of the nymphs was assessed and recorded. Mortality of nymphs was measured by their response to prodding. Post-prodding movement indicated viability; lack of movement was assumed to indicate mortality. No UVC treatments increased acute nymph mortality over the untreated control. Even a UVC dose of 1000 J/m2, which is five to 10 times higher than doses used against E. necator, did not increase nymph mortality compared to the untreated control (p = 0.57, 0.99, and 0.43 for 2, 24, and 48 hrs posttreatment, respectively). Although UVC did not increase acute mortality in grape mealybug nymphs, longer-term and multigenerational effects have been observed in other arthropod systems (e.g., phytophagous mites). Further studies on the chronic and potential sublethal effects (e.g., fecundity or longevity), or effects of multiple UVC exposures, are warranted.

Funding Support: Washington State Wine Commission