Effects of germicidal ultraviolet-C light on grape mealybug (Pseudococcus maritimus)

Abstract

Germicidal ultraviolet-C light (UV–C) has been used to effectively suppress grapevine powdery mildew (Erysiphe necator). However, effects on arthropod pests that would be simultaneously exposed to UV-C during applications directed at E. necator, are poorly understood. The grape mealybug (Pseudococcus maritimus) is one such grapevine pest. We exposed mated P. maritimus adult females in a lab study to UV-C light doses of 100, 200, 500 and 1000 J/m2. UV-C was applied during darkness and was followed by an additional 4 h dark period post-treatment to enhance possible suppressive effects of UV-C. Positive (2% horticultural oil) and negative (untreated) controls were included. Adult female P. maritimus oviposition was observed two weeks after treatment, and hatching of eggs was enumerated four weeks after treatment. UV-C treatment of mated adult females, regardless of dose, did not prevent oviposition or reduce ovisac viability. In a separate lab experiment, first instar P. maritimus nymphs were similarly exposed to UV-C doses of 200 and 1000 J/m2 with and without a 4hr dark period. UV-C treatments were compared to the same positive and negative controls. Nymph mortality was assessed at 24 and 48 h after UV-C treatment. Increasing doses of UV-C treatments, followed by a dark period, had a small, but significant impact on nymph mortality relative to the untreated control. Further studies on the potential sublethal effects (e.g., fecundity or longevity) of single or multiple exposures or increased UV-C doses upon juvenile stages of P. maritimus are warranted, as longer-term and multigenerational effects of UV-C have been observed in other arthropod systems.