In the southeastern United States, the Japanese beetle [JB], Popillia japonica Newman, and the green June beetle [GJB], Cotinis nitida L., are key pests of grapes (Vitis spp.). Their flight periods overlap in Kentucky, peaking in late July and early August, coincident with the later stages of berry ripening for many cultivars. JB severely defoliate vines, whereas both beetles feed upon ripe fruits. Management relies primarily on repeated insecticide applications, but spray restrictions limit near-harvest use of many products.
This research indicates that grape cultivars vary in susceptibility and response to defoliation by JB. Some varieties (e.g., Norton) showed reduced vine growth, delayed post-veraison increase in total soluble sugars and pH, as well as reduced cluster number and weight, berries per cluster, and yield. Other varities (e.g., Concord) showed little or no measurable impact from JB. Notably, the biweekly carbaryl spray regime was as effective as weekly sprays in mitigating the impacts of defoliation.
Berries of many early- and mid-season ripening cultivars reached near-harvest or harvest sugar levels during peak beetle flight. These cultivars recruited the greatest number of GJB feeding aggregations resulting in> 95% crop loss. However, small (1-2 wk) phenological differences in berry characteristics, particularly berry toughness and sugar content, translated to marked differences in injury, such that cultivars that ripened after GJB flight had waned sustained little or no damage.
JB was shown to physically facilitate GJB feeding by biting into ripe grapes too tough for the latter species to penetrate, creating focal points for GJB feeding. JB further promotes GJB injury by contaminating fruits with yeasts. Such yeasts produce volatiles exploited by both sexes of GJB as host-locating and aggregation kairomones. Thus, wounding of even a few berries by JB can induce GJB feeding aggregations.
Research presented in this dissertation supports sustainable pest management for conventional and organic production systems by clarifying impacts and interactions of two key vineyard pests in the Southeast, and by identifying cultivars and strategies that reduce the need for chemical input.
Keywords: Vitis sp., Japanese beetle, green June beetle, insect-plant relationships, viticulture