# Assessing Wine Grape Cultivar Susceptibility to Spotted Wing Drosophila and Melanogaster-Type Drosophila in Hungarian Vineyards: Effects of Berry Integrity and Insights into Larval Interactions

## TL;DR

This study examines how different wine grape varieties in Hungary are affected by spotted wing Drosophila and other fruit flies, showing that grape condition and variety influence infestation levels.

## Contribution

The study identifies specific grape cultivars with varying susceptibility to SWD and MTD, and reveals how berry injury and pooling affect larval competition dynamics.

## Key findings

- Intact berries showed low infestation, but injury significantly increased fly emergence.
- Furmint was the most susceptible cultivar, while Cabernet Franc and Cabernet Sauvignon were less affected.
- Pooled samples favored MTD over SWD, indicating larval competition influences species dominance.

## Abstract

The spotted wing Drosophila (SWD) is an invasive pest that primarily targets thin-skinned fruits, while grapes are generally considered less susceptible. Our objective was to evaluate the importance of SWD as a primary pest in Hungary, as well as to get insight into its interaction with other melanogaster-type Drosophilas (MTD). Our results showed a consistent dominance of SWD in field traps in the grape ripening period. While intact berries showed a low overall level of infestation, there were significant differences in susceptibility among grape cultivars. Berry injury substantially increased the number of emerging flies and led to a higher proportion of MTD compared to SWD. This shift in species composition was even more pronounced when collected berries were maintained in pooled samples rather than individually isolated. Our findings highlight the role of SWD in the primary infestation of intact grape berries and underscore the importance of considering interspecific interactions when interpreting results based on fly emergence from field-collected fruits.

The invasive spotted wing Drosophila (SWD) represents new challenges for European and North American fruit producers. The aim of our study was to examine wine grape cultivar susceptibility to this pest and melanogaster-type Drosophila (MTD) by surveying drosophilid populations using field traps and conducting emergence tests. We assessed fly development from intact and artificially injured berries collected from four cultivars. Berries were incubated individually and in pooled samples to evaluate infestation patterns and potential larval interactions. Although grapes are generally considered less favorable hosts for SWD, the pest was consistently present across all vineyard plots. Infestation levels differed significantly among cultivars, with the Hungarian white cultivar Furmint being the most susceptible, while French-origin red cultivars Cabernet Franc and Cabernet Sauvignon, along with the other Hungarian cultivar Rózsakő, were less susceptible. Berry integrity played a crucial role: intact berries showed minimal infestation, whereas physical injuries led to a substantial and significant increase in infestation rates and fly emergence. In contrast to SWD-dominated trap catches and the nearly equal proportions of SWD and MTD observed in intact berries, injured berries were predominantly colonized by MTD. This dominance became even more pronounced in pooled samples, suggesting that larval competition in shared environments favors MTD over SWD. These findings underscore the importance of grape cultivar traits and berry condition in shaping Drosophila infestation dynamics. Further research into the chemical and ecological drivers of host selection and interspecific interactions is warranted to improve vineyard pest management strategies.