Brown marmorated stink bugs (Halyomorpha halys) have been observed at all life stages in affected vineyards in Europe and North America. Damage to grape bunches can be caused by all growth stages except for the newly hatched first nymph stage (Basnet et al. 2015, Tomasino 2013). Grapevines are considered susceptible to brown marmorated stink bug (BMSB) damage from the point of fruit set.
BMSB feeding site damage
BMSB feeding begins with the insertion into the grape berry of the stylet (sharp mouthpart) and the injection of watery saliva containing digestive enzymes, causing the cellular breakdown of host-plant tissue that enables the pre-digested contents to consumed as a liquid (Leskey et al. 2018).
BMSB feeding on grapes leads to soft sunken areas at the feeding site that become slowly discoloured. Damage incurred post-veraison is most severe and results in black necrotic spots that grow with time, resulting in berry deformation (Basnet 2014).
Secondary infection after feeding damage
The mechanical damage and digestive-enzyme breakdown of tissue around the feeding site increases susceptibility to secondary infection by bunch rots such as Botrytis and sour rot, which in turn affect yield and quality. In the US, it is reported that the presence of five BMSB per grape bunch may lead to 37% loss in yield of Chardonnay and 30% in Concord (juicing grapes) (Smith et al. 2014).
How can brown marmorated stink bugs taint wine?
As with other stink bugs, BMSB release a strong and unpleasant odour when disturbed. The volatile molecules (such as trans-2-decenal) excreted by BMSB as a defensive compound have the potential to taint grape juice and wine if BMSB end up in harvested grapes. Trans-2-decenal gives wine a strong aroma described as ‘green’ and ‘coriander-like’ even when present in very small concentrations. Additionally, the presence of trans-2-decenal leads to a reduction in positive fruit aromas.
Winery treatment options for tainted wine
To date, fining treatments have not been found to be successful in removing trans-2-decenal from tainted wine. Reverse osmosis treatment of affected wine has achieved small decreases in taint character. Currently the best treatment option for affected wine may be ageing under reductive conditions, which appears to result in the degradation of trans-2-decenal. The exact mechanism responsible for the degradation of trans-2-decenal by this method is not understood (Mohekar et al. 2018).