Summary of recent MALB research findings from the Cool Climate Oenology and Viticulture Institute, Brock University

Morbidity of Harmonia axyridis mediates ladybug taint in red wine

Insecticidal sprays in the vineyard have been advocated to mitigate the problem, however the resulting dead beetles are often incorporated in with the grape bunches during harvesting operations. The main objective of this study was to quantify the impact of dead MALB on LBT in red wine. Duplicate wines were produced from Cabernet Sauvignon with the addition of 10 beetles/L juice, added beetles that had been dead for 1, 3, 7, or 60 days. A control wine with no added beetles was also included. Finished wines were evaluated using a trained sensory panel and descriptive analysis. The intensities of aroma and flavour attributes associated with ladybug taint were highest in live beetle wines. Results suggest that MALB that had been dead for 3 days did not affect wine quality. The higher the concentration of IPMP, the greater the intensity of 6 atypical aroma and flavour attributes associated with ladybug taint.

Determination of the critical stages of processing and tolerance limits for Harmonia axyridis for 'ladybug taint' in wine.

It is not known when IPMP is transferred from MALB (e.g. in the vineyard onto grapes or during must processing) nor what MALB densities are required for production of 'ladybug taint' in the final wines. This study sought to clarify these issues through three trials. In the first, MALB were added to Riesling grapes or juice at different stages of processing (harvest, crush/destem, pressing or directly to juice), & the resultant wines were analysed chemically & sensorily. The presence of MALB during processing had minimal effect on the basic composition & the spectral properties of the wine. IPMP was detectable only after the direct addition of MALB to the juice. Sensorially, control wines (no added MALB) could be differentiated from wines made after MALB were added at crushing/destemming (at 3 beetles per kg grapes), whole bunch pressing & when added directly into the juice, but not when MALB were added & subsequently removed from a simulated harvest treatment or when added during crushing/destemming at 0.3 beetles per kg grapes. In trials 2 & 3, sensory detection thresholds for 'ladybug taint' were established for white & red wines produced with known densities of MALB. Estimates of 'tolerance limits' in the vineyard were then calculated using regression models, & correspond to 1530 & 1260 beetles/tonne grapes for white & red wines respectively. However, given the range of grape & wine processing options available to producers, many of which are not accounted for in this study, we recommend that a more conservative limit of 200-400 beetles/tonne grapes may be appropriate.

Ripcord 400 EC (pre-harvest interval 7 days) and Malathion 500E (pre-harvest interval 1 day) are registered for control of MALB. A minor use study is underway to examine reducing the pre-harvest for Ripcord.

This study evaluated the efficacy of a number of commercially available fining agents & other interventions on reducing 2-isopropyl-3-methoxypyrazine (IPMP) concentration & taint characteristics of white & red wine affected by MALB. The fining agents & other treatments were selected after a series of bench-tests to identify the most promising approaches. Wines fermented in the presence of MALB beetles were treated with activated charcoal, bentonite, oak chips, deodorized oak chips & either ultraviolet (red wine) or visible (white wine) light. Activated charcoal was successful at reducing IPMP concentration in white wine & deodorized oak in red wine, although this did not generally translate into lower intensity of the sensory attributes associated with LBT. Oak chips were successful in reducing the intensity of MALB-taint characteristics in both white & red wines, probably through a masking effect. Other processes investigated, including the non-traditional use of deodorised oak, UV & visible light, generally had no effect on white wine & limited effect on red wine. While research is on-going to investigate methods for preventing MALB beetles from entering the juice & winemaking process, further investigation is also required to develop appropriate technologies to remove LBT from juice & wine.

Yeast strain affects IPMP concentration and sensory profile in Cabernet Sauvignon wine

This study sought to determine the influence of commercial Saccharomyces yeast strains on IPMP concentration in Cabernet Sauvignon wines and to examine their sensory effect. Re-hydrated juice from Cabernet Sauvignon concentrate was spiked with IPMP and fermented with Lalvin EC1118, Lalvin BM45, Lalvin ICV-D21 or Lalvin ICV-D80. Addition of IPMP to juice resulted in higher intensity scores for earthy/peanut/musty aroma, green pepper aroma, canned green vegetable flavour and nutty/peanut flavour, all characteristics previously associated with ladybug taint. Yeast strains differed in their sensory impact on wine made from IPMP-spiked juice for 5 aroma and 4 flavour attributes. The authors caution against fermenting with D80 or BM45 in juices with high IPMP concentration and recommend D21 as a desirable strain under these conditions.

Seven-spot lady beetle proves as potent as MALB

The seven-spotted lady beetle (SSLB) is as potent as the multicoloured asian lady beetle (MALB) in terms of causing ladybug taint in wines. Results that show, under practical winemaking conditions, SSLB secretes as much IPMP in wine as MALB. The ladybug taint potency of SSLB by measuring and comparing the levels of IPMP in wines made from Vidal and Cabernet Sauvignon grapes, which were treated in separate lots with known quantities of either SSLB or MALB, and then processed into wine using commercial winemaking techniques.
If SSLB is indeed as potent as MALB, it is likely that its quality control limit in the vineyard will be similar to that for MALB. But further research is required to confirm this theory and the preliminary results of the SSLB study. One benefit of the SSLB finding is that growers and wineries should no longer have to differentiate between the two species of beetles when assessing fruit quality on the vine or in harvest bins. It's important to note that SSLB are typically not as prevalent as MALB in vineyards during harvest.

Multicoloured asian lady beetle, left, and seven-spotted lady beetle.
Photo: Cheryl Moorehead (left) and Stan Reinbold (right)

Learn more:

• CCOVI MALB webpage, Brock University

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