Risk assessment for the multicolored Asian ladybird beetle <em>Harmonia axyridis</em> in German fruit crops and viticulture

Abstract

The Multicolored Asian ladybird beetle Harmonia axyridis is an invasive species originating from East Asia. It was introduced to North America and Central Europe as a biological control agent. H. axyridis has spread all over these countries and has the capability to become an increasing problem for winegrowers. The Asian ladybird beetle feeds on damaged fruits in late summer and in autumn, especially on grapes. By being harvested and processed together with the grapes, it causes an off-flavor in the wine, the so-called ‘ladybird taint’ (LBT), due to the release of hemolymph (containing mainly methoxypyrazines) into the must. Sensory trials on wines produced in 2009 with added live beetles of H. axyridis showed that the LBT is detectable at a threshold level of 5 beetles/ kg where beetles were added to white ‘Riesling’ grapes. Modifications in wine processing conditions can reduce the LBT in wines. The sensory detection of LBT depends on the winemaking practices: the threshold level for crushed must fermented grapes was 3 beetles/ kg of ‘Pinot noir’ grapes compared to a threshold level of 6 beetles/ kg of ‘Pinot noir’ grapes that were must heat. In addition, the crushing of beetles in the wine press, and therefore the input of hemolymph into the must, can be reduced at pressures less than 2 bar and duration of pressing shorter than 60 minutes. Cudjoe et al. (2005) found that H. axyridis has a hundred-fold higher quantity of pyrazines in hemolymph than the 7-spot ladybird beetle Coccinella septempunctata. Interestingly, in our study, the wines contaminated by 7-spot ladybird beetle showed a significantly higher intensity of off-flavors then the wines contaminated by H. axyridis. Further analysis using headspace solid phase micro extraction (HS-SPME), gas chromatography–mass spectrometry (GC-MS), and GC-olfactometry (GC-O) showed, that in relation to C. septempunctata, the Multicolored Asian ladybird beetle had more nitrogen containing compounds in the hemolymph, mainly IPMP and 2-sec butyl-3-methoxypyrazine (SBMP). IPMP was detected as the main odor-active compound in both ladybird beetle species. 2-isobutyl-3-methoxypyrazine (IBMP), which occurred at a much lower frequency in H. axyridis, could be identified as a second intensive odor-active compound of the 7-spot ladybird beetle. SBMP, the second
highest measured N-compound of H. axyridis, had a lower olfactory active threshold by GC-O-test. C.  septempunctata contained less SBMP in its hemolymph than H. axyridis. Concentrations of IPMP in C. septempunctata and H. axyridis were between 2 -12 ng/ g beetle. In field-collected beetles no significant differences between the two species could be observed. Thus, concerning methoxypyrazine concentrations, H. axyridis cannot be regarded as more hazardous for viticulture than C. septempunctata. But we observed an effect of elytral pigmentation on IPMP concentrations. The succinea 2 type (orange without dots) had the lowest IPMP concentrations in two out of three feeding regimes compared to the succinea 1 (orange with dots) type. Depending on diet, IPMP contents differed in both species leading to higher concentrations in H. axyridis or C. septempunctata. Furthermore, aphid species ingested during larval development significantly affected IPMP content in adult beetles. For H. axyridis and C. septempunctata shaking proof is a significantly more efficient field monitoring method than yellow sticky traps. Due to their body size, both species
are able to escape from yellow cards and the population size might be underrepresented in data sets –also in the presented data in this study. However, in the years 2010 - 2011 H. axyridis were caught at highest abundance in fruit and field crops compared to other ladybird species. C. septempunctata and the 14-spot ladybird beetle Propylea quatuordecimpunctata were the second most abundant species. In addition, the invasive species H. axyridis was identified as a possible predator of grape phylloxera Daktulosphaira vitifoliae, a pest species in viticulture, in the laboratory and under field conditions. Even though grape phylloxera cannot be considered the optimum food for H. axyridis, it may represent a preferable food source if other food is rare or lacking in late summer. In conclusion, with regards to viticulture, H. axyridis can therefore have an ambivalent role as beneficial and pest insect.