MALB look like most native lady beetles. Their color can range from tan to yellow to orange to red. Their wing covers can have from 0 to 19 black spots on them. But MALB can be identified by a characteristic “M” on their pronotum, the region behind their heads.
Overwintering adults emerge from hibernation to lay groups of bright yellow oblong 1.2 mm long eggs, most often on plants with aphid activity. The larvae are very effective biocontrol agents, eating aphids and other soft-bodied pest insects. There are four larvae instars that look like miniature alligators. The last instar pupates without a cocoon and an adult emerges. The life cycle from egg to adult to egg takes about three to four weeks depending on temperature and food abundance. The lower threshold for development is 11.2°C. Adults typically live 30 to 90 days; however, they may live up to three years. There are 5-6 generations per year.
In late September to early October, populations of the normal prey that MALB consumes, (aphids, scales, etc.) decline dramatically and temperature cues initiate the overwintering process for MALB. Dispersal flights into vineyards generally occur on warm days after days with near-freezing temperatures. Adults search out sugar-rich food to build up their reserves for overwintering. They will mainly aggregate where diseases, birds, or other insects have already opened the berries up. MALB do not cause significant feeding damage, but when accidentally harvested with the grapes will taint and spoil an entire batch of wine, possibly causing significant economic loss.
“Lady beetle taint”
MALB protects itself from predators through the multiple color morphs, which may confuse some predators and the presence of alkaloids that it can secrete to repel potential enemies such as birds and other insect feeders. The secretion is referred to as “reflex bleeding” and is a defensive response. MALB force some haemolymph (blood) that contains these alkaloids from the joints of its legs. Reflex bleeding produces a smell described as rancid peanut butter and produces an undesirable taste to most predators.
This substance, 2-isopropyl-3-methoxypyrazine (IPMP), causes peanut, bell pepper, asparagus, and earthy/herbaceous aromas and flavors in wines and can mask or reduce the varietal fruit characteristics of the wine. If MALB are aggregated on a cluster of berries, and are not dislodged during harvest, they may be harvested with the clusters. If they are not removed prior to crushing and are present during the subsequent winemaking operations, the finished wines can develop off‐aromas and flavors, generating a taint commonly known as ‘ladybug taint’.
Monitoring and Thresholds
A threshold of 200-400 MALB per tonne of fruit has been suggested. MALB that are dead for 3 days or more do not result in taint, whereas live MALB or those dead for only 1 day may result in taint. However, many processors have much lower thresholds so please contact your buyer/processor directly to determine if controls are required to meet buyer needs.
Begin monitoring for MALB several weeks prior to anticipated harvest date. Ten to 20 panels (throughout the block or cultivar) should be chosen in an average vineyard and at least five vines should be examined carefully at each panel. Due to the high potency of IPMP, as few as one beetle per vine can be sufficient to affect the final wine.
These beetles can appear suddenly in vineyards so it is recommended to monitor daily for each cultivar in the last seven days before harvest. For an outbreak year of Asian lady beetle, there are three key components:
- high aphid populations in host plants on which they feed (especially soybeans)
- a long warm fall switching to a period with cold night temperatures (less than 5-10°C) followed by warm days
- ripe fruit present when beetles start searching for overwintering sites.
Minimize fruit damage
MALB population density increases as the incidence of berry injury, due to other causes, increases. Protect berries by avoiding splitting (physiological/water stress) or damage by birds or insects such as grape berry moth, wasps and spotted wing drosophila. Varieties with tight clusters may have a higher percentage of splitting, and will usually attract more lady beetles. Strategies to reduce berry splitting include treatments to loosen clusters such as bloom leaf stripping or sprays of gibberellic acid during bloom. Water management is also important: cover crops will take up some of the moisture that promotes berry swelling during the pre-harvest period.
There are currently only 2 insecticides registered for control of MALB in grapevine: Malathion 85E and UP-Cyde (cypermethrin). The preharvest interval for Malathion 85E is 4 days for hand harvest and 3 days for machine and for UP-Cyde it is 6 days and 2 days, respectively. Cypermethrin has longer residual activity against MALB. It is especially important to take into consideration the pre-harvest interval when considering a spray program for MALB, since this is a pest that moves into the vineyard only shortly before harvest. As always, make sure to read the label before using any pesticide. It should also be kept in mind that while not as intense as with live beetles, dead MALB can still taint wine between 3-6 days post mortem.
Because MALB tend to hide inside clusters during cool nights, some growers use the strategy of spraying at night so that the MALB are exposed to residues when they emerge the next day.
Several botanical extracts show promise in lab and field trials. Unfortunately, MALB populations were not high enough to validate all of these products in vineyards. In lab trials, carvacrol (a component of oregano oil), Timorex Gold, pine oil, and granite dust were highly effective and reduced the number of the beetles on grapes by more than 80%. Timorex Gold, potassium metabisulfite, basil oil, granite dust, and Ecotrol EC decreased in repellency from 24 to 72 hours. Pine oil was the most repellent compound, and it remained consistently repellent over the 72-hour test period in the lab. In field trials, KMS at 10 g/L consistently reduced the number of MALB on grapevines 24 h after application. Buran, Biobenton and Sulfobenton had efficacy as well. While none of the alternatives were as effective as cypermethrin, if the number of beetles in a vineyard exceeds the established sensory detection threshold, a repellant could drive them to disperse and reduce the number of beetles below the threshold level.
Since MALB release IPMP during crushing and destemming, if they can be removed before that process, ladybug taint may be minimized.
Shaker tables are effective at separating them from the fruit, thus preventing extraction of MPs from the beetles during grape processing. The shaking motion forces beetles through the mesh into a collection and disposal area below.
New harvesters offer an optional destemmer that separates the berries from the stems, roller sorting tables and an air cushion that blows out any Material other than grapes (MOG), including MALB.
Optical sorters employ combinations of destemmers, shaker tables and high-speed cameras and image-processing software to quickly scan and sort destemmed grapes to remove all MOG including MALB.
From the vineyard to the winery
MALB can rapidly move into harvested clean fruit in open-top bins in the field or at the winery. Ensuring a tightly fitting lid that is not removed until sampling at the winery will prevent MALB from contaminating loads of fruit.