Multicolored Asian Lady Beetles (MALB) and Fall Fruit: Why you should look before you eat

The recent cool temperatures and visages of browning corn and soybeans in the rural landscape are signs that fall is upon us.  One negative of the fall crops dying off is that some of the insects that were living in those fields are now looking for alternative food sources such as apples, grapes, and fall raspberries.

What is MALB?

Figure 1: Variation in Multicolored Asian lady beetle (Harmonia axyridis)

Multicolored Asian Lady Beetles (MALB) are a beneficial insect that often feeds on soybean aphids.  In the last few years soybean aphid populations have not been very high, but in 2023 there have been some isolated areas with high populations.  As a result, some fruit growers have seen increases in the populations of MALB.

Why is MALB an issue for fall fruits?

While MALB is a beneficial insect in soybeans, it can be a pest in fruit crops.  The most common issue with MALB is when is moves into fruit.  MALB seems to prefer soft fruits like raspberries and grapes, but I have also found MALB on apples that have bird or insect damage.  MALB are often seen in homes on windows and walls in the late winter or early spring.  If you have ever vacuumed them up, you are aware of the unpleasant odor that accompanies them.  That same odor is given off if they are accidentally ingested with fruit.  Some describe the odor/flavor as ‘nutty’, ‘earthy’, ‘moldy’, or ‘potato’.   While those descriptors don’t seem all that bad, unfortunately, I have had the experience of eating them in fall raspberries, and I can promise it’s not a pleasant experience. MALB is also a concern with fruits that are being harvested for processing into jams, juice, sauces, and wine.  The recommended thresholds vary, but there are suggestions that it takes as many as 1500 beetles per ton of fruit to taint the product to as little as 200 beetles per ton.  That would be a range from around 1 beetle every 5 to 40 clusters of grapes.

Figure 2: Multicolored Asian lady beetle (Harmonia axyridis), showing typical 'M' or 'W' between head and wing shields.

How to identify MALB

The color and number of spots on MALB can vary between each individual (Figure 1).  However, one consistent trait is that there is a ‘M’ or ‘W’ between the head and wing shields, depending on which way you are looking at the insect (Figure 2).  MALB also tends to be rounder in shape than many of the other lady beetles found in Iowa such as the Convergent or the Pink-Spotted Lady Beetle.

How to deal with MALB

While there are some insecticides that are labeled to control MALB, the short time between application and harvest makes using these products challenging.  The best way to prevent fruit from getting infested with MALB is timely harvest.  Fruit that is overripe, bird damaged, etc. are most likely to attract MALB.  For small batches of fruit, the beetles can be knocked off before eating them, but be sure not to crush them in the process, which will cause them to exude their foul odor.


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