Ladies bugs, or lady beetles, are always welcome in the garden, except when they’re not. Because, if it’s a Mexican bean beetle, it’s the last thing you want to see in your garden!
Mexican bean beetles are found throughout Mexico and much of the eastern U.S., and in areas west of the Rockies that receive a lot of rain or irrigation. These pests have been found in and eradicated from California once. Let’s find out why Mexican bean beetles are so bad.
Mexican bean beetle identification
Mexican bean beetles look like ladybugs, sort of. They have the same oval, domed shaped, and they have spots. To be exact, Mexican bean beetles have eight black spots on each side. These evil cousins to ladybugs can range in color from golden yellow to a rusty brown. Larva look like spiny oval pills and the eggs are yellow. Pupae are found hanging from the underside of leaves.
Mexican bean beetle lifecycle
In late spring, adults emerge and begin feeding and breeding. Each female will lay hundreds of eggs in clusters on bean leaves. When these eggs hatch, the real damage begins. Heavy infestations can defoliate an entire field of legumes. After a few weeks of feeding, the larvae enter a pupal stage. Newly emerged adults often travel long distances in their search for food.
Mexican bean beetles (Epilachna varivestis) are a type of lady beetle that eats plants, rather than other insects. In particular, these pests feed on legumes. That means your cowpeas, mung beans, soybeans, green beans, wax beans, lima beans, peas, and fava beans are at risk. It also means you need to monitor any alfalfa, peanuts, wisteria, lupins, tamarind, carob, and lentils for signs of Mexican bean beetle feeding.
Mexican bean beetle damage and control
Adult beetles feed on the undersides of leaves, leaving them skeletonized. Beetles may also feed on fruit and flowers. The larvae eat even more than the adults! Luckily, parasitic wasps can do a lot to reduce bean beetle populations, so avoid using broad spectrum pesticides and insecticides. You can also use row covers when you know that Mexican bean beetles are present or likely to appear. As always, take the time to quarantine new plants.
If you live in California and suspect seeing a Mexican bean beetle, please try to capture it and report it to the California Pest Hotline at 1 (800) 491-1899, or contact your local Department of Agriculture.
You can grow a surprising amount of food in your own yard. Ask me how!