Mexican Bean Beetle

The Mexican bean beetle (Epilachna varivestis) is a ladybug that eats plants instead of insects. It belongs to the lady beetle family, but unlike its aphid-eating cousins, it feeds on the leaves of bean plants, which makes it a serious garden and farm pest.

Mexican bean beetle Quick Facts

Common name	Mexican bean beetle
Scientific name	Epilachna varivestis
Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Coleoptera
Family	Coccinellidae
Genus	Epilachna
Type	Insect (lady beetle)
Diet	Bean leaves, plus other legumes such as soybeans and clover
Habitat	Gardens and farm fields where beans grow
Native range	Mexico; now also across the eastern United States
Size	About 6-8 mm (1/4 in)
Colours	Copper to yellowish-orange with 16 black spots
Special feature	A plant-eating ladybug, unlike most of its relatives

Where Does the Mexican Bean Beetle Live?

As its name suggests, this beetle is native to Mexico. It spread into the southwestern United States long ago, and in the early 1900s it was accidentally carried east. Since then it has become common across much of the eastern United States and parts of southern Canada. It also lives in some irrigated farming areas of the West. It does poorly in very dry places.

What Does It Look Like?

The adult Mexican bean beetle is about 6 to 8 mm (about 1/4 inch) long and shaped like a rounded dome. It is copper, yellowish-orange or tan, with 16 black spots arranged in three rows across its back, eight on each wing cover. Newly emerged adults are pale yellow and darken as they age.

Because it looks so much like a helpful ladybug, it is important to identify it carefully before taking action. Its coppery color, its 16 spots and the fact that you find it on bean plants are good clues.

The larvae are bright yellow to orange, about 8 mm (1/3 inch) long when grown, and covered in rows of soft, branched spines. They do have six short legs, but the spines make them look fuzzy. The eggs are oval and yellow-orange, laid in neat upright clusters on the undersides of leaves.

What Does It Eat?

Mexican bean beetles feed mainly on beans. Favorites include common beans such as green, snap and kidney beans, plus lima beans. They also eat soybeans, cowpeas and mung beans, and sometimes other legumes such as clover and Alfalfa.

Adults and larvae usually feed on the underside of the leaves. They scrape away the soft green tissue between the veins but leave the thin top layer, so the leaf ends up looking like lace. This is called skeletonizing. When there are many beetles they may also chew bean flowers, pods and stems. The larvae do most of the damage.

In the same way that the Japanese beetle leaves skeletonized leaves behind in gardens, the Mexican bean beetle can quickly strip a bean patch if it is not spotted early.

Life Cycle

The Mexican bean beetle goes through complete metamorphosis: egg, larva, pupa and adult.

• Winter: Adults spend the winter sheltering in leaf litter, plant debris and woodland edges near fields.
• Spring: As the weather warms, usually in late spring, adults fly to bean plants to feed. After a week or two, females start laying eggs.
• Eggs: Each female can lay several hundred eggs in her life, in clusters of about 40 to 60 on the undersides of leaves. The eggs hatch in about one week in warm weather, or up to two weeks when it is cool.
• Larvae: The larvae feed for about two to five weeks, molting several times as they grow.
• Pupae: The larva attaches itself to the underside of a leaf and pupates. About a week later, a new adult emerges.

In the north there may be just one generation a year, while warmer areas can have two or three.

As a Pest

The Mexican bean beetle is one of the most damaging pests of beans in the eastern United States. If many larvae are feeding at once, bean plants can lose most of their leaves, which weakens them and reduces the harvest. Hot, dry weather tends to keep their numbers down, while mild, humid summers can lead to outbreaks.

How to Control Mexican Bean Beetles

Gardeners can usually keep this beetle in check without chemicals:

• Check the undersides of bean leaves often, and crush yellow egg clusters and spiny larvae.
• Hand-pick adults and drop them into a container of soapy water.
• Cover young bean plants with lightweight row cover fabric until they flower.
• Plant early bush beans, which may be harvested before beetle numbers build up.
• Clear away old bean plants and debris after harvest, so fewer adults survive the winter.
• Encourage natural enemies. A tiny wasp called Pediobius foveolatus attacks the larvae and is sold for release in gardens and farms. Spined soldier bugs also eat the larvae.

Remember that most other ladybugs are helpful predators, so leave them alone.

Mexican bean beetle FAQs