Mexican Bean Beetles in the Home Vegetable Garden
The Mexican bean beetle can be simply described as a slightly larger, yellow, and leaf-eating variation of the otherwise beneficial lady beetle (ladybug). They are absolutely identical to one another, save color and size.
Another more accurate name for the Mexican bean beetle might be the “legume” beetle because they’re not choosy as to which legume they infest. First localized to lima, bush, and pole beans in the southern states, the Mexican bean beetle has since naturalized throughout most of North America feeding on any and all legumes from field bean, adzuki, mung, soy, to alfalfa and clover.
Mexican bean beetles don’t always swarm like Japanese or Colorado potato beetles, but can be found alone feeding on your legumes with only minor shot holes and bites taken from the leaves.
This is the one ladybug you do not want in your garden.
Facts About Mexican Bean Beetle Garden Pests
- Mexican Bean Beetle Distribution: Native to the southern states, now naturalized all throughout east of the Rockies
- Mexican Bean Beetle Host Plants: Any field bean and legume including adzuki, mung, soy, chickpea, clover, and alfalfa
- Mexican Bean Beetle Lifespan: ~9-12 months
- Mexican Bean Beetle Eggs Laid per Lifetime: ~600
- Mexican Bean Beetle Removal: Removal of eggs by hand, predatory insects, neem oil, castile soap, BT spray (Bacillus Thuringiensis)
- Mexican Bean Beetle Predators: Spiders, lacewing, tachinid fly, ground beetle, grasshopper, birds
- Most Common in North America: Common Mexican Bean Beetle (Epilachna varivestis)
What Do Mexican Bean Beetles Look Like?
Mexican bean beetles are actually a leaf-eating species of lady beetles (ladybugs) and share the same exact spotting you’ve come to know and love, but with a yellow-orange body instead of red.
Mexican bean beetles are much larger than lady beetles and generally change to a shade of copper in the later season. Larval grubs of Mexican bean beetles have a similar shape and appearance to adults but are noticeably very spiny, almost appearing to have several sets of legs.
Although different in diet and distribution, the related squash beetle is often mistaken for the Mexican bean beetle, having a more amber coating as opposed to bean beetle yellow. Regardless of type, all lady beetles share the same hardshell scarab body and are typically found within the orange-red color spectrum.
Mexican Bean Beetle Damage to Garden Vegetables
Damage caused by Mexican bean beetles is often characterized as having a “skeletonized” or laced appearance caused by the young larvae only eating the underside of a leaf. As the larval grubs hatch on the underside of a leaf, they will immediately begin to feed on the same protective underside, not the entire leaf, which causes the untouched outer portion of the leaf to dehydrate with a veiny and lacey look.
Adult Mexican bean beetles are responsible for the skeletonizing and defoliation of host plants, but they are also known to cause damage to fruiting pods, especially in regular field beans (Phaseolus vulgaris). Mexican bean beetles don’t always swarm and infest, but can be found alone feeding on your legumes with minor shot holes and bites taken from the leaves.
What Do Mexican Bean Beetles Eat in the Garden?
Another more accurate name for the Mexican bean beetle might be the “legume” beetle because they’re not choosy as to which legume they infest.
Although first localized to lima, bush, and pole beans in the southern United States, the Mexican bean beetle has since been naturalized throughout most of North America feeding on any and all beans and legumes from adzuki, mung, soy, to alfalfa and clover.
Adult bean beetles generally will feed on both the fruiting pods and vegetation while the soft-bodied larvae only chew on leaves.
The 24-Spot lady beetle is a bright red leaf-eating beetle known to feed on a wide range of ornamental flowers. Although they’re found in nearly every east of the Rockies, Mexican bean beetle still prefers legumes known to thrive in the southwest such as chickpea, kidney, and lima.
Mexican Bean Beetle Eggs
Eggs are generally easy to spot on the underside of host plants, as they are bright yellow, chicken egg-shaped, and similar in shape and size to several other garden pest eggs. Adult females generally lay clusters of 40-75 eggs at once, totaling an average of about 600 per lifetime.
Like many of leaf-eating beetles, eggs of the Mexican bean beetle hatch in about 14-21 days, giving home gardeners just enough time to try and remove them by hand before hatching. Finding and removing the eggs early enough is the best way to control a possible bean beetle infestation.
Eggs are not just laid on the underside of leaves for safety, but as an immediate food source for the Mexican bean beetles to feed on through all four larval stages and into adulthood.
How To Rid Mexican Bean Beetles from the Garden
Like many beetles, one of the most effective ways to minimize an infestation is to locate the eggs early and remove them by hand.
Sprays such as neem oil, castile soap, and BT spray (Bacillus Thuringiensis) are known only to be effective while the Mexican bean beetle is still a soft-bodied larva. Adult pupae are more difficult to kill once they’ve developed their wings and hardshell scarab-like body.
Organic diatomaceous earth and kaolin clay can be spread on the plant and surrounding soil to help combat both larvae and adults.
Lady beetles (ladybugs) are generally one of the most highly recommended insects to help rid a garden of an infestation. However, because the Mexican bean beetle is a type of lady beetle, there are not too many natural predators to it other than the typical spider, bird, ground beetle, tachinid fly, or parasitic wasp.