Mexican Bean Beetle

Mexican bean beetles are considered a serious pest in many areas and can cause significant damage to legume crops, including beans, peas, and soybeans.

Host Plants

Mexican bean beetles are pests of legume crops, including beans and peas, and are particularly attracted to plants in the genus Phaseolus. Some of the most common host plants include:

• Snap beans (Phaseolus vulgaris)
• Lima beans (Phaseolus lunatus)
• Runner beans (Phaseolus coccineus)
• Soybeans (Glycine max)
• Peas (Pisum sativum)
• Lentils (Lens culinaris)

Regions impacted

Mexican bean beetles are native to Central America and Mexico but have been introduced to other parts of the world, including the United States. In the United States, they are commonly found in the eastern and central regions, from Florida to the Great Plains and from the Gulf of Mexico to the Great Lakes. They are also found in parts of Canada, including southern Ontario and Quebec.

Description

Mexican bean beetles are small, oval-shaped insects that are yellowish-brown in color and have 16 black spots on their wings. They measure about 1/4 inch long and 1/3 inch wide and have a round or slightly oblong shape.

They have a distinctive appearance, with their yellowish-brown color and black spots, making them easy to recognize.

Life Cycle

Mexican bean beetles have a complete metamorphosis, going through four life stages: egg, larva, pupa, and adult. The life cycle can be completed in about 4-6 weeks, depending on temperature and other environmental conditions.

• Egg stage: Female beetles lay clusters of yellowish-orange eggs on the undersides of leaves. The eggs hatch in about 5-7 days, depending on temperature.
• Larva stage: The newly hatched larvae are yellow and spiny, and they feed on the leaves of legume crops. They molt several times as they grow, and they can reach a length of about 1/2 inch. The larvae feed for about 10-14 days before pupating.
• Pupa stage: The larvae form pupae, which are brown and about 1/3 inch long. The pupae are found on the undersides of leaves or on the soil surface.
• Adult stage: The pupae emerge as adults, which are yellowish-brown and have 16 black spots on their wings. The adults feed on the leaves of legume crops and mate, starting the cycle over again. Female beetles can lay up to 500 eggs during their lifetime.

Damage and Detection

Damage: Mexican bean beetles feed by sucking the sap from the leaves of legume crops, causing the leaves to become skeletonized, discolored, or wilted. The damage is most severe when the beetles are present in high numbers. They can also reduce the yield and quality of the affected crops, making them a serious pest in many areas.

Detection: Mexican bean beetles are relatively easy to detect due to their distinctive yellowish-brown color and 16 black spots on their wings. Adult beetles can be found on the leaves of legume crops, and larvae and pupae can be found on the undersides of leaves or on the soil surface. It’s important to monitor the presence of Mexican bean beetles in the garden and to implement control measures if necessary.

To detect Mexican bean beetles, look for the following signs:

• Yellowish-brown adult beetles on the leaves of legume crops.
• Yellow and spiny larvae on the undersides of leaves or on the soil surface.
• Discolored or wilted leaves on the affected plants.
• Skeletonized leaves, with the veins and midribs remaining intact.

If you suspect that you have Mexican bean beetles in your garden, it’s important to take action to control them, as they can cause significant damage to legume crops.

Prevention and Control

There are several methods that can be used to control Mexican bean beetles in the garden, including both chemical and non-chemical methods. Here are some of the most effective methods:

• Plant early-season bush beans: This can be an effective way to avoid the main generations of Mexican bean beetles. Mexican bean beetles have several generations per year, and planting early-season beans can help to avoid the most damaging generations. By planting beans early in the season, you can harvest your crop before the beetles can lay their eggs and cause significant damage.
• Row covers: Cover the affected plants with row covers to exclude these beetles. Make sure to remove the covers when the plants begin to flower to allow for pollination.
• Handpicking: Remove adult beetles and larvae from the affected plants by hand and drop them into a bucket of soapy water to kill them. This method is most effective when there are only a few beetles present.
• Insecticidal soap: Apply insecticidal soap to the affected plants to kill these beetles. The soap coats the beetles, causing them to dehydrate and die.
• Companion planting: Plant companion crops, such as garlic, marigolds, nasturtium, rosemary, or summer savory, which are known to deter Mexican bean beetles.
• Neem oil: Apply neem oil to the affected plants to control Mexican bean beetles. Neem oil works by disrupting the beetles’ ability to feed and mate and can also repel them.

It’s important to use a combination of these methods to effectively control Mexican bean beetles in the garden, as no single method will provide complete control. It’s also important to monitor the affected plants regularly and to take action if the beetles return.