Mexican Bean Beetle: How to Identify, Prevent and Get Rid of Mexican Bean Beetles

Scientifically known as Epilachna varivestis, it is one of the most destructive pests that affect beans. It is a member of the Coccinellidae family, which include beneficial insects. However, the same family also includes this beetle, which can lead to serious infestation. With this, it is important that you know how to get rid of Mexican bean beetle.

When they are eggs, their length is about 1.3 millimeter and the width is .6 millimeter. They usually have a yellow to orange color. Meanwhile, the larva is about 1.6 millimeters after hatching and can grow as long as 9.5 millimeters when it reaches maturity. The color is usually yellow to green. As soon as it turns into a pupa, it will become yellow and spineless. Upon reaching the adult stage, the Mexican bean beetle usually has a length of 7 millimeters. When it is young, it is cream-yellow. Its color becomes darker as it matures. It has a wing cover and each will have eight black spots.

Yello Mexican Bean Beetle

A Mexican Bean Beetle on a Leaf

Mexican Bean Beetle’s Habitat

The habitat of Mexican bean beetle may change depending on its specific stage of development. The eggs are laid on the undersides of the leaves of the host plants and are usually in clusters of up to 75. Meanwhile, when they are adults, they live under leaves or brushes and they emerge only once the temperature becomes warmer. The lifecycle of a Mexican bean beetle takes an average of 30 to 70 days from egg to an adult, but this will vary greatly depending on the temperature.

Identifying Mexican Bean Beetle’s Damage

Plants Affected

This chewing pest affects a wide variety of beans, which include common beans, tepary beans, lima beans, and soybeans. They are also common in cowpea, legumes, alfalfa, and clover, among others.

Symptoms

Watch out for the following signs so that you will have an idea if Mexican bean beetles are already affecting your plants:

  • The leaves are the ones that will suffer the greatest injury. The larva will cling on the lower surface of the leaf and will chew the edges. You will see irregular sections and holes on the leaf. Eventually, the holes will grow bigger. This causes the leaf to dry and die. Some of them will also fall on the ground and will leave only the skeleton of the host.
  • Although feeding happens primarily on the leaves, they will also damage the pods, flowers, and fruits. Most of the impacts will be evident early on. This can cause cosmetic damages on the fruit. The larva will create entry holes, making the fruit more susceptible to damages, and in the end, can make it unmarketable.

Results of Infestation

Both the larvae and adults will consume the plant tissue of their host. Because of their foliar feeding, the photosynthetic capability of the plant will be affected. With the deprivation of the nutrients that are necessary for survival, overall health will suffer. In most cases, this will lead to a severe case of defoliation. Only the skeleton of the host plant will remain, and eventually, it will also die. Under regular conditions, a lot of varieties will tolerate the damages. However, when the infestation is severe and if you fail to act from early on, the problem can escalate.

Damaged Beans

Unprotected Beans are Devastated by Mexican Bean Beetles

How to Get Rid of Mexican Bean Beetles

Natural and Organic Solutions

Thinking of eliminating this pest in a manner that is safe and organic? The following are some of the solutions that can deliver promising results:

  • Among others, one of the first solutions that you have to try is hand-picking the Mexican bean beetle. It will be best to do this when they are still eggs. When they are already larvae or adults, it might be too late. But still, removing them in mature stage will help to control the infestation. Throw them in a bucket of soapy water. This will make sure that they will die and won’t return to the host plant.
  • The destruction of the locations where they overwinter is another solution that will work, although this is more of a preventive measure. By doing this, you are acting early on. You are destroying the adults before they hatch eggs or the eggs before they hatch the larva. Tilling or pruning are some of the things that you can do, aside from manual removal.
  • Another solution that will work is the introduction of natural predators. This is a biological control that will allow you to kill the pest before they can cause severe damages. There are at least 17 predators that will feed on the eggs of Mexican bean beetles. Some of the perfect examples of the latter include eulophid wasp, stink bugs, and lady beetles.
  • The use of kaolin clay is another method that you should not ignore. Kaolin provides a protective barrier that will help to keep the beetle out.
  • Another non-toxic solution that can prove to be equally effective is the use of diatomaceous earth. It works immediately, killing the beetle upon making contact. Simply dust it on the affected plants and watch it work like magic.

Chemical Solutions

Before resorting to this method, be familiar with the dangers that it can pose. These chemicals can be hazardous even for beneficial insects. To yield the highest level of effectiveness, make sure to cover the plant liberally. Pay attention to the instructions from the manufacturer and always wear safety equipment.

Pyrethroids and neonicotinoids are some of the most popular chemicals today. There are more chemicals used in the 1960s, but manufacturers are no longer offering them because they are toxic and will make the beans inedible. One of the best products you can use is Azatrol EC, which has azadirachtin. It is important to note, however, that using this does not yield immediate results. In most cases, it will take roughly 21 days before it takes effect.

How to Prevent Mexican Bean Beetles

There are various preventive measures that are promising in terms of their effectiveness. Among others, one of the best is the perfect timing of planting. Early spring or late summer are some of the best times, which will help in the mitigation of the population of the Mexican bean beetles. It will also be good to plant crops that can resist the pest, which include Idaho Refugee snap bean and Baby Fordhook lima bean. Lastly, make sure that you maintain the plants in their best condition. Watering and frequent inspection are two of the things that will help. By inspecting the plants often, you will know if beetles are already present, and consequently, you can execute the best course of action for their elimination.

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