The Mexican bean beetle looks an awful lot like a ladybug of a different color, and we all love ladybugs, or as some call them, ladybirds. But under that cute orangish exterior lies a voracious agricultural pest. Unlike its sweet red relatives, it doesn’t prey on other pest insects, but on the plants themselves. How can you avoid this hungry spotted bean beetle? Let me help!
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|Common Name(s)||Mexican bean beetle|
|Scientific Name(s)||Epilachna varivestis|
|Origin||Mexico & the United States|
|Plants Affected||Common beans, lima bean, mung bean, thicket bean, soybean, adzuki bean, cowpeas, alfalfa, & some clovers|
|Common Remedies||Hand-picking beetles, insecticidal soaps, neem oil, pyrethrin or azadirachtin sprays, diatomaceous earth, kaolin clay, beneficial insects (ladybugs, lacewings, minute pirate bugs, spined soldier bugs), floating row covers|
Epilachna varivestis is one of the rare lady beetles that feeds on plants instead of other pests. It is on occasion referred to as the bean ladybird. However, you compare the Mexican bean beetle vs ladybug, it’s easy to tell which is a pest and which is a beneficial garden dweller.
Its color varies, making it hard to distinguish at times from the ladybug, but at other times quite easy to identify. Typically, it is found in shades of bright yellow to rusty brown. It can sometimes be bright orangish-red. The bean beetle has eight dark black spots on each of its elytron, the hardened upper forewings that appear to cover its back when it’s at rest.
Mexican Bean Beetle Life Cycle
In the late spring, Mexican bean beetle adults emerge from their dormant overwintering state. The females begin to lay eggs in groups of 50-75 on the undersides of leaves.
The larvae feed rapidly throughout a field as they hatch, laying waste to your crops. This period is when the worst damage occurs. As they grow, they pass through four moulting cycles, shedding their prior skin to allow for further growth. Once they are at their full larval size, they will attach themselves to the underside of a leaf and pupate there. This entire cycle takes 3-5 weeks.
Once they emerge from the pupa, the adult can begin the life cycle once more. When the weather becomes cold in the late fall, they will retreat into the shelter of local woodlands or hide in plant refuse for the winter.
As the name suggests, it lives throughout Mexico and can be found through the eastern United States. It also flourishes in the irrigated croplands west of the Rocky Mountains. Like most pests, they go where their food supply is most abundant.
They can be found during the spring, summer, and early fall months. The most destructive time of year for these Mexican beetles is the summer. They then retreat to a sheltered location in nearby woodlands or under nearby plant debris for the winter.
What Do They Eat?
True to their name, they’re quite fond of bean leaves and bean pods. They will eat common beans, lima bean, mung bean, thicket bean, soybean, adzuki bean, cowpeas, alfalfa, and some clovers. When they eat, they tend to skeletonize leaves, leaving visible damage behind. This makes it a bit easier to notice the danger lurking under the foliage and take steps to eliminate the bean beetles.
How To Get Rid Of Mexican Bean Beetles
So now that you know all about them, let’s go over ways to wipe these pesky Mexican insects out of your yard.
Your first stage of defense is to literally pick the bugs off of your plants. Using your fingers or a pair of tweezers, pluck the adult and larval stages off of leaves and drop them into a bucket of hot soapy water. This prevents the adults from flying away and will kill the pests. You can also use a flat item such as the back of a butterknife or the side of a trowel to scrape eggs off the back of leaves if you discover a widespread collection. It’s easier to just trim off colonized leaves and destroy them entirely.
Use diatomaceous earth to not only deter egg-laying, but to kill the beetles. Their soft undersides are no match to the sharp edges of the superfine crystalline powder. Food-grade diatomaceous earth is completely safe to both humans and pets, but to insects, it’s like thousands of tiny razor blades.
Spot treatments with insecticidal soaps such as Safer Soap are good. If you’re seeing limited quantities of bean beetles in your yard, this should help to wipe out what’s there and discourage a longer stay. However, you’ll need to thoroughly coat both the top and bottom of the leaves as well as the plant stems to make this effective.
Neem oil can also be an effective means of control. While this is less likely to kill adults, it does deter them from laying eggs on leaves coated in it, and it will slowly poison bean beetle larva. It’s even more effective when blended with an insecticidal soap like Safer Soap. Neem oil also helps with infestations of other sorts such as aphids and leafhoppers.
Another option is to use pyrethrins. Your first choice should be Safer Brand Yard & Garden Spray, which contains a blend of potassium salts of fatty acids and pyrethrins. It works against a number of pests including cabbage worms, spider mites, cabbage loopers, and many more.
If that doesn’t work, opt for a stronger pyrethrin spray such as PyGanic. Follow the manufacturer’s directions for dealing with a heavy infestation, and you should be rewarded with a bunch of dead adult and larval bugs.
Finally, consider an azadirachtin spray such as Azatrol EC. Azadirachtin is the active ingredient that makes neem oil so effective, but in this case it’s much more concentrated. This will effectively poison both adult and larval stages as well as destroy the eggs. It will also deter future infiltration by the Mexican beetle.
You might think it’s odd to use a ladybug to control a relative of the ladybug. However, in this particular instance, it works quite well. Ladybugs prey on insect eggs, and they’re not picky. Whether it’s aphids and their eggs, yellow eggs of the bean beetle, or any other insect, they will consume them. These beneficial insects truly will help with most other forms of pests.
Another beneficial insect that’s great is the lacewing. These little green bugs will be quite pleased to help gobble up your bean beetle eggs and larvae, and they don’t harm anything in your garden.
The minute pirate bug can also be a great beneficial insect to convince to stay in your garden. These will help keep your leafhopper pest population down while still killing off your Mexican beetle pests.
Spined soldier bugs are also great beneficial insects, and they too love to eat all sorts of pests, from the egg clusters all the way through the adult stage. They can also help you out with your potato bug or cutworm infestations.
Keep your beds clear of plant debris from the fall throughout the winter. Debris, fallen leaves, and the like make an excellent shelter for overwintering bean beetles. By keeping the area clear, you don’t have long-term unwanted guests.
Planting early maturing bean varieties may be one way to reduce the destruction of these pests. While the Mexican bugs are present in the earlier months, they’re still just coming out of hibernation. An early maturing variety may be well-established and able to handle the damage prior to bean beetle infestation. Also, bush beans are more resistant than pole beans. If you opt to plant bush beans instead, you may be able to reduce the population simply from that.
Using floating row covers, such as Harvest-Guard, can help keep all sorts of pests away from your plants. In addition to Mexican beetles, the row covers can keep other beetle species at bay. Cucumber beetles, asparagus beetles and flea beetles are deterred using this method. It’ll also help you prevent a number of other moth larvae like the armyworm or the tomato hornworm.
Apply a light dusting of kaolin clay, commercially sold as Surround WP. This superfine clay forms a waxy coating over the surface of leaves, deterring pests from eating them or laying eggs on them.
Opt to grow companion plants, such as rosemary or marigold. These plants can help to keep the pests from colonizing your yard initially. Other plants which may work well for this purpose are nasturtium or summer savory.
Frequently Asked Questions
Q: How can you tell the difference between the adult beetles and ladybugs?
A: Typically, Mexican bean beetle colors are orange to copper, with the same basic pattern of eight spots per forewing.
Ladybugs tend towards red, red-orange, or red-brown normally in the commercially-available varieties. Some related species of ladybug can be tan or greyish. A few have a lot of spots (up to 15), where others have very few to no spots. However, they all are very similar in appearance.
When you find an orangish-red “ladybug”, look closely at the wings. If it has the same eight-spotted pattern on both forewings, get rid of it, it’s a Mexican bean beetle! Provided that it doesn’t have spots, or the spots appear random, you have a ladybug and it’s perfectly safe.
Q: Are there any other beetles that will eat beans?
A: There is another pest that has the common name of bean beetle. The southern cowpea weevil is actually another beetle species, Callosobruchus maculatus. You will easily be able to tell the two apart, as the southern cowpea weevil is a flattish beetle that tends to be brownish black in coloration. They also cause different types of damage. While the bean beetle will leave skeletonized leaves on your plant, the southern cowpea weevil tends to go after the beans themselves. Both are bad agricultural pests, but we’ll leave the topic of the cowpea weevil until another day!
So, while they’re surprisingly cute, these destructive bean beetles have got to go. Have you encountered this pest in your garden, and if so, did you try any of the techniques I’ve described today? Tell me in the comments below!