Scientific Name: (Epilachna varivestis)
The Mexican bean beetle belongs to the family of highly beneficial and economically important insects, i.e., Coccinellidae, ladybird beetles also share the same profile and pedigree. Two species in the family are considered highly destructive pests, while the Mexican bean beetle is one of them besides the Squash lady beetle. The Mexican bean beetles are so destructive that their larvae and adults both feed on the upper foliage of the bean plants instead of predating the aphids, whiteflies, thrips, scale insects, and other soft-bodied pests. The Mexican bean battles are widespread pests in Mexico and the eastern US, in the areas of higher rainfall and humidity, and limited in exceptionally-dry regions. The Mexican bean beetle overcomes the whole culture of beans, whether they grow in a corporate sector or home gardening.
Origin and Distribution
The Mexican bean beetle is a North American ladybird that hails from the southern Mexican plateau region and dominates in most areas of the east of the Rocky Mountains. The Mexican beetle is prevalent in beans growing areas of the eastern regions whereas, they're limited to isolated areas in western regions which primarily depends on rainfall and local growing conditions. The beetles southern limit extends to Guatemala and northern up to New England and southern Canada. The Mexican bean beetle invaded Florida in 1933 and 1938 and established itself in 1942. The Mexican bean beetle is an established garden and commercial beans pest throughout Mexico, and the eastern US in the areas of higher precipitation, and humidity together. They may be present on all 400 species of beans and most widespread on Red beans, Anasazi beans, Mung beans, Chickpea, Black-eyed beans, Soybeans, Lentils, Black beans, Kidney beans, Lima, and Fava beans.
Mexican Bean Beetle- Identification
The Mexican bean beetle eggs are light yellow to orange-yellow that may be found on the undersides of the leaves in the clusters of 40 to 75. Newly-hatched larvae are light yellow and measure about 1.6 mm long. Their bodies remain covered with branched spines in longitudinal rows on the back. The larvae have a fleshy body that tapers on the posterior end to an anal segment having an apparatus that attaches them to the surface of the leaves. Mature larvae may measure about 5.0 to 7 mm long, and greenish-yellow. The larvae pupate is attached to the surfaces of the leaves, where they achieve the body size of an adult beetle and remain yellow. The adults are oval and look similar to adult lady beetles having 8-black dots on the sides of the elytron. The adults' color varies in different habitats, whereas the size remains between 6 to 7 mm long.
Mexican Bean Beetle- Lifecycle
The adults emerge from the overwintering sites in early or late summer and start feeding on their favorite host plants. They oviposit on the undersides of the bean leaves after successfully feeding for a week or two. Each female could deposit about 600 eggs in the cluster of 40 to 75. The eggs remain firmly attached beneath the bean leaves and hatch in a week or two depending on the surrounding temperature. The larvae feed collectively for the next five weeks. Pupation takes place in five to ten days while they remain hanging on the undersides of the bean leaves. The adults that emerge after pupation are good flyers, and they can travel long in search of host plants. Adult beetles overwinter in humid and sheltered sites until late spring.
Symptoms and Types of Damages
The Mexican bean beetles' larvae and adults feed on the foliage, floral parts, and bean pods but, the maximum damage is offered to leaves, whereas 3rd and 4th instar larvae cause more damage than the adults. The larvae and adults feed adhering beneath the bean leaves by chewing irregular holes. This injury dries the upper surfaces of the leaves, and the injured leaves offer a skeletonized look. Adults also secrete a distinctive lacy fluid on the foliage. After heavy feeding, the remaining leaves may fall due to rain or wind. The larvae and adults also attack blossoms and small pods in summer and could destroy the entire crop or bean plants in a garden.
Where Do the Mexican Bean Beetle come from?
The Mexican bean beetles emerge from the overwintering locations in late spring to mid-summer when the daytime temperature ranges between 77 to 85°F, and rainfall is usually high. It's time to look them on the undersides of the leaves, where you could find skeletonized leaves in the upper foliage of the bean plants. The Mexican bean beetles prefer to infest lima and fava beans in spring and other early planted varieties.
How to Prevent Mexican Bean Beetle?
Besides all preventive measures if Mexican Bean Beetle infests your garden beans, here are the most proven ways to suppress their population using the biological, organic, and chemical methodologies;
Mexican Bean Beetle- Control
Biological Control
Nature's Good Guys- 500 Orius insidiosus
Orius insidiosus is also called minute pirate bugs, and they are the predators of a wide variety of soft-bodied insects, including the eggs and larvae of Mexican bean beetles. Orius insidiosus multiplies on the plants' tissues and takes almost three weeks to develop from the eggs to adults. They may have several generations in a year. They are readily attracted to the flowering plants where they feed on eggs and larvae together. They insert their long beak into the victim's body and suck body juices leaving only the skeleton. They are voracious eaters and reach where the beetles’ larvae exist.
- Great enemies to all stages of thrips!
- Enemies to aphids, thrips, whiteflies, mealybugs, mites, scale and other soft body slow moving insects
- Can be used indoors and outdoors!
An individual Orius insidiosus bug can eat about 80 eggs or larvae per day.
Southern Ag- Thuricide Bt
Thuricide holds 98.35% sustainable spores of Bacillus thuringiensis-Kurstaki, and each milligram of concentrate contains about 6 million lively spores that produce active toxins in the body of targeted pests. Bacillus thuringiensis are soil-dwelling, gram-positive bacteria that yield crystal proteins that bind with the mid-gut of larvae and adults of Mexican bean beetles and rupture them. It also parasitizes the moths of several other pest species that harm crops. Bacillus thuringiensis is also a component of GMO crops such as Bt cotton and Bt corn that contains the crystal proteins called Bt delta-endotoxin. Thuricide is OMRI listed and can be used on all species of beans that harbor Mexican bean beetles.
- Size: 16 OZ
- Thuricide BT Caterpillar Control concentrate is used by organic gardeners and is made from bacteria that is toxic to listed pests.
- Safe to use on all plants, vegetables and edible crops.
Add 4-teaspoons of the product concentrate per gallon of water, and spray on the beans foliage thoroughly.
Organic Control
Safer- Diatomaceous Earth
Safer- (DE) consists of crinkled fossilized diatoms that have razor-like edges that harm larvae chitin and dehydrate them within 24 hours of application. DE remains soft for humans and leaves no residues in the environment. It also harms larvae and adults when ingested for it quickly absorbs the body moisture that kills them through internal dehydration. DE remains effective until it's dry and needs reapplication after a rain. Since DE kills physically, there are no chances for the pests to develop resistance against it.
- SAY GOODBYE TO BUGS: Kill a wide range of crawling insects like roaches, ants, fleas, silverfish, and bedbugs with our indoor bug and roach killer for insect control
- DEHYDRATES AND KILLS: Our diatomaceous earth, combined with selected bait, causes bed bugs and roaches to dehydrate and die within 48 hours after contact
- VERSATILE APPLICATION: Suitable for indoor and outdoor use, apply our killer for roaches in cracks, crevices and along baseboards inside your home for thorough pest control
Dust DE powder around bean beds and sprinkle on the bean foliage to avoid higher infestation.
Safer- Neem Oil Concentrate
Safer- Neem Concentrate contains 70% Clarified Hydrophobic extract of neem oil that possesses multiple modes of action while controlling different insect pests. Neem Oil contains Azadirachtin which is an insecticide, acaricide, fungicide, and an IGR together. It does not only kill the larval and adult Mexican bean beetles but, somehow suppresses egg hatching and deters the larval feeding. Neem oil is recommended in organic gardening and is often the top choice of indoor commercial growers. Neem oil can be applied to all species and strains of beans irrespective of the growing culture.
- MULTI-USE SPRAY: This Safer Garden Neem Oil is a 3-in-1 spray that works as a fungicide, miticide, and insecticide to eliminate pests and diseases on your favorite plants
- CONTROLS PLANT DISEASES: This Neem Oil spray can be used to prevent and control fungal diseases including black spot, powdery mildew, rust, anthracnose, botrytis, and scab
- KILLS ALL INSECT STAGES: This spray can be used to eliminate eggs, larvae, and adult mites and insects including aphids, beetles, spider mites, whiteflies, and more
Add one ounce per gallon of water and apply on beans foliage in the evening.
Chemical Control
Monterey- Garden Insect Spray, Insecticide & Pesticide
The Garden Insect Spray is 0.5% Spinosad which is a derivative of Saccharopolyspora Spinosa fermentation and holds a fast mode of action. Spinosad contains both Spinosyn A and Spinosyn D, and it got organic status in 2003 by USDA- National Organic Program. Particularly this formulation is OMRI listed and kills Mexican bean beetles during larval and adult stages. Spinosad is not associated with creating any harm for the environment or leaving residues that affect pollinators.
- Fast acting and odorless - Monterey insect Killer is a bacterial product produced by fermentation which rapidly treats plants and does not produce odors.
- Controls many insects - the insect treatment Spray controls caterpillars, leafminers, codling moth, tent caterpillars, gypsy moth, trips, borers, fire ants, and more.
- Variety of uses - this pest control can be used on outdoor ornamentals, lawns, vegetables, and also broadleaf weeds.
Depending on the types of infestations, mix 1 to 2 ounces of the product concentrate per gallon of water and apply to the foliage of the plants from late spring to mid-summer.
Check out our other guides on common garden bugs.