Field Guide     Pest Management     Mexican Bean Beetle

Mexican Bean Beetle

CROPS IMPACTED: lima beans, soybeans, cowpeas, fava beans, mung and lentil beans.

mexican-bean-beetle-1

Family: Coccinellidae

mexican-bean-beetle-2 mexican-bean-beetle-3

About Mexican Bean Beetle

Reproduction and Life Cycle

Mexican Bean beetles overwinter as adult beetles. When spring comes around, the overwintered beetles emerge, eat, mate and lay eggs on the bottom side of leaves. 2 weeks after being laid, the eggs will hatch and larvae will join the adult beetles, eating host plant foliage. Larva will feed for about 1 month after birth before they attach themselves on plants to pupate. 2 weeks after entering the pupation stage adult beetles will emerge. In 1 year there will be 1 to 2 generations of Mexican bean beetles, depending on location and weather conditions.

Mexican Bean Beetle Identification and Habitat

Identification

Eggs of the Mexican bean beetle are bright yellow in colour and are laid in large clusters of 40 to 60 on the leaves closer to the ground. The larva that comes from these eggs are oval shaped, yellow in colour and covered in small black spines. They go through 4 instar/molting stages, have soft-bodies and a fuzzy appearance. After completing all molting stages Mexican bean beetles will pupate, looking similar in appearance to their larva stage, but lighter in colour. The adult Beetles looks similar to a lady bug; their bodies are oval in shape, about 9mm long, copper to orange in colour and have 16 black spots in rows of 6-6-4 along their backs.

Habitat

Mexican bean beetles are less of a problem in hot, dry areas. Both Mexican bean beetle larvae and beetles feed on flowers and pods with most injury occurring on leaves by larva. Feeding occurs by the eating of the entire leaf, leaving behind veins and a “skeletonizing” effect on the leaves. Plants that are attached and eaten in this manner are most commonly legumes such as snap and lima beans, along with soybeans and cowpeas. Plant varieties that are still attached but less desired by Mexican beetles are fava beans, mung and lentil beans.

Mexican Bean Beetle Control Methods

Cultural Control

One of the best cultural control methods is to plant beans as soon as possible; this will allow the beans to become much more established before Mexican bean beetles infest fields. Another control measure is controlling the weeds in and around fields that could be vulnerable to infestation and over-winter sites.

If you are looking to control Mexican bean beetles in gardens or small areas, you can cover crops with floating row covers once they have been planted and until harvest time. Another option is after harvesting beans, pull infested plants and place them into a sealed plastic bag. A week later you will be able to compost the dead beetles and plants. This control strategy may allow the adults to fly away but it will kill any eggs and larva left on the plants.

Chemical Control

If you are looking for protection against early–season feeding, deed treatment insecticides can work well. Foliar insecticides can be used; however, it is strongly recommended to apply it when there is a large infestation due to the fact that these kinds of insecticides will kill wanted bugs. Some chemicals that can be used in these large infections: pyrethrum, spinosad and neem.

Latin / Alternative Mexican Bean Beetle Names

  • - Epilachna varivestis

Sources

http://www.omafra.gov.on.ca/english/crops/pub811/13drybean.htm#mexicanbb

http://extension.umd.edu/growit/insects/mexican-bean-beetle

http://bugguide.net/node/view/8712