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Bean Leaf Beetle (Cerotoma trifurcate)

Bean leaf beetle, a part of the leaf beetle (Chrysomelidae) family, is majorly found in the United States’ Western and Eastern regions. Of the several plants, they are primarily a pest of soybeans, resulting in their name.

Bean Leaf Beetle

Scientific Classification

  • Family: Chrysomelidae
  • Genus: Cerotoma
  • Scientific name: Cerotoma trifurcata

Physical Description and Identification

Adult

Size: 3.5 – 5.5 mm (0.14 – 0.22 inches)

Color: Most of the bean leaf beetle species has a black head, and yellowish-green body, with four big black spots sitting on their body, alongside markings of the same color on their wings’ outer margins. Some morphs even have yellow or red elytra with our without spots. Right on top of their elytra, one can spot a black triangle that is one of their main characteristic features.

Other Characteristic Features: They have an oval-shaped body with a prominent head visible from the top. In this species, the elytron remains punctated at the posterior end. The male bean leaf beetle species have patches of hair on their forelegs that seems absent in the females.

Cerotoma trifurcate

Larva

The larva has a white, cylindrical-shaped segmented body and a brown head, closely resembling a corn rootworm’s larva. They grow to about 10 mm (0.4 inches) long and feed on the soybean and other plants’ roots and nodule.

Bean Leaf Beetle Larvae

Pupa

The pupa looks white, too, like the larva with a length of 5 mm (0.2 inches) enclosed with the pupal cells or chamber within the soil.

Egg

The orange eggs are lemon-shaped, mostly laid in the soil near the soybean plant’s base.

Bean Leaf Beetle Eggs

Quick Facts

Lifespan1 – 2 months
DistributionEastern and western parts of the United States
HabitatFields especially where soybean, pumpkin, cucumber, green beans, and legumes grow
Common PredatorsBirds, and tachinid flies
Seasons active fromMid-May – September
Host PlantsSoybean, cucumber, squash, pumpkin, legumes, soybeans, green beans
Diet  of larvae and adultsLarvae: Nodules and roots of soybeans
Adults: Undersides of the leaves of their host plants

Identifying the Damage Caused by Them

A heavy infestation could cause severe harm to the leaves and pods. The first and second-generation beetles mostly chew small holes in the soybean leaves, damaging it greatly. As the foliage matures, the beetles lose interest in eating them and consume the pod’s green skin, leaving nothing but a thin membranous tissue around the seeds. Constant feeding often hampers the production of cops significantly. They are even responsible for transmitting the bean pod mottle virus to the beans through feeding.

The larvae mostly thrive on the root nodules and girdle roots and are not known to cause much harm as the adults.

Did You Know

  • Several measures have often been implemented by farmers to get rid of the bean leaf beetles. Some of them include delaying planting dates and spraying insecticides like pyrethroids.
Bean Leaf Beetle Picture

Image Source: bugguide.net, vegedge.umn.edu, m.farms.com, a4.pbase.com, gopetsamerica.com

Bean leaf beetle, a part of the leaf beetle (Chrysomelidae) family, is majorly found in the United States’ Western and Eastern regions. Of the several plants, they are primarily a pest of soybeans, resulting in their name.

Bean Leaf Beetle

Physical Description and Identification

Adult

Size: 3.5 – 5.5 mm (0.14 – 0.22 inches)

Color: Most of the bean leaf beetle species has a black head, and yellowish-green body, with four big black spots sitting on their body, alongside markings of the same color on their wings’ outer margins. Some morphs even have yellow or red elytra with our without spots. Right on top of their elytra, one can spot a black triangle that is one of their main characteristic features.

Other Characteristic Features: They have an oval-shaped body with a prominent head visible from the top. In this species, the elytron remains punctated at the posterior end. The male bean leaf beetle species have patches of hair on their forelegs that seems absent in the females.

Cerotoma trifurcate

Larva

The larva has a white, cylindrical-shaped segmented body and a brown head, closely resembling a corn rootworm’s larva. They grow to about 10 mm (0.4 inches) long and feed on the soybean and other plants’ roots and nodule.

Bean Leaf Beetle Larvae

Pupa

The pupa looks white, too, like the larva with a length of 5 mm (0.2 inches) enclosed with the pupal cells or chamber within the soil.

Egg

The orange eggs are lemon-shaped, mostly laid in the soil near the soybean plant’s base.

Bean Leaf Beetle Eggs

Quick Facts

Lifespan1 – 2 months
DistributionEastern and western parts of the United States
HabitatFields especially where soybean, pumpkin, cucumber, green beans, and legumes grow
Common PredatorsBirds, and tachinid flies
Seasons active fromMid-May – September
Host PlantsSoybean, cucumber, squash, pumpkin, legumes, soybeans, green beans
Diet  of larvae and adultsLarvae: Nodules and roots of soybeans
Adults: Undersides of the leaves of their host plants

Identifying the Damage Caused by Them

A heavy infestation could cause severe harm to the leaves and pods. The first and second-generation beetles mostly chew small holes in the soybean leaves, damaging it greatly. As the foliage matures, the beetles lose interest in eating them and consume the pod’s green skin, leaving nothing but a thin membranous tissue around the seeds. Constant feeding often hampers the production of cops significantly. They are even responsible for transmitting the bean pod mottle virus to the beans through feeding.

The larvae mostly thrive on the root nodules and girdle roots and are not known to cause much harm as the adults.

Did You Know

  • Several measures have often been implemented by farmers to get rid of the bean leaf beetles. Some of them include delaying planting dates and spraying insecticides like pyrethroids.
Bean Leaf Beetle Picture

Image Source: bugguide.net, vegedge.umn.edu, m.farms.com, a4.pbase.com, gopetsamerica.com

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