Description:
Copper coloured, oval, 1/4 inch long, 16 black spots on back. Larva: Orange to yellow, fuzzy or spiny, up to 1/3 inch long.
Common Host Plants:
Beans, lima beans.
Damage:
Adults and larvae feed on pods and on underside of leaves; pods and leaves are skeletonized.
Distribution:
In most states east of Rocky Mountains.
Lifecycle:
Mexican bean beetles overwinter as adults on trees, shrubs, or in plant debris. In early spring some adult beetles end their hibernation and begin feeding and throughout the spring more adults will continue to emerge from hibernation. Females lay eggs in yellow-orange clusters of 40 or more on undersides of leaves.
Each female will lay an average of 460 eggs. In 5-14 days larvae emerge, feeding until maturity is reached in about 2-5 weeks. Pupation occurs on leaf surfaces. Adults appear in less than two weeks to begin the cycle again. The time span from egg to adult beetle is about one month and multiple generations occur annually in Virginia.
Thresholds:
If populations on beans are an average of 1/2 a Mexican bean beetle per plant or if there is more than one egg cluster per row foot, treatment is warranted.
Cultural Control:
Clean up plant debris after harvest. Plant Beans as early as possible to so harvest is completed before the July peak of activity for this pest.
Organic/Biological Control:
Natural enemies include several species of assassin bugs and a tiny parasitic wasp, Pediobius foveolatus. Applications of a botanical insecticide may also help reduce Mexican bean beetle populations.
Chemical Control:
Treat with a registered insecticide when damage first appears. For best control also direct sprays to undersides of leaves.
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