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Mexican Bean Beetle

Closer Look Of The Mexican Bean BeetleUnlike many beetles which eat aphids, scales and other small insects, the quarter inch Mexican bean beetle will attack snap, cow and lima beans, as well as alfalfa and soybeans. Feeding from under the leaf, they chew holes that make the leaf appear skeletonized with a lace-like look (sometimes called ‘window-paning’), often causing the leaf to dry-up and fall off the plant. The beetle has a complete metamorphosis with distinct egg, larval, pupae and adult stages. Occasionally they can also attack the flowers and growing pods of plants, and in large numbers can completely defoliate your bean crop.


Adult

Mexican Bean Beetle AdultAdult Mexican beetles are oval or dome shaped, usually slightly over a _” in size, straw or cream color when young adults, changing to orange-brown and acquiring their distinctive black spots when mature. Gardeners often mistake these beetles for large ladybird beetles (lady bugs), but these guys eat leaves and plants, not other insects as do lady bugs. They usually over-winter in garden debris, emerging in spring when the temperature warms and the beans begin to sprout. Adults are strong fliers and travel considerable distances looking for new bean fields.


Eggs

Mexican Bean Beetle EggsMexican bean beetles are prolific breeders, the females depositing 500 or more eggs on the underside of bean leaves. Hatching in about a week or two, depending upon temperature, the larvae emerge and can be as destructive as adults. The oblong/oval yellow eggs are usually found in clusters of about 50 or so. Generation time from egg to adult is around 30 days. Between two to four generations can exist during the growing season, depending upon location.


Larvae

Mexican Bean Beetle LarvaeNew larvae are bright yellow in color, turning more greenish as they mature. Having voracious appetites, the slow moving _” larvae can cause considerable damage, usually feeding in packs. In tough times, they will cannibalize the eggs but normally feed for several weeks, molting several times. Beetles in the larvae stage are the easiest to control (eradicate). .


Pupa

Mexican Bean Beetle PupaThe larva fastens the tip of the abdomen to the bean plant and emerges from the larval skin, but still remaining somewhat in it. Hanging there for about a week during pupation, the pupa emerge as young cream or straw colored adults. The pupa is yellow, spineless, and of about the size and shape of the adult.


Vegetables That Mexican Bean Beetles Like To Eat

Alfalfa Eggplant Okra Squashes
Bush Beans Kidney Beans Peanuts Various Weeds
Cow Beans Lima Beans Pinto
Clover Navy Beans Soybeans


Control

ToadPlant quick growing beans before Mexican bean beetle numbers climb to destructive populations, July and August being the worst months. Bush beans are less likely to be attacked than pole beans. Use floating row covers to cover your bean plants in the home garden.

Neem oil is said to be effective against the adults, as is carbaryl.

Toads are said to be very fond of Mexican bean beetles.


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