Lady Beetles (Mexican Bean Beetles or Colorado Potato Beetles)

Lady Beetles or Ladybugs (Mexican Bean Beetles or Colorado Potato Beetles) which one is it?

Lady Beetles -The most common beneficial insect, of course, is the lady beetle that has about 450 species in the US alone. Most people know what a lady beetle looks like and, at some point, have seen one in their homes or outside in the yard. Some key similarities that exist between the lady-bugs in the garden and a major pest that devours your beans, like the Mexican bean beetle, or your potatoes, like the Colorado potato beetle.

Adult Stage of Lady Beetles

The lady beetle larva and adults eat mostly aphids, but they also eat scales, mites, thrips and mealy bugs. The adult hibernates over the winter under logs, leaves and other protective areas. Those seen around the home were imported to control scale such as the Halloween ladybug. This lady beetle which was introduced some years back; it is orange with seven black spots and also can be all black. This particular species has a tendency to group together and look for shelter in homes before the winter sets, invading houses by the thousands. You can easily vacuum them and put the whole vacuum bag outside in a shed near your garden.

Adult lady beetles vary in color from orange, to yellow, pink, tan and white, with black spots on each of their wings, and others are entirely black, brown or grey. They grow between 5/32 of an inch to 9/32 of an inch long.

Mexican Bean Beetle 

The Mexican bean beetle adult is light brown or orange-brown with a bronze tint and has sixteen black spots on the wing covers. They grow to be about 1/3 inch long. The Mexican bean beetles are vegetarians, unlike their cousins that are carnivores, and consume all different types of beans.

The Colorado potato beetle has ten alternating stripped bands of black and light yellow to tan on their wing covers.  The head is tan-yellow with black spot all around.  They grow to about 3/8 inch in length. Colorado potato beetle are also vegetarians that eat potatoes (their favorite plant), peppers, eggplant and tomatoes.

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The Larva Stage

The biggest distinctions is between the larvae stages of each one: The ladybug has a segmented body that is black, long (at their maximum development 3/8”) with black spikes protruding throughout the body and red, orange or black stripes or markings.

The Mexican bean beetle larvae are bright yellow with short spikes protruding throughout its body, like a porcupine, and are oval and chubby. At maturity they are about 1/3 inch long. The Mexican bean beetle larvae cause the greatest damage to plants. They consume the underside of the leaves leaving a skeleton look that causes the leaves to die. Crushing the larva is the best solution- or the eggs, provided you readily see the other stages of the Mexican bean beetle around the plant and know you are not killing a lady beetle.

The Colorado potato beetle has a salmon-pink larvae with black spots along the side, a soft glistening look, humped-backed and approximately ½” long. The larvae feeds on the leaves of their host plants.

Egg Stage

Now we come to the eggs. I doubt that they are distinguishable to the average person. They are all very similar in shape and color, ranging from yellow, cream-yellow to orange in color. The lady beetle will lay eggs wherever there is food for the young larva to feed on. The adults can lay anywhere from 20 to 1,000 in a given season, from spring to summer. The eggs of the lady beetle tend to be slightly smaller (about 1/25” long) than those of the Mexican bean beetle or Colorado potato beetle.

The Mexican bean beetle has a yellow orange tint to their eggs while the ladybug is a brighter yellow or yellow with a tint of red. Mexican bean beetles can lay from a mass of 40 to 75 eggs in one sitting.  They always lay their eggs on the plant they are feeding on- the beans.

The Colorado potato beetle eggs are orange-yellow also lay in mass or small clusters on the underside of the leaves.

Encouraging Lady Beetles to Stay in Your Garden

They have to have food in order for them to stay. The adult lady beetle needs about fifty aphids per day to feed on in order for them to lay eggs. The seven spotted lady beetle can consume 200 eggs and their larva around 300 hundred aphids in order to develop. If you have an abundance of aphids it may be worth the expense to buy some ladybugs. Keep in mind that, once the aphids have consumed all their prey, they will move on to the next garden. The adults will feed on pollen, nectar and sweet water. Therefore, having flowers around the garden, like alyssum, yarrow, marigold, nasturtium, coreopsis, fennel and dill, will help them stay around longer.

Controlling Mexican Bean Beetles and Colorado Potato Beetles

As mentioned earlier, if your garden is small enough, crushing them is the best solution.

• Inspect plants three to four times a week under the leaves where they deposit eggs and develop. 
• Rotate your crops. This way, when the adults emerge, they don’t find the food ready for them to eat but rather a whole different crop, thus forcing them to travel out of the area to eat.
• Encourage lady beetles to stay around; lacewings, parasitic wasp and spiders all help in controlling these pest.
• Plant different varieties than those used commercially.
• Use a seasonal row cover or fabric covers; for more information see my blog on “Season Extenders Comes in all Sizes”. In the case of potatoes, they are self-pollinating and you can keep the cover on all season.
• Colorado potato beetles are difficult to control, even commercially, as they have become immune to all different insecticides- even DDT.  Therefore, hand pick them and crush them.  Plant a commercial variety of eggplant, one that is most common. The eggplant will serve as a trap crop and draw the Colorado potato beetle in ways that will amaze you.

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