Mexican Bean Beetles

For some reason I thought all lady bugs were good bugs. Unfortunately, there are a few lady bugs that are very destructive to plants. One of them is the Mexican Bean Beetle.  The adult is a yellow to copper color and has 16 black spots on it.  In the garden right now I have found the larva feeding on leaves but not the adult or the eggs even though I know they are there since I've found the larva. So here are two links to show what those forms look like.

This links shows the adult, larva and pupa stages of Mexican Bean Beetles. This link shows eggs through adult stages of development for the Mexican Bean Beetle.

Good lady bug larva
     You really DO want larva that looks like this in your bed! They look mean and fierce but they are not harmful to humans, only other insects. This lady bug larva is a very beneficial predator since it eats aphids and other bad bugs. You need to be careful not to spray pesticides on them because you don't want to kill them.

Good lady bug larva

Bad lady bug larva ie Mexican Bean Beetle
When the leaves of your beans start getting spots that are skeletonized, look on the undersides of the leaves for what is eating them. Just as with the squash bugs, you need to look on the undersides of all the leaves to find and remove the the bad critters.

Bean leaves that have been eaten

 

More than likely you will find a larval form that looks like this (see picture below). They don't sting which means you can just pick them off by hand if you don't have too many. Be sure and take them home and throw them in the trash at home. Or if you enjoy squishing them, do it on a hard surface.

Just as an FYI.....squishing bugs in loose mulch doesn't always kill them. There is too much give in the mulch. You really need a solid hard surface like a rock or a piece of wood.

Mexican bean beetle larva

If you have a bad infestation you need to be very diligent about spraying insecticidal soap, Azamax or Neem oil on them. Be sure to get the undersides of every leaf and spray way down into the plant so every surface is coated. Even then you will have to pay close attention to keep them under control because it is very hard to get an entire stand of beans sprayed properly.