HWC GROWS: Beetlemania and the ecology of a rooftop garden


The beetles and their aftermath: damaged bean leaves

A close-up of the beetles

We have an infestation of bean leaf beetles!!! These tiny insects feed on the leaves of beans, creating many small holes that decrease the leaf surface area and impair the plant's ability to convert sunlight into food. They especially like the plant's newest, most tender leaves, which limits the plant's growth and development. I am looking into organic methods of beetle control to save our bean plants.

Because the soil the boxes are filled with came bagged and sterilized, the likelihood of the beetles or their eggs being present in the soil from the beginning is very low. It is amazing to consider how a combination of luck and an acute sense of smell could lead a beetle to find a handful of bean plants that are growing eleven stories above ground level in the middle of a dense urban area.

As I spent some time observing the beetles on the roof, I noticed a number of other insects had found their way to the little garden as well. There were many Asian ladybird beetle larvae crawling around on many of the plants. They feed on other insects, so I am not worried about them harming the plants. I wonder if they might be feeding on the bean leaf beetles.

An Asian lady bird beetle larva sits on an okra stem

I noticed two different wasps that appeared to be hunting on the bean plants. Hopefully they are helping us control the bean leaf beetles! I identified one as the paper wasp and the other is a black wasp that I haven't been able to identify. As I was checking out the developing flower buds of the okra plants, I noticed a metallic blue insect that I think is a cuckoo wasp. It gets its name because it lays its eggs in the nests of other bees and wasps.