Fuzz on the Kale

Braconid pupae from kale - REK

My editor (wife Barb) keeps me constantly entertained with her discoveries in the garden.  This time it was clusters of tiny fuzzy spots stuck on the underside of lots of our kale leaves.  The whole cluster measured only an eighth of an inch, a jumble of oblong fuzz balls.  We put the leaf fragment in a plastic box and left it on the dining table for a few days.*  

Braconid Wasps - REK

When we next checked it there were tiny 2mm black specks on the lid.  When I opened it, they immediately flew out.  The next day there were more and this time the box went in to the freezer for a few hours before opening it. These turned out to be tiny wasps.

I sent the pictures to Bugguide.net and got a rapid response from Ken Wolgemuth.  He identified them as braconid wasps (Braconidae) in the subfamily Microgastrinae.  He explained that these are "individual cocoons that were spun by the wasp larvae that were consuming the host (e.g. caterpillar) that was feeding on your kale. They then emerged from these cocoons as the adult wasps you are seeing now."

Braconid wasp - 2mm   REK

The Braconidae family of wasps numbers over 17,000 species and counting.  They are parasitic like their larger Ichneumonoidea wasp cousins, using the larvae of beetles, flies, butterflies and even aphids to feed their young.  Once they crawl out, they spin their cocoons for protection until they emerge as adult wasps.

We think of having a virus as a disease but for Braconid wasps polydnaviruses are their nannies.  The wasps carry polydnaviruses which they have coevolved with over thousands of years.  These are injected into a host caterpillar along with their eggs.  The viruses are harmless to the wasp but immediately start to disable the host's immune defenses against the foreign eggs.  The wasp eggs hatch, develop into larvae and feed inside the host until they emerge and form the pupae we found above.  The wasps soon emerge and begin the cycle again with their friendly virus still on board.**

Cabbage white - Bob Moul

These clusters were really good news.  We have lots of cabbage white butterflies (CWB),  Pieris rapae, constantly hovering around the kale.  They are the most common butterfly in North America, an unwelcome European import which arrived around 1860 and is now on every continent on the globe except Antarctica.  They are a hearty breed, the first to emerge in the spring, flying from March through November.  In addition, their reproductive success comes from the fact that they may have 7-8 hatches a year and the wide range of host plants they can raise their young on.

Cabbage white caterpillar - Wikipedia- CC

On close inspections any of you gardeners may find one of these innocent looking caterpillars.  CWB lay one egg on each available leaf of their host plant. They eat predominately plants in the mustard family, (Brassicaceae) including cabbage, broccoli, and our kale as well as dandelion, red clover, asters, and mints.  They seem especially addicted to our leafy garden plants, chewing holes in the kale leaves until they look like  sieves. 

Cabbage white pupa - Bob Moul

The pupae of the cabbage whites are green or brown with points on the ends, resembling a dried up leaf. The last batch of caterpillars hibernate over the winter as chrysalids and hatch into adult butterflies in the spring ready to start the cycle again.  We have learned to embrace these little fuzzy spots on the kale leaves, wishing them great reproductive success as they munch away on the innards of the invasive caterpillars.

We can almost forgive them for occasionally attacking caterpillars we raise at the Butterfly House.  For a graphic example of Brachnoidae larvae emerging from horn worms, check this Youtube video.

*  Note: I am blessed with a wife that will tolerate road kill snakes and a found blue heron skulls in her freezer.  Since she accepts them, what problem is a little plastic Gerber baby food box containing insects sitting beside the salad bowl?
**  Braconid wasps and Polydnavirus