Here’s the buzz on wasps: Some are ac­tu­ally ben­e­fi­cial

The Palm Beach Post - Residences - - Residences Treasure Coast / North - Jeff Rugg

Ques­tion: I was look­ing for green cab­bage-moth worms on my broccoli and cab­bage plants when I saw one of the cater­pil­lars next to two piles of eggs. (I don’t re­ally know what they were, but they looked like eggs.) They were on both sides of the cater­pil­lar, and they look yel­low and fuzzy or furry.

I didn’t know that cater­pil­lars could have eggs, so maybe they are from some­thing else. But the cater­pil­lar was still in the same spot hours later. What was this? And should I do any­thing about it?

An­swer: Con­grat­u­la­tions for notic­ing some­thing so small. Keep watch­ing — you will see a crazy nat­u­ral pest con­trol. You are not look­ing at eggs; rather, those are the co­coons of the pupa stage of a very small wasp.

The wasp is the par­a­sitoid of the cab­bage worm. A par­a­site stays in a host for a long time, feed­ing from and liv­ing on it, while not killing the host. A par­a­sitoid feeds and lives for a while but even­tu­ally kills the host.

This wasp has no com­mon name, but the zo­o­log­i­cal name is Cote­sia glom­er­ata. It was im­ported to North Amer­ica back in the 1880s to con­trol the cab­bage worm, which eats plants in the cole-crop fam­ily, such as cab­bage, broccoli, Brus­sels sprouts and cauliflower.

When peo­ple hear the word “wasp,” they usu­ally pic­ture some­thing 1 or 2 inches long at the small­est. Most wasps, how­ever, are less than a quar­ter-inch long and harm­less to peo­ple and pets.

The adult stage of Cote­sia glom­er­ata is only about a mil­lime­ter wide and 2 or 3 mm long. The fe­male lays eggs in­side the inch-long cater­pil­lar. In a few days, the new wasps eat the non­vi­tal or­gans and then bore out the sides, leav­ing be­hind the cater­pil­lar to die within a day. They weave a fuzzy co­coon and hatch into adult wasps in about a week.

The fe­male can lay 20 or more eggs in a cater­pil­lar, and she can lay eggs in 15 to 20 cater­pil­lars. The en­tire life cy­cle takes about a month.

Early in the sea­son, there are fewer wasps than cater­pil­lars. But as the sea­son pro­gresses, as many as 75 per­cent of the cater­pil­lars can be in­fested with wasps. Un­for­tu­nately, pes­ti­cide sprays that kill cab­bage worms kill the wasps, too. Look at the bot­tom of the host plant’s leaves and look for the chrysalis of the cab­bage-worm but­ter­fly. If you see some that are brown in­stead of green, you are look­ing at the dam­age caused by an­other par­a­sitoid wasp that kills the pupa in­stead of the cater­pil­lar: Ptero­ma­lus pu­parum.

Mak­ing the story even more in­ter­est­ing: There are other wasps that lay their eggs in the co­coons of the Cote­sia glom­er­ata. They are hy­per­par­a­sitoid wasps that kill the par­a­sitoid wasps.

One prob­lem with the in­tro­duc­tion back in the 1880s was that not much re­search had been done into whether or not the wasp would in­fest na­tive cater­pil­lars. And even if peo­ple had done that re­search, they would prob­a­bly have thought it would be a good idea to kill any cater­pil­lars. Un­for­tu­nately, it does ap­pear that the wasp has low­ered the pop­u­la­tion lev­els of some na­tive but­ter­flies.

The wasps will be so small that you will prob­a­bly think they are gnats when you are out work­ing in your gar­den. If you want, pluck the leaf off and leave it in a safe place in the gar­den so that the wasps can hatch. En­joy your nat­u­ral pest con­trol.

Jeff Rugg is a Cre­ colum­nist.

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