Aw, Nuts!

Jan 7, 2009

Walnuts are packed with vitamins, minerals and antioxidants, right?


And sometimes a little protein.

Protein, as in larvae. That's not a welcome sight.

Sometimes you'll find two or three navel orangeworm (NOW) larvae inside a single walnut, along with copious amounts of webbing and frass.

We once stored a bucket of untreated walnuts inside a vacant outbuilding. By spring, we had larvae crawling up the walls and moths trying to find an opening and us trying to find our sanity.

Last weekend I  went on The Great Navel Orangeworm Search. I collected three walnuts that had fallen onto the sidewalk. Two of the walnuts were perfect. Drats!

Ah, but when I cracked open the third, I spotted the larvae.

Three larvae inside the third walnut on the third of January at 3 o'clock in the afternoon.

UC Davis entomology professor Frank Zalom said the best way to tell if the larvae are navel orangeworm is "to check for the presence of a crescent-shaped marking on the sides of the second segment behind the head."

The larva of the codling moth doesn't have this marking.

NOW is no friend of walnut growers. The moths deposit their eggs inside the mummy nuts--the ones left on the trees after a harvest--or the fallen nuts.  Next season: more trouble. Economic trouble.

A pest of both fruits and nuts, NOW was first found in navel oranges; thus the name.

As for the three larvae I found inside the walnut, as soon as I split the hull, they were off and running.

Or rather, off and crawling.

By Kathy Keatley Garvey
Author - Communications specialist

Attached Images:

LARVAE INSIDE WALNUT--This fallen walnut contained three larvae. (Photo by Kathy Keatley Garvey)

Larvae Inside Walnut

IN A NUTSHELL!--Close-up of larva inside a walnut. You can tell if it's a navel orangeworm (NOW) if it has a crescent-shaped marking on the sides of the second segment behind the head, says UC Davis entomologist Frank Zalom. Often, with NOW, there are two or more larvae inside a single nut. (Photo by Kathy Keatley Garvey)

In a Nutshell