Thursday, October 10, 2013

Hickory shuckworm: The worm in the shuck.

   At this time of year, the shucks on many pecan cultivars are starting to split open. Like every over-anxious nut grower, I can hardly wait  to see whats inside the the shuck so I pull a pecan from the tree and peel off the shuck.
    In pulling off the shuck, many times I find an area of blackened tunnels carved into the shuck (photo at right). These tunnels in the shuck were created by an insect called the hickory shuckworm.
    If you carefully tear away the shuck you can often find the small white caterpillar with a red head that had created the tunnels (photo at left). Even though this insect can tunnel a large portion of the shuck , the early ripening nature of our northern pecan cultivars means kernel filling is largely completed before tunneling becomes extensive. This means late season hickory shuckworm feeding does not pose a serious economic threat in our area.
   If hickory shuckworm causes any damage it is usually superficial discoloration on the outside of the shell (photo at right). However, when pecans are mechanically harvested, the constant tumbling inside the equipment usually rubs off all shell markings including shuckworm discoloration.
    Once the shuckworm larva reaches maturity, the caterpillar carves a trap door in the shuck (large black spot on shuck at left). The larva then pupates right under the trap door. Once the pupae matures, an adult hickory shuckworm moth emerges from the pupal case and the moth exits the shuck through the pre-made trap door.
    The adult hickory shuckworm is a small (3/16") dark moth that has an elongated bell shape when at rest (photo at right). Hickory shuckworm moths are largely nocturnal and you rarely see them during daylight hours. I found this moth resting on the shuck just after it had emerged from the shuck.