Monday, October 27, 2014

Tight green shucks point to pecan weevil attack

     By this date in late October, all northern pecan cultivars and local native pecans have fully ripened and split shuck. But as leaves start to drop, you might notice a few pecans up in the trees that still have bright green shucks that are still tightly bound to the shell. On closer inspection, you might find a hole in the shuck. This hole could be the exit tunnel for a hickory shuckworm moth but if you take your knife and cut away the shuck you might find the hole continues straight through the nut shell (photos at right).  If the hole goes straight into the nut, what you have discovered is the exit hole for a pecan weevil larvae.
    The weevil larvae that developed inside these pecans completely devoured the kernel inside then chewed a hole through the shell and shuck to exit the nut. Once outside the nut weevil larvae drop to the ground, burrow into the soil, and form an underground cell. The larvae will pupate in the soil before emerging as and adult 22 months later (weevils have a two year life cycle).    

    I pulled a nut cluster off a tree because I noticed all three nuts in the cluster had not split shuck (photo at left). At first look, I saw only two of the nuts had weevil exit holes. But what about the third nut?

    Turning the cluster over, I found the third nut was also destroyed by pecan weevil (photo at left). Since a single adult female weevil can lay eggs in 7 to 15 nuts, it seems likely that the larvae in these three nuts originated from the egg laying activities of a single mother. It is also interesting to note that exit holes occur at seemly random locations on each nut. This may mean that once a larva finishes eating all the kernel inside the shell, the closest exit point is always the best.