Monday, June 24, 2013

Watching casebearer larvae work

Two nuts have been destroyed by a single casebearer larva
    Pecan nut casebearer larvae continue to feed on pecan nut clusters. This morning, we found 5.3% of nut clusters infested with a casebearer larva in untreated plots. The larvae are starting to move into a second nut in the cluster (photo above right).
    If you look carefully at the photo, the full story of how these pecans were destroyed is revealed.  The smaller, brownish nut at the bottom of the photo was attacked first. As soon as this nut was damaged by the casebearer larva, the nut stopped enlarging and began the process of aborting from the tree. By the time this photo was taken, the damaged nut had formed an abscission layer and had separated from the stem.  With great foresight, the casebearer larva wisely attaches the nut to the tree with several strands of white silk. This prevents the nut from falling to the ground and allows the larva to remain in the tree. Since one pecan is not enough to satisfy all nutritional needs of a growing caterpillar, the casebearer larva moved to the lowest nut in the cluster and began tunneling inside. You can tell that the caterpillar had grown larger in size by the time it got to the second nut because the pile of frass (i.e. insect poop) at the base of the nut is larger and more coarse.

    There are times when a casebearer larva never finishes it meal of pecans. In the photo at left, two nut were destroyed by a casebearer. Judging from the size of these damaged pecans, the larva should have attacked the third and final nut in the cluster. However, it looks like an insect predator might have gotten to the casebearer larva before it could attack the third nut. During my survey this morning, I spotted several wheel bugs actively searching the pecan canopies for insect prey. Casebearer for breakfast--what a lucky wheel bug!