The pecan nut casebearer, Acrobasis nuxvorella (Neunzig), is the most damaging nut-feeding insect that occurs in pecans. This species only occurs in pecans but is closely related to similar species that cause the same damage in hickory and walnut. The pecan nut casebearer (PNC) is found from Florida to southern New Mexico, encompassing almost all of the pecan growing region.
Pecan nut casebearer can complete two to three generations per year. Overwintering larvae develop into pupae and ultimately moths that emerge from late May to early June. After tree pollination, female casebearer moths begin laying eggs on pecan nuts. These eggs result in first-generation larvae that feed on pecan nuts and generally cause the most damage.
Second-generation PNC begin appearing in mid-July. Larvae feed primarily on pecan shucks. Unless populations are extremely high, little damage is created from second-generation larvae. Third-generation PNC hatch 30 to 40 days later and feed for a short time (if they feed at all) on shucks. Late in the season, each small larva forms a tightly woven, protective silken case (hibernaculum) near a bud or leaf scar for overwintering. These larvae emerge from hibernacula in the spring and feed by tunneling into shoots. Pupation of the overwintering generation occurs in these tunnels formed from feeding, and adults emerge the following spring to deposit the first generation of eggs on pecan nuts.
Pheromone-baited traps for PNC are available. The pheromone mimics the chemical emitted by female casebearer moths and attracts males to a sticky trap. Traps can be used to detect the arrival of PNC into an orchard, to provide growers an estimate of population numbers, and to provide a signal of when first significant nut entry by larvae may occur.
Some guidelines for using pheromone traps:
First capture of PNC males generally occurs 12 to 16 days before the optimum time for application of insecticides.
Scouting should begin seven to 10 days after the capture of the first PNC moth.
Look for eggs on the nuts using a hand lens to determine the maturity of eggs.
Examine 10 nut clusters per tree across several trees.
If two or more clusters contain eggs or damage before 310 clusters have been examined, an insecticide application should be made as soon as possible.
Traps can be used to monitor flights of later PNC generations.
Second-generation PNC occurs approximately six weeks after the spring flight, and larval damage can be expected 12 to 16 days after the flight begins.
The decision to treat an orchard is based on scouting to detect eggs and/or larvae not on the numbers of moths captured. The traps allow you to know when to start scouting for eggs. The pheromone trap is very effective and will capture moths even when economic infestations of larvae are unlikely to develop. Later generations (third and possibly a fourth) are rarely a significant threat to nut production.