Description of the Pest
The pistachio seed chalcid overwinters as a diapausing larva in infested nuts. In spring the larva pupates, and the pupa transforms to an adult that chews a tiny (1 mm) exit hole through the hard nut shell and emerges as the adult wasp. Female wasps lay their eggs in the hardening shells of maturing nuts in May and June, and the second adult generation emerges in mid- to late-summer. Some of the larvae of this generation do not emerge as adults the same year but remain in the nuts as mature larvae until the following spring. Adult female wasps that do emerge in August and September are able to oviposit through the hard shells of mature nuts, producing overwintering larvae.
Damage
Although the seed chalcid is not a pest of commercial plantings of pistachios in California, it does occur throughout the Central Valley and is a pest in other areas of the world where pistachios are grown. Growers should be aware of this insect because it feeds directly on the pistachio nut and has the potential to reduce yields. It has become a serious pest in some areas of California where Pistacia seeds are produced for nursery rootstocks and in ornamental pistachios planted in urban areas.
Management
Examine nuts for small holes that indicate a seed chalcid has emerged from the nut. Adults can also be monitored by the use of yellow sticky traps that are placed in orchards in early August. Control of this pest consists primarily of orchard sanitation: remove and destroy nuts left on the tree following harvest as well as those that have fallen on the ground.