Presence of exit hole on the hull of the fruit, about 1 mm in diameter. Fruit are also damaged via the feeding activity of the larvae. It is a pest in many areas of the world where pistachios are grown and has the potential to reduce yields. The species can be introduced into new areas via infested and improperly fumigated seeds or ornamental trees that are also alternate hosts. With this pest it is important to examine nuts for small holes and use yellow sticky traps to monitor adults.
The symptoms are caused by the pistachio seed chalcid (Megastigmus pistaciae), a wasp that has two generations per year. It overwinters as larva in the infested pistachio nuts. In the spring, the larvae transform into adult wasps, which exit the nut by chewing a tiny exit hole (1 mm) through the hard shell. These newly emerged females lay their eggs through the hardening shells of ripening nuts in May and June. The second adult generation emerges in the mid- to late-summer. Some of the larvae actually do not emerge as adults in the same year but remain latent in the nuts until the following spring. These females lay through hard shells of ripe nuts, producing a new batch of overwintering larvae.
Removing all nuts after harvest is an effective way to prevent hibernating larvae to produce adult wasps in the spring.
Always consider an integrated approach with preventive measures and biological treatments if available. Apply insecticides from the onset of adult emergence. Repeated spraying should be done every 7-10 days until harvest, even after the hardening of the hull. Products based on deltamethrin and lambda-cyhalothrin can be used. The efficacy of treatments depends on the timing of application, the adequacy between the volume of the product applied and that of the trees, the use of the recommended dose and the speed of the atomizer.