Symptoms characterizing infestations with the pistachio seed wasp are the presence of an exit hole 1 to 2 mm in diameter on the fruit and the presence of a single larva per fruit. Kernels can be completely consumed. This pest originates from the Asiatic regions and is actually an indigenous pest of the inedible nuts of an ornamental pistachio (P. chinensis). It is now also widespread in the Mediterranean basin and attack pistachio orchards. The spread of this parasite poses a serious threat to the pistachio industry, since in severe cases, up to 70% of nuts can be destroyed.
The symptoms are caused by the wasp Eurytoma plotnikovi, which is a widespread and important pest of pistachio. Full grown larvae overwinters in mummified fruits left on trees or laying on soil litter. In spring, as soon as the temperature rises, adults emerge digging a hole on the hull and females search for unripe pistachio nuts to lay their eggs (usually a single egg per fruit). The newly hatched larvae feed on the pistachio kernel until all or almost all the seed embryo is consumed and then enter diapause, remaining inside the nut throughout the year. In spring, next year, the cycle starts again. Poor management practices of the infestations greatly influences the spread of E. plotnikovi in pistachio orchards.
So far there is no biological control method against this pest. However, spray trials with Spinosad (a natural insecticide produced by a fungus) have shown good efficacy. Other trials with mineral products (clay, calcium carbonate) or other natural insecticides have shown overall lower efficacy levels than for Spinosad.
Always consider an integrated approach that combines preventive measures with biological treatments, if available. The control strategy for this insect targets adults only. By the end of March, an emergence cage (e.g. a bottle) should be placed in the orchard. This trap contains a large number of contaminated pistachios (at least 50) from the previous year (with insect inside). This allows to monitor the actual emergence of the adults in the orchard. From the onset and for the whole duration of adult flight, sprays with insecticides every 7-10 days until the shell of the fruit hardens. Different active ingredients can be applied alternately: deltamethrin and lambda-cyhalothrin.