Long-term storage of eggs of Leptoglossus occidentalis for the mass-rearing of its parasitoid Gryon pennsylvanicum

Leptoglossus occidentalis Heidemann (Heteroptera, Coreidae) is a harmful insect to cones and seeds of several conifers in North America, and was accidentally introduced into Europe where it rapidly spread to many countries. In Central Italy, the pest damaged cones and seeds of Pinus pinea L., leading to a severe reduction of pine nut production. Gryon pennsylvanicum (Ashmead) (Hymenoptera, Platygastridae) is the most common egg-parasitoid of L. occidentalis in British Columbia. This natural enemy has been successfully reared under laboratory conditions. However, the possibility to arrange a sufficient large number of specimens is crucial for the success in biological control. In the present work, stored L. occidentalis eggs at fridge and freezing temperatures of +4, −20 °C, and ultra-low temperatures of −80 and −140 °C for different times up to one year, were tested for parasitization success. Results showed that G. pensylvanicum can exploit successfully host eggs stored for long time when stored at ultra-low temperatures and that storage did not affect fitness of the first and second generation. For shorter periods of time, the use of +4 °C for store eggs did not vary significantly from eggs stored at ultra-low temperatures.