Functional response of egg parasitoids, Psix saccharicola and Trissolcus agriope (Hymenoptera: Scelionidae) on cold-stored eggs of Acrosternum arabicum (Hemiptera: Pentatomidae)

Storage at low temperature for host availability at different times is a valuable way to increase the mass production of natural enemies for biological control programs. Usually, host cold storage is done at temperatures below the optimum temperature and can affect the adaptations of natural enemies. Egg parasitoids, Trissolcus agriope and Psix saccharicola from Scelionidae family are as biological control agents against important pest of pistachio, greenstink bug, Acrosternum arabicum. In this study, effect of host egg storage at 4 ± 1 °C on functional response of Trissolcus agriope and Psix saccharicola were evaluated at different densities (5, 10, 15, 20, 25, 30, 35, 50, 65, 80 and 95) under laboratory conditions. Logistic regression analysis revealed a functional response type III for T. agriope on both fresh and cold-stored eggs and type III and II for P. saccharicola on fresh eggs and cold-stored eggs, respectively. Although the type of treatment did not change the type of functional response in T. agriope but were reduced the type of response from III on fresh eggs to type II on cold-stored eggs in P. saccharicola. However handling time in both species were increased in cold-stored eggs treatment compared to fresh eggs treatment. Our results suggest that T. agriope can successfully parasitize cold-stored eggs of A. arabicum without considerable undesirable effects on its parasitism rates. However, this method may have negative effects on the performance of some other parasitoid wasp, including P. saccharicola.