Effect of Three Wheat Cultivars on Functional Response‏ ‏of Hippodamia Variegata (col.: Coccinellidae) to the Greenbug, ‎ Schizaphis Graminum (hem.: Aphididae)‎

Different cultivars of a host plant can have an important effect on the behavioral charectristics of natural enemies. In this ‎study, the effect of three wheat cultivars (Ehsan, Morvarid, and Tirgan) on functional responses of 4th instar larvae and adult ‎males and females of Hippodamia variegata Goeze on different‏ ‏densities (2, 4, 8, 16, 24, 32, 64, 96, 128, and 160) of 4-d-old ‎nymphs of Schizaphis graminum Rondani‏ ‏was studied. The experiments were conducted at 25±2 ˚C, 65±5% RH and 16L:8D h ‎photoperiod. The logistic regression analyses revealed that the functional responses of different growth stages of H. variegata ‎to S. graminum on differen wheat cultivars were type II. According to the results, the highest attack rate was estimated for 4th ‎instar larvae of H. variegata on Ehsan and Tirgan cultivars (0.152 and 0.154 h-1, respectively). Also, the lowest handling time ‎‎(0.127 h) was valued for 4th instar larvae on Ehsan cultivar. The predation rate of 4th instar larvae of H. variegata was also ‎highest on Ehsan cultivar. The results of this study revealed the high efficiency of 4th instar larvae of H. variegata in feeding ‎on S. graminum on Ehsan cultivar followed by Tigasn and Morvarid cultivars. Similar results were obtained for adult femles ‎and males of the predator. However, further studies are necessary to evaluate the effect of these cultivars on searching ‎bahavior and consumption rate of different stages of H. variegata on S. graminum under natural conditions. ‎