The functional response of Aphidius ervi (Haliday)(Hym.: Braconidae, Aphidiinae) to different densities of Sitobion avenae (Fabricius)(Hom.: Aphididae) on two wheat cultivars

The functional response of Aphidius ervi to different Sitobion avenae densities on two wheat cultivars (Sardary and Alvand) was examined in laboratory conditions. Experiments were carried out in test tubes on an F2 lab generation without wheat clusters and also on F2 and F5 generations in pots using wheat clusters. In the tubes, female wasps were exposed to aphid densities of 2, 4, 7, 14, 28, 32, 42 and 56 for one hour, but on the potted plants, to the same densities of aphids for 24 hours. Results obtained from the logistic regression indicated types II (Holling’s model) and III (Roger’s model) in all 3 experiments on Alvand as a resistant cultivar and Sardary as a sensitive cultivar, respectively. The type II model of functional response fitted on data obtained on the Alvand cultivar indicates a negative bottom top impact of the resistant cultivar on the parasitoid. The model parameters estimated for F2 and F5 wasps were not significantly different for the Sardary cultivar. However, the area of discovery and handling time in the F5 generation on the Alvand cultivar were higher than that of F2.