Tritrophic interactions in a wheat (Triticum aestivum), aphid (Rhopalosiphum padi) and parasitoid (Aphidius matricariae) system

The effect of different wheat cultivars (Pishtaz, Pishgam, Parsi, Sivand, Sirvan, Tajan, Zarrin, Alvand, Shahriar and Darya) on the life table parameters of the aphid Rhopalosiphum padi (L.) and its parasitoid Aphidius matricariae Haliday was determined based on the age-stage, two-sex life table theory. All experiments were implemented in a growth chamber at 25 +/- 1 degrees C, 60 +/- 5% RH and a photoperiod of 16 L: 8 D hours. The results revealed that different wheat cultivars significantly affected development time and population parameters of the second (aphid) and third (parasitoid) trophic levels in a tritophic system. The shortest development time of R. padi was observed on both Pishgam (5.00 +/- 0.13 d) and Alvand (5.03 +/- 0.08 d). The longest development time was obtained on Shahriar (7.98 +/- 0.21 d). The highest values of population growth parameters of R. padi were obtained on the Pishgam and Alvand cultivars, showing high susceptibility of these cultivars to the R. padi infestation. The tritrophic experiments conducted on the cultivars Shahriar and Pishgam revealed that A. matricariae parasitized more aphids on Pishgam and allocated higher intrinsic rate of increase on this cultivar compared with the resistant one. Regardless of the resistance pattern, the highest age-stage parasitism rate of A. matricariae on R. padi occurred on the first day of oviposition. However, the life history traits of R. padi and A matricariae both decreased on the resistant cultivar, and, as this reduction was less in the parasitoid wasp, the combination of a resistant wheat cultivar and A. matricariae have potential for controlling R. path in an IPM program, though additional field trials are needed to confirm this.