Patch and prey utilization behaviors by Aphelinus albipodus and Diaeretiella rapae (Hymenoptera: Aphelinidae and Aphidiidae) on Russian wheat aphid (Homoptera: Aphididae)

The patch and host utilization behaviors of the parasitoids Diaeretiella rapae (Kurdjumov) and Aphelinus albipodus (Hayat and Fatima) in relation to the Russian wheat aphid, Diuraphis noxia (Mordvilko), were examined on wheat plants. Individual female parasitoids were observed for 1 h after arriving on a wheat plant with varying D. noxia densities. The total amount of time spent on the leaf and the number of occasions a parasitoid left the leaf were dependent on aphid densities for D. rapae. In contrast, A. albipodus remained on a plant for almost the entire hour irrespective of aphid densities. After 1 h on the wheat plants, single D. rapae females produced up to 31 progeny from 40 aphids, while single A. albipodus produced a maximum of six progeny. These results can be explained by the differences between the parasitoids in prey handling times, searching, and host feeding behaviors, and parasitoid physiology. The mean oviposition time for A. albipodus was 119 s compared to 1 or 2 s for D. rapae. The time between attacks was also much greater for A. albipodus at all prey densities, partially a result of this parasitoid feeding on aphids. Our results agree with the observation that A. albipodus has many fewer eggs ready for oviposition compared to D. rapae. Therefore, it is not surprising that A. albipodus remained for extended periods on wheat plants with many aphids, allowing development of additional eggs and parasitization of more aphids. The patch and prey utilization rates by A. albipodus seem likely to limit its rate of spatial spread during a growing season relative to D. rapae.