Effects of Wheat-Maize Intercropping on Population Dynamics of Wheat Aphids and Their Natural Enemies

To study the effects of wheat-maize intercropping on the population dynamics of wheat aphids and their natural enemies, wheat-maize intercropping patterns were divided into four levels: 8:2, 6:2, and 4:2 intercropping, and monoculture wheat. The results showed that as the wheat coverage rate decreased, the quantities of immigrating winged aphids and their natural enemies significantly differed; the population densities of the natural enemies of wheat aphids continuously rose and reached the highest levels in the 4:2 intercropping. During the stable periods, the maximum population density of wheat aphids was the highest in monoculture wheat. With a reduction in the wheat coverage ratio, the maximum population density of wheat aphids showed a decreasing trend. The control imposed by predatory natural enemies in intercropped wheat was higher than that in monoculture wheat; it was strongest in the 8:2 intercropping and the lowest in wheat monoculture. With an increase in the proportion of wheat, the parasitism rate of parasitic wasps increased gradually and reached the highest level in 4:2 intercropping. The effect of host density on hyperparasitism was significant in the intercropped wheat. The intercropping pattern had a great effect on the wheat aphids' natural enemies. In different agricultural landscapes, the diversity of wheat aphids' natural enemies differed significantly between intercropped wheat and monoculture wheat; in the heterogeneous landscape, the natural enemy diversity was highest in intercropped wheat, and it was far higher than that in the other wheat cultivation patterns. The natural enemy diversity was also slightly different between monoculture wheat in the heterogeneous landscape and intercropped wheat in the homogeneous agricultural landscape.