Controlling Effects Of Intercropping On Wheat Aphids In Diversified Wheat Fields

The English green aphid Macrosiphum avenae is the major pest of wheat in China and many other countries. It is not only as a vector of plant virus diseases, but also making heavily damage to wheat. Garlic Allium sativum and oilseedrape Brassica napus are very important intercropping crops of wheat in huang-huai-hai wheat region. This paper investigated the ecological effects of wheat-oilseed rape or wheat-garlic intercropping and aphid-resistant wheat cultivars intercropped with oilseedrape to M. avenae and its natural enemies. The main results are as follows:1. Effects of wheat-oilseed rape or wheat-garlic intercropping on population dynamics of Macrosiphum avenae and its main natural enemiesIn the study, we intercropped garlic and oilseed rape into wheat to examine ecological effects of this intercropping system on the population dynamics of M. avenae and its main natural enemies. The results showed that the densities of M. avenae apterae were almost significantly lower in wheat-oilseed rape intercropping fields and wheat-garlic intercropping fields than wheat monocultures. There were higher population densities of ladybeetles and higher ratio of ladybeetles to M. avenae in wheat-oilseed rape intercropping fields. The population densities of aphid parasitoids were higher in wheat-oilseed rape intercropping system before May 2. After May 5, the mummy rate and ratio of aphid parasitoids to M. avenae in wheat-oilseed rape intercropping fields were significantly higher than other planting patterns. In wheat-garlic intercropping fields, there were more M. avenae alatae, but no significant change was observed in the population densities of ladybeetles and aphid parasitoids. It was suggested that wheat-oilseed rape or wheat-garlic intercropping could reduce the population densities of M. avenae in agroecosystem. 2. Community dynamics of pests and natural enemies in wheat-oilseed rape or wheat-garlic intercropping fieldsThe dynamics of pests and natural enemies in different intercropping patterns were investigated with biodiversity measures including species richness (S), dominance (D), Shannon's Index (H′), and evenness (E). The results showed that, some influences were observed on pests'index of diversity and evenness in wheat-garlic and wheat-oilseed intercropping systems, but no significant difference was detected on index of species richness and dominance. Diversity index of pests in wheat-garlic intercropping fields was significant higher than wheat-oilseed intercropping fields from April 20 to 26. Evenness of pests influenced by different planting patterns was at late growth stage of wheat. After May 14, pests'index of diversity in wheat-oilseed rape intercropping fields was significantly higher than other planting patterns. Species richness of natural enemies influenced by different planting patterns was at early growth stage of wheat. Before May 2, species richness of natural enemies in wheat-oilseed rape intercropping fields was significantly higher than wheat monocultures and wheat-garlic intercropping fields. There were no significant differences on dominant species of natural enemies among three planting patterns. After May 8, dominance of Aphidius avenae in wheat-oilseed rape intercropping fields was significantly lower than other planting patterns. During investigation, diversity index of natural enemies in wheat-oilseed rape intercropping fields were higher than wheat monocultures and wheat-garlic intercropping fields, and index of evenness were significantly higher in wheat-oilseed rape intercropping fields than other planting patterns after May 8.3. Intercropping aphid-resistant wheat cultivars with oilseed rape on the control effect of wheat aphid (Macrosiphum avenae)The effects of intercropping of wheat cultivars and oilseed rape on the densities of wheat aphid, Macrosiphum avenae, and their arthropod natural enemies were evaluated. Three winter wheat cultivars with different resistant levels to M. avenae were used:'KOK'(high resistance),'Xiaobaidongmai'(low resistance) and'Hongmanghong'(susceptible). The results showed that the densities of M. avenae were significantly higher on the monoculture pattern than on either the 8-2 intercropping pattern (eight rows of wheat with two rows of oilseed rape) or the 8-4 intercropping pattern (eight rows of wheat with four rows of oilseed rape). The mean number of predators and the mummy rates of M. avenae were significantly higher in two intercropping patterns than those in the monoculture pattern. The densities of M. avenae, ladybeetles, and mummy rate of M. avenae were significantly different among different wheat cultivars. The highest densities of M. avenae and ladybeetles were found on wheat cultivar Hongmanghong. The lowest densities of M. avenae associated with high mummy rate of M. avenae were found on wheat cultivar Xiaobaidongmai. The results showed that wheat-oilseed rape intercropping conserved more predators and parasitoids than in wheat monoculture fields, and partial resistance of wheat cultivar Xiaobaidongmai had complementary or even synergistic effects on parasitoid of M. avenae.