新疆北部棉区作物景观多样性对棉铃虫种群的影响

如何从景观尺度上实现对害虫的科学管理已经成为昆虫生态学的研究热点.利用频振式杀虫灯诱集技术,从2007-2009年在新疆北部棉区16-17个农场近240km2作物范围内,监测和评估棉田周边作物景观对棉铃虫种群的影响.结果表明:农业景观多样化显著地影响棉铃虫种群数量,复杂作物系统中(棉花比例＜50％作物面积)棉铃虫成虫数量明显大于简单作物系统(棉花比例≥50％作物面积；棉铃虫种群数量与景观多样性指数(Simpson's Reciprocal Index)呈正相关；同时棉铃虫成虫与加工番茄、玉米和小麦的比例成正相关,但与棉花比例呈负相关.研究结果为转基因棉花抗性管理提供科学依据,同时农田景观多样性指标可作为修正棉区棉铃虫预测模型的重要指标.

The effect of cropping landscapes on the population dynamics of the cotton bollworm Helicoverpa armigera (Lepidoptera, Noctuidae) in the northern Xinjiang

The influence of diversity in agricultural landscapes on pest abundance remains controversial despite several studies on the subject. For example, the ecological role of crop diversity in determining the source-sink dynamics of populations of polyphagous Heliothis spp. is complex, and varies at field, farm, region and national scales. Recently, the cropping structures within farms in Xinjiang, China, were adjusted due to changes in market conditions. The effects of these rapid changes in cropping structure at the landscape scale on the dynamics of Helicoverpa armigera have, however, not been well studied. This is particularly so for intensive agriculture in isolated oasis ecosystems, such as the irrigated cropping regions within the deserts of northern Xinjiang. The influence of a mosaic landscape on the population dynamics of H.armigera was measured using light traps in 16-17 farms covering 240 km² in 2007-2009. Light traps were placed in clusters on commercial farms which varied in the relative amounts of cotton, tomatoes, sugar beet, corn and wheat that they grew. Moths were collected and identified every morning from the beginning of May to the middle of August in each of the three years of the study. The average number of moths caught each day/ trap and each month/ trap were calculated for individual farms for each year. Farms were classified according to whether they used complex or simple cropping systems. For the purposes of this study, farms wherein the acreage of conventional cotton constituted < 50% of the cropping area were arbitrarily classed as complex, whilst farms where cotton made up >50% of the cropped area were classed as simple (i.e. with a more homogeneous pattern of crops compared to complex farms).There were at least 3 generations of H. armigera per year, and as moth abundance was highest in the 3rd generation, there appeared to be a progressive build up in numbers through the season. The abundance of H. armigera moths was strongly correlated to the complexity of the agricultural landscape which influenced the source-sink dynamics of these pests amongst the different farms. The abundance of moths in complex cropping landscapes was 2-8 times larger than that in simple cropping landscapes. The area of cotton (as a proportion of arable area) within the study region overall was 88% in 2007, 56% in 2008, and 35% in 2009.A consistent difference in Simpson's Reciprocal Index remained between the complex and simple agricultural systems throughout the 3 years. Furthermore, the numbers of moths captured annually per trap was correlated positively with Simpson's reciprocal diversity for three consecutive years. The annual abundance of H. armigera per trap had a positive relationship with the percentage of corn, processing tomato and wheat grown, and a negative relationship with the percentage of conventional cotton grown. Our study demonstrates that complex landscapes, with a variety of alternative plant hosts provided for H. armigera can support larger numbers of moths, compared with simpler (conventional cotton mostly) systems. These findings imply that diverse landscapes could increase the risk of a pest outbreak in non- Bt cropping regions, and delay the evolution of H. armigera resistant to Bt-crops in the Bt-crop belt. This study also suggests that an agricultural diversity index should be used for improving predictive modeling of pest abundance.