刈割对苜蓿人工草地昆虫群落结构及动态的影响

Cutting effects on the insect community structure and dynamics of alfalfa pasture

运用物种丰富度 (S)、个体数量 (N)、申农指数 (Shannon' s index,H′)、均匀度指数 (E)作为多样性分析的综合指标 ,分析了不同刈割次数苜蓿人工草地昆虫的群落结构和季节动态。结果表明 ,刈割对群落物种丰富度的影响主要是部分稀有害虫种类 ,对优势种和常见种的影响较小。随着刈割次数的增加 ,害虫的物种丰富度下降。刈割对天敌的种类及数量影响较小 ,其影响主要发生在刈割初期。苜蓿人工草地昆虫各类群落的多样性和均匀度指标在时间过程中的变化呈明显的差异和规律性 ,且受刈割次数的影响较大。当 6月上旬苜蓿进入现蕾末期和开花初期时 ,正值害虫始盛期 ,蚜虫、蓟马、盲蝽等优势类群的虫口数量很大 ,总群落和害虫亚群落的多样性和均匀度均很低 ,此时刈割 ,可以有效地降低优势害虫类群的虫口数量 ,提高各类群落的多样性和均匀度 ,增强天敌的自然控制能力 ,使第 2茬苜蓿的害虫数量一直保持在较低的水平。在苜蓿种子生产田 ,当 6月上旬害虫进入始盛期后 ,数量开始急速增长 。

Cutting is an important measure in maintaining alfalfa pasture. Choice of times and intervals for cutting directly affect the insect community composition and dynamics. The seasonal dynamics of insect communities on alfalfa pasture were investigated with biodiversity measures including species richness (S), unit numbers (N), Shannon's Index (H′), and evenness (E). The results showed that, in terms of species richness of the community, cutting influenced some rare species of insect pests rather than dominating and common species. Species richness of insect reduced with increase in cutting times. On the other hand, cutting had little effect on the species and populations of natural enemies due to their shifting from alfalfa plants to other crops nearby or dropping on the ground during cutting. In fact, the study showed that the populations of natural enemies can reach comparatively high density level from an initial low level after cutting because of their faster population growth than insect pests. Both the diversity and evenness of insect communities varied significantly and with regularity over time and were affected a lot by the number of cutting times. The populations of some dominant pests such as aphids, thrips, and alfalfa plant bugs began to boom when alfalfa plants changed from budding blossoming in the first ten-day period of June. It is suggested to cut at this time because both the diversity and evenness of the over an insect community and insect pests sub-communities are at low levels. Cutting in this period can effectively reduce the populations of dominant insect pests, and at the same time, increase insect community diversity and evenness to strengthen the insect pest control by natural enemies, and therefore restrain the populations of insect pests at low levels during the second crop. For alfalfa seed production fields, low temperature slowed the growth of pest populations before mid-May. After that, rising temperature sped up the growth of pest numbers, which attained higher levels than the slower increasing natural enemies. As mentioned above, the best moment to control insect pests populations could be the period in the first ten days of June, because measures employed to control pests in this period were not only effective to reduce pest populations, but also helpful to protect natural enemies and improve the quality of alfalfa seed.