Ostrom P H, Colunga-Garcia Manuel, Gage Stuart H
206 Natural Science Building, Department of Geological Sciences, Michigan State University, East Lansing, MI 48824-1115, USA fax: 517-353-8787, , , , , , US.
Department of Entomology, Michigan State University, East Lansing, MI 48824-1115, USA, , , , , , US.
Oecologia. 1996 Dec;109(1):108-113. doi: 10.1007/s004420050064.
Quantifying pathways of energy transfer between plants, pests, and beneficial insects is a necessary step toward maintaining pest stable agroecosystems in the absence of chemical subsidies. A diet switching experiment utilizing a predatory ladybird beetle, Hippodamia variegata (Goeze), evaluated the use of naturally occurring stable C and N isotopes as an economically feasible and safe method for quantifying pathways of energy flow within agroecosystems. Stable isotope values of the ladybird beetle Coleomegilla maculata lengi (Timberlake) collected from an agroecosystem were used to estimate the relative amount of C and N derived from agricultural plants and incorporated by ladybird beetles based on mass balance equations. At the beginning of the diet-switching experiment δC and δN values of H. variegata (-12.0‰ and 6.3‰, respectively) differed by -0.2‰ and 2.9‰ from the aphids that were provided exclusively as their diet. These data are consistent with previous estimates of trophic level isotope effects. After switching the diet of H. variegata to an alternative food, isotope values of H. variegata gradually shifted toward expected values for individuals fed this diet (-22.9‰ and 8.8‰ for δC and δN values, respectively). Isotope values of another ladybird beetle, C. maculata, collected from the field indicated that in May, alfalfa and maize (pollen) obtained in the previous year contributed 32% and 68% of the C or N to the diets of these individuals and in August, 52%, 6%, and 42% of the C or N assimilated by these insects was derived from alfalfa, wheat, and maize, respectively. These data are consistent with expectations based on the relative abundance of C. maculata in various crops during the season. The field and laboratory data are a clear indication that isotope values are sensitive to dietary changes on a relatively short time scale (days) and provide a strong basis for the use stable C and N isotope to trace energy flow patterns of these beneficial organisms within agroecosystems.
量化植物、害虫和益虫之间的能量传递途径是在没有化学补贴的情况下维持有害生物稳定的农业生态系统的必要步骤。一项利用捕食性瓢虫——多异瓢虫（Hippodamia variegata (Goeze)）进行的饮食转换实验，评估了使用天然存在的稳定碳和氮同位素作为一种经济可行且安全的方法来量化农业生态系统内的能量流动途径。从农业生态系统中收集的瓢虫黄斑盘瓢虫（Coleomegilla maculata lengi (Timberlake)）的稳定同位素值，被用于根据质量平衡方程估算来自农业植物并被瓢虫吸收的碳和氮的相对量。在饮食转换实验开始时，多异瓢虫的δC和δN值（分别为-12.0‰和6.3‰）与仅作为其食物提供的蚜虫相比，δC值相差-0.2‰，δN值相差2.9‰。这些数据与先前对营养级同位素效应的估计一致。在将多异瓢虫的食物转换为另一种食物后，多异瓢虫的同位素值逐渐向食用这种食物的个体的预期值转变（δC和δN值分别为-22.9‰和8.8‰）。从田间收集的另一种瓢虫——黄斑盘瓢虫的同位素值表明，在5月，上一年获得的苜蓿和玉米（花粉）分别为这些个体的饮食贡献了32%和68%的碳或氮，而在8月，这些昆虫同化的碳或氮中，分别有52%、6%和42%来自苜蓿、小麦和玉米。这些数据与基于该季节不同作物中黄斑盘瓢虫相对丰度的预期一致。田间和实验室数据清楚地表明，同位素值在相对较短的时间尺度（数天）内对饮食变化敏感，并为使用稳定碳和氮同位素追踪这些有益生物在农业生态系统内的能量流动模式提供了有力依据。
