Cereal Aphid Colony Turnover and Persistence in Winter Wheat

An understanding of spatial and temporal processes in agricultural ecosystems provides a basis for rational decision-making with regards to the management and husbandry of crops, supporting the implementation of integrated farming strategies. In this study we investigated the spatial and temporal distribution of aphid pests (Sitobion avenae and Metopolophium dirhodum) within winter wheat fields. Using an intensive sampling programme we investigated distributions at both the small (single shoot) and large (field) scales. Within two fields, a grid with 82 locations was established (area 120 m by 168 m). At each location, 25 shoots were individually marked and aphid counts by observation conducted on 21 and 22 occasions as the crop matured, resulting in 43,050 and 45,100 counts being conducted in the two fields respectively. We quantified field scale spatial distributions, demonstrating that spatial pattern generally emerged, with temporal stability being both species- and field- dependent. We then measured turnover of colonies at the small (individual shoot) and large (field) scales by comparing consecutive pairs of sampling occasions. Four turnover categories were defined: Empty (no aphids recorded on either occasion); Colonised (aphids recorded on the second occasion but not the first); Extinction (aphids recorded on the first occasion but not the second); Stable (aphids recorded on both occasions). At the field scale, population stability soon established, but, at the small scale there was a consistently high proportion of unoccupied shoots with considerable colonisation and extinction and low stability. The redistribution of aphids within the crop at the local scale is a vulnerability which could be used to disrupt population development – by mediating exposure to ground-active natural enemies and by incurring a metabolic cost caused by the physiological demands to re-establish on a nearby host plant.

对农业生态系统中的空间和时间过程的理解，为作物管理与饲养的合理决策提供了基础，并支持了综合农业战略的实施。在本研究中，我们调查了蚜虫害虫（Sitobion avenae 和 Metopolophium dirhodum）在冬小麦田中的空间和时间分布。通过密集的采样计划，我们在小尺度（单个植株）和大规模（田地）上研究了分布情况。在两个田地内，建立了一个包含82个位置的网格（面积120米乘以168米）。在每个位置，标记了25个植株，并在作物成熟期间观察到的21和22次 occasions 进行了蚜虫计数，分别在这两个田地中进行了43,050和45,100次计数。我们量化了田地尺度的空间分布，证明了空间模式通常出现，且时间稳定性受物种和田地依赖。随后，我们通过比较连续的采样 occasions 来测量小尺度（单个植株）和大规模（田地）的种群周转。定义了四个周转类别：空缺（两次 occasions 均未记录到蚜虫）；占据（第二次 occasions 记录到蚜虫但第一次没有）；灭绝（第一次 occasions 记录到蚜虫但第二次没有）；稳定（两次 occasions 均记录到蚜虫）。在田地尺度上，种群稳定性迅速建立，但在小尺度上，有持续的高比例空置植株，且伴随着显著的占据和灭绝，稳定性较低。在局部尺度上，蚜虫在作物内部的重新分配是一种脆弱性，这可以被用来扰乱种群发展——通过调节对地面活跃天敌的暴露，以及通过由于在附近宿主植物上重新建立生理需求而引起的代谢成本。