Scale insect host ranges are broader in the tropics

The specificity of the interactions between plants and their consumers varies considerably. The evolutionary and ecological factors underlying this variation are unclear. Several potential explanatory factors vary with latitude, for example plant species richness and the intensity of herbivory. Here, we use comparative phylogenetic methods to test the effect of latitude on host range in scale insects. We find that, on average, scale insects that occur in lower latitudes are more polyphagous. This result is at odds with the general pattern of greater host-plant specificity of insects in the tropics. We propose that this disparity reflects a high cost for host specificity in scale insects, stemming from unusual aspects of scale insect life history, for example, passive wind-driven dispersal. More broadly, the strong evidence for pervasive effects of geography on host range across insect groups stands in stark contrast to the weak evidence for constraints on host range due to genetic trade...植物与其取食者之间的相互作用特异性差异显著。支撑这一差异的进化与生态因子仍未明确。诸多潜在解释因子随纬度梯度发生变化，例如植物物种丰富度与植食作用强度。本研究采用比较系统发育学方法（comparative phylogenetic methods），检验纬度对介壳虫（scale insects）宿主范围的影响。研究发现，平均而言，分布于低纬度地区的介壳虫多食性更强。这一结果与‘热带地区昆虫宿主植物特异性更强’的普遍认知相悖。我们认为，这种差异源于介壳虫宿主特异性所需承担的高昂演化成本，这一成本源自介壳虫生活史的独特特征，例如依靠风力进行的被动扩散。更广泛而言，诸多研究已证实地理因素对各类昆虫的宿主范围具有广泛影响，这与遗传权衡（genetic trade）相关的宿主范围限制证据匮乏形成鲜明对比……