Context African production landscapes are diverse, with multiple cassava cultivars grown in small patches amongst a diversity of other crops. Studies on how diverse smallholder landscapes impact herbivore pest outbreak risk have not been carried out in sub-Saharan Africa. Objectives Bemisia tabaci is a cryptic pest species complex that cause damage to cassava through feeding and vectoring plant-virus diseases and are known to reach very high densities in certain contexts. However, the factors driving this phenomenon are unclear. Methods Bemisia density data in cassava across a large number of sites representing a geographic gradient across Uganda, Tanzania and Malawi were collected. We tested whether in-field or landscape factors associated with land-use patterns underpinned Bemisia density variability and parasitism. Results We found the B. tabaci SSA1 species dominated our study sites, although other species were also common in some cassava fields. Factors associated with the surrounding landscape were unimportant for explaining variability in adult density, but the in-field variables of cassava age and cultivar were very important. The density of nymphs and the parasitism of nymphs was heavily influenced by a diversity of landscape factors surrounding the field, including the size of focal cassava field, and area of cassava in the landscape. However, unlike the trend from many other studies on drivers of natural enemy populations, this pattern was not solely related to the amount of non-crop vegetation, or the diversity of crops grown in the landscape. Conclusions Our findings provide management options to reduce whitefly abundance, including describing the characteristics of landscapes with high parasitism. The choice of cassava cultivar by the farmer is critical to reduce whitefly outbreak risk at the landscape-scale.

中文翻译：

---

景观因素及其如何影响东非木薯田的粉虱害虫

背景 非洲的生产环境多种多样，多种木薯品种在其他作物的多样性中小块种植。尚未在撒哈拉以南非洲开展关于多样化小农景观如何影响食草动物害虫爆发风险的研究。目的 烟粉虱是一种隐蔽的害虫物种复合体，通过摄食和传播植物病毒病害对木薯造成损害，并且已知在某些情况下会达到非常高的密度。然而，导致这种现象的因素尚不清楚。方法 收集了代表乌干达、坦桑尼亚和马拉维地理梯度的大量地点的木薯 Bemisia 密度数据。我们测试了与土地利用模式相关的田间或景观因素是否支持 Bemisia 密度变异和寄生。结果我们找到了 B. 烟粉虱 SSA1 物种在我们的研究地点占主导地位，尽管其他物种在一些木薯田中也很常见。与周围景观相关的因素对于解释成虫密度的变异性并不重要，但木薯年龄和品种的田间变量非常重要。若虫的密度和若虫的寄生在很大程度上受到田地周围各种景观因素的影响，包括焦点木薯田的大小和景观中的木薯面积。然而，与许多其他关于天敌​​种群驱动因素的研究的趋势不同，这种模式不仅仅与非作物植被的数量或景观中种植的作物多样性有关。结论 我们的研究结果提供了减少粉虱丰度的管理选择，包括描述高寄生景观的特征。农民选择木薯品种对于减少景观尺度上的粉虱爆发风险至关重要。