Background Landscape composition is known to affect both beneficial insect and pest communities on crop fields. Landscape composition therefore can impact ecosystem (dis)services provided by insects to crops. Though landscape effects on ecosystem service providers have been studied in large-scale agriculture in temperate regions, there is a lack of representation of tropical smallholder agriculture within this field of study, especially in sub-Sahara Africa. Legume crops can provide important food security and soil improvement benefits to vulnerable agriculturalists. However, legumes are dependent on pollinating insects, particularly bees (Hymenoptera: Apiformes) for production and are vulnerable to pests. We selected 10 pigeon pea (Fabaceae: Cajunus cajan (L.)) fields in Malawi with varying proportions of semi-natural habitat and agricultural area within a 1 km radius to study: (1) how the proportion of semi-natural habitat and agricultural area affects the abundance and richness of bees and abundance of florivorous blister beetles (Coleoptera: Melloidae), (2) if the proportion of flowers damaged and fruit set difference between open and bagged flowers are correlated with the proportion of semi-natural habitat or agricultural area and (3) if pigeon pea fruit set difference between open and bagged flowers in these landscapes was constrained by pest damage or improved by bee visitation. Methods We performed three, ten-minute, 15 m, transects per field to assess blister beetle abundance and bee abundance and richness. Bees were captured and identified to (morpho)species. We assessed the proportion of flowers damaged by beetles during the flowering period. We performed a pollinator and pest exclusion experiment on 15 plants per field to assess whether fruit set was pollinator limited or constrained by pests. Results In our study, bee abundance was higher in areas with proportionally more agricultural area surrounding the fields. This effect was mostly driven by an increase in honeybees. Bee richness and beetle abundances were not affected by landscape characteristics, nor was flower damage or fruit set difference between bagged and open flowers. We did not observe a positive effect of bee density or richness, nor a negative effect of florivory, on fruit set difference. Discussion In our study area, pigeon pea flowers relatively late—well into the dry season. This could explain why we observe higher densities of bees in areas dominated by agriculture rather than in areas with more semi-natural habitat where resources for bees during this time of the year are scarce. Therefore, late flowering legumes may be an important food resource for bees during a period of scarcity in the seasonal tropics. The differences in patterns between our study and those conducted in temperate regions highlight the need for landscape-scale studies in areas outside the temperate region.

中文翻译：

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在热带小农农场的晚花豆类作物上农业较多的景观中蜜蜂丰度较高，但害虫丰度不高

背景 已知景观构成会影响农田上的益虫和害虫群落。因此，景观构成会影响昆虫为作物提供的生态系统（不）服务。尽管已经在温带地区的大规模农业中研究了景观对生态系统服务提供者的影响，但该研究领域缺乏热带小农农业的代表性，特别是在撒哈拉以南非洲地区。豆类作物可以为脆弱的农民提供重要的粮食安全和土壤改良效益。然而，豆类依赖于授粉昆虫，特别是蜜蜂（膜翅目：蜜蜂形目）进行生产，并且容易受到害虫的侵害。我们选择了 10 个木豆（豆科：Cajunus cajan (L. )) 在马拉维 1 公里半径范围内具有不同比例的半自然栖息地和农业区的田地进行研究：(1) 半自然栖息地和农业区的比例如何影响蜜蜂的丰度和丰度以及食花水泡的丰度甲虫（鞘翅目：Melloidae），（2）如果开放和袋装花之间的花朵受损比例和坐果差异与半自然栖息地或农业区的比例相关，以及（3）如果木豆开放之间的坐果差异这些景观中的袋装花卉受到害虫损害的限制或蜜蜂访问的改善。方法 我们对每个田地进行 3 次、10 分钟、15 m 的横断面，以评估水疱甲虫的丰度以及蜜蜂的丰度和丰富度。蜜蜂被捕获并识别为（形态）物种。我们评估了开花期间被甲虫破坏的花朵比例。我们对每块田地的 15 株植物进行了传粉媒介和害虫排除实验，以评估坐果是否受传粉媒介限制或受害虫限制。结果 在我们的研究中，在农田周围的农业面积相对较多的地区，蜜蜂的丰度较高。这种影响主要是由蜜蜂的增加驱动的。蜜蜂丰富度和甲虫丰度不受景观特征的影响，袋装花和开放花之间的花损或坐果差异也不受影响。我们没有观察到蜜蜂密度或丰富度的积极影响，也没有观察到花卉对坐果差异的负面影响。讨论 在我们的研究区域，木豆开花时间相对较晚——直到旱季。这可以解释为什么我们在以农业为主的地区而不是在一年中这个时候蜜蜂资源稀缺的半自然栖息地较多的地区观察到更高密度的蜜蜂。因此，在季节性热带稀缺时期，晚开花豆类可能是蜜蜂的重要食物资源。我们的研究与在温带地区进行的研究之间的模式差异突出了在温带地区以外地区进行景观尺度研究的必要性。