Vogel Cassandra, Chunga Timothy L, Sun Xiaoxuan, Poveda Katja, Steffan-Dewenter Ingolf
Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany.
Soils, Food and Healthy Communities, Ekwendeni, Mzimba District, Malawi.
PeerJ. 2021 Feb 19;9:e10732. doi: 10.7717/peerj.10732. eCollection 2021.
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: (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: ), (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.
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.
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.
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.
已知景观构成会影响农田中的益虫和害虫群落。因此，景观构成会影响昆虫为作物提供的生态系统（负）服务。尽管在温带地区的大规模农业中已经研究了景观对生态系统服务提供者的影响，但在这一研究领域中，热带小农户农业的代表性不足，尤其是在撒哈拉以南非洲地区。豆类作物可为脆弱的农民提供重要的粮食安全保障和土壤改良效益。然而，豆类作物的生产依赖传粉昆虫，尤其是蜜蜂（膜翅目：蜜蜂总科），并且易受虫害影响。我们在马拉维选择了10个木豆（豆科： （L.））田，其半径1公里范围内半自然栖息地和农业区域的比例各不相同，以研究：（1）半自然栖息地和农业区域的比例如何影响蜜蜂的丰度和丰富度以及食花芫菁（鞘翅目： ）的丰度，（2）受损花朵的比例以及开放花朵和套袋花朵之间的坐果差异是否与半自然栖息地或农业区域的比例相关，以及（3）这些景观中开放花朵和套袋花朵之间木豆的坐果差异是受虫害损害的限制还是因蜜蜂访花而改善。
我们在每个田块进行3次、每次10分钟、长度为15米的样带调查，以评估芫菁的丰度以及蜜蜂的丰度和丰富度。捕获蜜蜂并鉴定到（形态）物种。我们评估了花期期间被甲虫损坏的花朵比例。我们在每个田块的15株植物上进行了传粉者和害虫排除实验，以评估坐果是否受传粉者限制或受害虫影响。
在我们的研究中，田块周围农业区域比例相对较高的地区蜜蜂丰度更高。这种影响主要是由蜜蜂数量的增加驱动的。蜜蜂丰富度和甲虫丰度不受景观特征影响，套袋花朵和开放花朵之间的花朵损伤或坐果差异也不受景观特征影响。我们没有观察到蜜蜂密度或丰富度对坐果差异有积极影响，也没有观察到食花对坐果差异有负面影响。
在我们的研究区域，木豆开花较晚——进入旱季时才开花。这可以解释为什么我们观察到在以农业为主的地区蜜蜂密度较高，而不是在半自然栖息地较多的地区，因为在一年中的这个时候，这些地区蜜蜂的资源稀缺。因此，晚花豆类作物可能是季节性热带地区蜜蜂在资源稀缺时期的重要食物来源。我们的研究与在温带地区进行的研究之间模式上的差异凸显了在温带地区以外的地区进行景观尺度研究的必要性。
