Abstract Mustard fields (Brassica campestris: Brassicaceae) are mass flowering crops attracting a wide diversity of flower-visiting insects. Many studies have shown that the diversity of insects is higher near forest fragments than farther away from the forest edge and that Apis-bees numerically dominate such ecosystems. In this study, we investigated how insect diversity changes with distance from the forest edge (100 m, 1100 m, 2100 m) in mustard crop fields in Nepal. The effects of distance on both the abundance and richness of insects were evaluated using generalized linear mixed models, while Hill numbers were used to describe species diversity. We performed ordination analysis and PERMANOVA to examine the dissimilarity between insect communities at different distances. Finally, percent similarity was used to describe which insect species contributed most to the dissimilarity among distances. Our findings suggest that richness and abundance of the flower-visiting insects differed between distances of 100 m and 2.1 km from forest fragments. We found that values of all diversity measures were higher nearer to the forest fragments and moderately distant from the fragments. Accordingly, the ordination analysis corroborated the GLMMs, showing that insect community composition near to and moderately far from the forest fragments differed from that farther in the field. Additionally, we detected that solitary bee species (Andrena spp., Halictus spp. and Megachile lanata) outnumbered Apis-bees, greatly contributing to community discrimination among distances. Overall, we demonstrated that insect diversity within mustard crops is not homogeneous in Nepal. Cultivated plants farther from forest fragments are facing a deficit of diversity of flower-visiting insects. Furthermore, the role and the nesting habitat of solitary bees sampled here should be investigated, as they may contribute to mustard pollination in Nepal.

中文翻译：

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远离森林碎片的芥菜植物的访花昆虫多样性较低

摘要 芥菜田（Brassica campestris：Brassicaceae）是大量开花作物，吸引了种类繁多的访花昆虫。许多研究表明，靠近森林碎片的昆虫的多样性高于远离森林边缘的昆虫，而且蜜蜂在数量上在这些生态系统中占主导地位。在这项研究中，我们调查了尼泊尔芥菜田中昆虫多样性如何随着距森林边缘（100 m、1100 m、2100 m）的距离而变化。使用广义线性混合模型评估距离对昆虫丰度和丰富度的影响，而希尔数用于描述物种多样性。我们进行了排序分析和 PERMANOVA 以检查不同距离的昆虫群落之间的差异。最后，百分比相似性用于描述哪些昆虫物种对距离之间的差异贡献最大。我们的研究结果表明，在距森林碎片 100 m 和 2.1 km 的距离内，访花昆虫的丰富度和丰度不同。我们发现所有多样性措施的值在靠近森林碎片和适度远离碎片的地方更高。因此，排序分析证实了 GLMM，表明靠近和适度远离森林碎片的昆虫群落组成与远离野外的昆虫群落组成不同。此外，我们检测到孤独的蜜蜂物种（安德雷纳属、Halictus 属和 Megachile lanata）的数量超过了蜜蜂，极大地促进了距离之间的社区歧视。全面的，我们证明了芥菜作物中的昆虫多样性在尼泊尔并不是同质的。远离森林碎片的栽培植物正面临着访花昆虫多样性的不足。此外，应该调查这里采样的独居蜜蜂的作用和筑巢栖息地，因为它们可能有助于尼泊尔的芥菜授粉。