Higher richness and abundance of flower-visiting insects close to natural vegetation provide contrasting effects on mustard yields

The conservation of pollinating insects in agriculture is a global concern since the diversity of such organisms may affect the productivity of pollination-dependent crops. In this study, we assessed (i) how distances from natural vegetation affect the diversity (guilds, richness, abundance) of flower-visiting insects within mustard crops in Nepal, (ii) how insect richness and abundance are related to mustard yields (weight of seeds) and (iii) the contribution of flower-visiting insects to mustard pollination by conducting pollinator exclusion experiments. To analyse these data, we carried out (i) hierarchical clustering followed by a Procrustes analysis as well as a generalized linear mixed model and (ii), (iii) linear mixed models. We found that the guild composition was not similar near and far from natural vegetation, indicating a tendency for Apis bees to displace in opposite directions relative to non-Apis bees. Nevertheless, while both richness and abundance were higher nearer natural vegetation, the former showed a stronger and more positive effect on mustard yields than the latter. Furthermore, we found that mustard flowers have a significant requirement for insect pollination since productivity increased by similar to 70% with insect visitation. Overall, our data suggest that the diversity of flower-visiting insects enlarges nearer to natural vegetation. However, the results indicate that species richness may be more relevant than abundance to mustard production. As such, we suggest that the maintenance of natural vegetation could be considered a strategy for ensuring the presence of multiple pollinator species within mustard fields to promote its long-term sustainability in Nepal.

Automated summary

The study indicates that the diversity of flower-visiting insects is higher near natural vegetation, with richness and abundance showing a greater impact on mustard yields. Species richness appears to be more critical for mustard production than insect abundance. The maintenance of natural vegetation is recommended to ensure the presence of multiple pollinator species within mustard fields for long-term sustainability in Nepal.