Assessment of four flowering plant mixtures - Studying their attractiveness to beneficial insects for pollination and biocontrol

Summary

The study investigated the use of flowering plant mixtures for the enhancement of insect richness and diversity in urban environments. The study assessed the attractiveness of three mixtures to insects in comparison with a known bee- friendly mixture and investigated the interactions between flowering time, plant diversity, pollinator attractiveness and abundance of biocontrol agents. This BSc thesis was part of a study commissioned by PSR (Pro Specie Rara), FiBL (Research Institute of Organic Agriculture) and the Swiss wholesaler Coop. The plant mixtures were expected to provide essential resources such as shelter, food, and overwintering sites for pollinators and natural enemies of pests. A behavior software program was used to monitor eight different groups of pollinators, examining their behavioral patterns and overall abundance. Biocontrol agents were monitored for abundance at different life stages. Botanical assessments were conducted in raised bed boxes to establish correlations between flowering plant mixtures and beneficial insect monitoring. I assessed: 1) assessment of plant growth stages to understand flowering times and durations, and 2) plant and bare soil cover along with flower abundance to provide insight into vegetation dynamics and relationships. Results of the study suggest a correlation between flower abundance and pollinator activity in the different plant mixtures. Temporal patterns varied and showed different distributions of visiting insects in mixtures 1, 2 and 3. Wild bees and honeybees were the most abundant group of pollinators recorded, especially in the reference mixture. Analysis of time spent per flower visit showed consistently longer durations for honeybees, wild bees and syrphids in all mixtures if compared with other monitored pollinator groups. Honeybees spent more time per flower on mixtures 1, 2, and 3 than on the reference mixture, while wild bees showed a preference for mixture 2 and mixture 3 compared with mixture 1, suggesting differences in reward quality (nectar and pollen) or reward timing. Although the number of biocontrol agents was small, the study showed that the reference mixture was most attractive to biocontrol agents, while similar numbers of biocontrol agents were recorded in mixture 1 and mixture 2. Lacewings were the most abundant insect recorded in all mixtures. Mixture 3 appeared to be less attractive to biocontrol agents than the other mixtures tested. I suggest that, more frequent monitoring (4 times per week) would be required to improve the quality of the assessment. Additionally, I suggest optimizing the mixtures by adjusting the seed density as some species, such as Camelina Sativa and Triticum dicoccon showed a high dominance in the mixtures. Moreover, I suggest adjusting the composition by increasing the number of plant species of the mixtures (m1, m2, m3) as they had lower plant coverage compared to the reference mixture. In conclusion, this study highlighted the potential of flowering plant mixtures to enhance ecosystem services and contribute to biodiversity conservation in urban environments. It provided valuable insights into the selection and design of insect-friendly flowering plant mixtures to support sustainable practices. I conclude with a call for further analysis to explore weekly variation and correlations of biocontrol agents with botanical data, aiming for a comprehensive understanding of the dynamics within the specific plant-insect interactions. The results are promising for promoting sustainable practices in urban ecosystems and labeling these mixtures as "insect-friendly", but further studies should be conducted to make a conclusive statement.