Preliminary New Study Indicates Possible Dramatic Decline in the Diversity of Insects Visiting Flowers of Jarrah (<i>Eucalyptus Marginata</i>) in Kings Park Over 26 Years

The recent decline of terrestrial insects in many parts of the world is of growing concern due to the fundamental ecosystem services they perform. Pollination is a vital ecosystem service predominantly performed by insects, with inestimable environmental and economic benefits. Accurate assessment and management of insect pollinator declines, and of other ecosystem impacts are hindered by a lack of long-term monitoring data and notably an absence of Southern Hemisphere studies. This preliminary study aims to address some of these gaps by determining if the diversity of insect floral visitors and potential pollinators of the canopy tree species Jarrah (Eucalyptus marginata) within Kings Park may have changed over 26 years by replicating the methods employed by previous research (undertaken by Yates et al. in 2005). Additionally, this study aims to determine if the relative abundance of the introduced European honeybee (Apis mellifera) compared to native bees visiting Jarrah flowers may have also changed. We observed insect visitors to flowers at three trees across the morning, midday, and evening over three consecutive days in mid-December 2023 (peak flowering). A total of 3023 individual observations were made, recording insects of 7 orders, 25 families, 39 genera, and 45 species. We found that abundances were comparable to 26 years ago but found a substantial shift in the composition of insect visitors with 46% less species documented and only 25% of species reoccurring. Ten additional families were observed that were not documented 26 years ago, with most visitors capable of performing pollination to varying efficacies. Ants had replaced the European honeybee as the most common visitor to Jarrah flowers, and while the relative abundance of honeybees was still significantly greater than native bees, the proportion of honeybee visitors had declined, at least at the time of our study. The documented shift in the composition of Jarrah insect pollinators should be confirmed by more replicated studies in Kings Park, and highlights the importance of long-term monitoring, and the need for further avenues of urban pollination research to accurately assess and address any widespread decline of insects. This is important for protecting the pollination services that insect pollinators provide at local and global scales.