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Suffolk Natural History, Vol. 55
DIPTERA REPORT 2019 PETER VINCENT I am starting this Diptera report with some disturbing observations on the catastrophic fall in global insect populations as well as on some more specific research concerning the decline of pollinating insects in Britain. A report was published earlier this year which gained headlines across the media. It was a comprehensive review of 73 historical research papers on insect declines from across the globe; the conclusion of which was that 40% of insects may become extinct over the next few decades. The main drivers of species declines appear to be in order of importance: i) habitat loss and conversion to intensive agriculture and urbanisation; ii) pollution, mainly that by synthetic pesticides and fertilisers; iii) biological factors, including pathogens and introduced species; and iv) climate change (Sånchez-Bayo & Wyckhuys, 2019). Despite this paper being one of the most comprehensive analyses of the state of the world's insect populations it still contains substantial gaps. This is because not all insect groups have been studied equally; one order that is frequently overlooked is Diptera. Diptera have often been ignored, primarily because they are difficult to study. It is often hard to identify the species both from the larval and adult stages, especially compared to other groups such as moths and butterflies. The enormous biomass of flies supports a whole range of other animal groups, particularly the more traditionally charismatic birds and bats. This makes the fact that so little is officially known about the number and population trends of flies all the more concerning. The Diptera, which include everything from houseflies and hoverflies to midges and mosquitoes, are hugely important due to their sheer numbers, but they are also significant contributors to most ecological functions such as pollination. Some work is now being done, especially into the decline of economically pollinating flies. A recent paper that comments on declines in pollinating insects in Britain, uses occupancy models for 353 wild bee and hoverfly species between 1980 and 2013 (Powney et al., 2019). They found that in both hoverflies and bees a third of species assessed declined in range, while just a tenth increased their geographic distribution. Furthermore, they estimated a staggering net loss of over 2.7 million occupied 1 km2 grid cells across all species. Rates of distribution declines were similar for bees and hoverflies (25% and 24% respectively), although declines in pollinator evenness suggest that losses were concentrated in rare species. Finally, on pollinating hoverflies, some fascinating research into mass migration by hoverflies using insect monitoring radars revealed that up to 4 billion hoverflies (80 tonnes of biomass) travel high above southern and eastern Britain each year on seasonal migrations. These hoverflies transport billions of grains of pollen between Europe and Britain and locally produced populations consume some 6 trillion aphids and make billions of flower visits (Wooton, et al. 2019). Undoubtedly, a highlight was the discovery of the Conopid fly Leopoldius calceatus (Rondani, 1857) by David Basham at Purdis Heath near Ipswich. Although, the fly was found in 2018, details have only recently been published (Clements & Basham, 2019). This record of L. calceatus is considered new to the British Isles. Of the six species of
Trans. Suffolk Nat. Soc. 55 (2019)