Low extinction risk in the flower fly fauna of northeastern North America

Introduction Flower flies (Diptera: Syrphidae; also known as hoverflies) are important pollinators of wild and cultivated plants. Other pollinators such as bees have declined, and many flower flies in Europe and Chile have been documented to be threatened with extinction. The status of other flower fly faunas is currently unknown. Aims/Methods We assessed the rangewide conservation status of flower flies that occur in Northeastern North America where there is a diverse fauna of 323 native species. Over 150,000 records, drawn from a locality database compiled for a recently published field guide, additional museum records, recent field surveys, and citizen science records, informed the assessments. Results We found that a minimum of 11 species are at risk of rangewide extinction, 267 have lower extinction risk, and 45 had insufficient data to assess. Our best estimate is that 4.0% of species are at risk, assuming data-insufficient species are at risk at the same rate as data sufficient species. The range for this estimate is 3.4–17.3% at risk, assuming that none or all data-insufficient species are at risk, respectively. Discussion Factors causing extinction risk in the fauna we studied are poorly known, although habitat destruction likely explains the decline in one species. While at-risk species mostly have saprophagus or brood parasitic larvae, trophic relationships are confounded by phylogeny (the subfamilies Eristalinae and Microdontinae account for most saprophagus or brood parasitic species). The broad geographical ranges of most species likely contributed to the low rate of imperilment. Implications for insect conservation The small percentage of at-risk flower flies in northeastern North America bodes well for the health of ecosystems there. The results contrast with the situation in Europe, underscoring geographic heterogeneity in flower fly conservation status.