Pyrophilic smoke flies (Diptera: Platypezidae: Microsaniinae) from prescribed burnings in boreal Finland: occurrence and behaviour of adult flies and first observations of immature stages

Smoke flies (Diptera: Platypezidae: Microsania) are among the most specialized pyrophilic insects, exhibiting a strong and rapid reaction to smoke. Although their attraction to smoke has been known for a century worldwide, their immature stages and breeding habitat remained undiscovered. We hand-netted smoke flies at seven prescribed forest burns in boreal Finland between 2022 and 2024 and took soil samples in 2026. Smoke fly swarming and reproductive behaviour was observed at all burn sites. We obtained smoke flies of five out of the six Finnish species, with Microsania pallipes dominating (94%). Following the behavioural observations at burn sites, we later screened soil samples and found larvae identified as Microsania mtDNA COI barcodes in the burnt soil. We provide a first description of the larva of Microsania straeleni (Microsaniinae). Our discovery of the larval habitat in burnt soil resolved the long-standing knowledge gap on smoke fly breeding sites. The morphological characteristics of the immature stages will help elucidate the phylogenetic placement of the Microsaniinae within the Platypezoidea lineage.