Injurious Male-male Aggression and Female Chemical Incitation in the Lek Mating System of a New Fairy Moth Species (Incurvariidae; Lepidoptera).


Male fairy moth on ninebark, by Kari C. Roesch.

A new species of fairy moth (Incurvariiade), is described from northwestern Montana, U.S.A., together with a preliminary characterization of its lek mating system. Male mating swarms of 1-8 individuals occupy display areas of 2000-4000 cm3. These classical leks are anchored, in some cases with strong year-to-year consistency, within sunspots illuminating a local highpoint in the forest shrub layer featuring an adjoining vegetation gap (e.g., a footpath). Most display areas are above Ninebark (Physocarpus malvaceus) or Mountain Spray (Holodiscus discolor). Higher shrubs directly across from the gap may also be characteristic. The male's long white antennae and black wings marked with white crescents make them conspicuous while flying and landed. Males exhibit dramatic combative behaviors while flying and landed, involving attempts to slash one another's wings and body with tibial spurs. Females can be found 3-8 m from the lek, across its adjoining vegetation gap, perched at excellent vantage points for observing male activity. Experimental data suggest that females may chemically incite male-male aggression while visually monitoring the lek from these galleries. Female mate selection may consist of monitoring and inciting from the gallery until enough competition has occurred to reliably handicap lower quality males, followed by entry of the swarm to mate with the first male to couple with them in erratic flight. Females are probably protected from potentially dangerous misidentification as males by their sexually dimorphic bright orange "hairdoo."

UPDATE: Population numbers for the last two field seasons have been insufficient at Flathead Lake Biological Station to collect additional data on the mating system. To our knowledge, the station is the only place this species has ever been observed. If you may know of other populations of this apparently rare microlepidopteran species please notify Dr. Paul J. Watson

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