Effect of bulb type on moth trap catch and composition in UK gardens

Light traps are a key method for monitoring moth populations. A wide variety of light sources are employed for this purpose, differing in brightness and spectrum. Relatively little is known about how this affects the resulting sample. We analyse seven moth trap bulb types using 10 years of records from the Garden Moth Scheme (GMS) to provide the largest and most comprehensive comparison of moth trap bulb types to date. The total abundance of moths caught by a trap is strongly linked to bulb wattage and brightness. We estimate that Heath traps catch fewer moths than Robinson or Skinner-stye traps. Ordination models indicated that Mercury Vapour bulbs collected a distinct fauna to Actinic bulbs. Species composition also varied between Actinic bulbs which differ in brightness, with brighter Actinic traps tending to collect a larger proportion of large-winged species. We develop hypotheses whereby large-winged, strong-flying moths are more strongly affected by artificial light (arising from moth traps or other sources). We explore how this hypothesised mechanism may result in negative fitness effects for larger, mobile moth species. Our findings have significant consequences for survey design, citizen science projects and understanding the impact of ALAN on the moth community.