SENSITIVITY OF MAYFLY NYMPHS TO RED-LIGHT - IMPLICATIONS FOR BEHAVIORAL ECOLOGY

1. Visual sensitivity of the mayflies Stenacron interpunctatum (Say) and Stenonema vicarium (Walker) to red (650 run) and infra-red (950 nm) light was tested using a behavioural assay. Nymphs were placed in a runway and sequentially exposed to green light, red fight, infra-red light and no light (control) at one end of the runway. The distance run away from the light, and the number of alarm reactions to the light were recorded. 2. Both species reacted strongly to both red and green light, running significantly greater distances and reacting more frequently to these wavelengths of light than to either infrared light or the control. 3. These results show that unobtrusive observations of mayfly nocturnal behaviour should be made using infra-red, and not red light, for illumination. Previous studies of aquatic insect nocturnal behaviour may have produced biased results if red light was used.