Chemiluminescent tags for tracking insect movement in darkness: Application to moth photo-orientation

The flight tracks of Manduca sexta (Lepidoptera: Sphingidae) flying toward a 5 watt incandescent light bulb were recorded under low light conditions with the aid of a camera-mounted photomultiplier and a glowing marker technique. Small felt pads bearing a chemiluminescent (glowing) material, Cyalume®, were affixed to the abdomens of free-flying moths. Tagged insects orienting to a dim incandescent bulb were easily visible to the naked eye and were clearly captured on videotape. On their initial approach to the light source, M. sexta were found to orient at a mean angle of-0.22°± 2.7°(mean ± SEM). The speed of the initial approach flight (0.4 ± 0.03 m/s) was significantly faster than the speed immediately after passing the light (0.29 ± 0.02 m/s; t = 6.4, P<0.0001, n = 61). Flight tracks obtained from transcribed video records show M. sexta initially fly approximately at a light source and only after passing it, do they engage in circular flight around the source. M. sexta flight to lights does not entirely match any paths predicted by several light orientation mechanisms, including the commonly invoked light compass theory.