CHEMILUMINESCENT TAGS FOR TRACKING INSECT MOVEMENT IN DARKNESS - APPLICATION TO MOTH PHOTOORIENTATION

The flight tracks of Manduca sexta (Lepidoptera: Sphingidae) flying to ward a 5 watt incandescent light bulb were recorded under low light co nditions with the aid of a camera-mounted photomultiplier and a glowin g marker technique. Small felt pads bearing a chemiluminescent (glowin g) material, Cyalume((R)), were affixed to the abdomens of free-flying moths. Tagged insects orienting to a dim incandescent bulb were easil y visible to the naked eye and were clearly captured on videotape. On their initial approach to the light source, M. sexta were found to ori ent at a mean angle of -0.22 +/- 2.7 degrees (mean +/- SEM). The speed of the initial approach flight (0.4 +/- 0.03 m/s) was significantly f aster than the speed immediately after passing the light (0.29 +/- 0.0 2 m/s; t = 6.4, P < 0.0001, n = 61). Flight tracks obtained from trans cribed video records show M. sexta initially fly approximately at a li ght source and only after passing it, do they engage in circular fligh t around the source. M. sexta night to lights does not entirely match any paths predicted by several light orientation mechanisms, including the commonly invoked light compass theory.