A supposedly bioluminescent species of cockroach that would not glow: A case of scientific fraud, erroneous observation or bacterial infection?

Two reports of the discovery of bioluminescent cockroach species from South America in 1999 and 2003 led to a flurry of speculation on the evolution of the species, the likely function of the light supposedly emitted by the males of the species, and in fact whether these cockroaches were bioluminescent at all. No spectral emission data or biochemical analyses of luciferins or luciferases were available and observations as well as video recordings of the cockroaches failed to record any evidence of an emission of light. Considering the case against the so-called glowspots being able to emit light, it was concluded that the conspicuous spots on the pronotum of the males could play a part in mate choice or serve as a warning signal. Our re-examination of the issue confirms that the spots do not emit light and that, barring the possibility of scientific fraud or confusing fluorescence with bioluminescence, individual cockroaches in the field might have been seen to glow due to an infection with a species of the cosmopolitan bacterial genus Photorhabdus. We were able to show that Photorhabdus luminescens bacteria can colonize specimens of the cockroach Blaptica dubia and there is no reason to doubt that other species of cockroaches could not also become infected by this luminescent insect pathogen.