Consuming putrid food can be lethal as it allows bacterial
pathogens to enter the digestive system. To detect signs of
decay and thus allowing us and other animals to avoid such food
poisoning is one of the main tasks of the sense of smell.
Behavioral scientists and neurobiologists at the Max Planck
Institute for Chemical Ecology in Jena, Germany, have now for
the first time decoded the neural mechanisms underlying an
escape reflex in fruit flies (Drosophila) activated in order to
avoid eating and laying eggs in food infected by toxic
microorganisms. A super-sensitive and completely dedicated
neural line, from olfactory receptor, via sensory neuron and
primary brain neurons, is activated as soon as the tiniest
amount of geosmin is in the air. Geosmin is a substance released
by bacteria and mold fungi toxic to the fly. This stimulus
overrides all other food odor signals, irrespective of how
attractive they are on their own. Consequently, geosmin is a
full STOP signal that prevents flies from eating and laying