Hypothesis
If pheromone detection in the hawkmoth runs through an ionotropic OR-Orco channel, then opening the Orco pore with an agonist should add to the pheromone-evoked response in olfactory receptor neurons.
What failed
In tip recordings from intact pheromone-sensitive sensilla, perfusing the Orco agonist VUAA1 did not boost pheromone responses within the first 1000 ms, although it raised the neurons' spontaneous firing in a dose- and time-of-day-dependent way.
Broken assumption
Insect odorant receptor-Orco complexes transduce pheromone signals as fast ionotropic channels in all species.
Why
The authors propose that in M. sexta Orco acts as a slower, second-messenger-dependent pacemaker channel that sets calcium baseline, rather than as the fast pheromone-gated pore.
From the published paper: Nolte et al. PLoS ONE, 2013. ↗CC BY