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Two main hypotheses on how the TOs work:
1. they produce a volatile (airborne) substance
2. they produce a non-volatile or low-volatile stimulus
   a. tactile stimulus
   b. low-volatility substrate-bound secretion

It had long be assumed that the TOs emitted a volatile, airborne substance that attracted and alerted ants and made them more aggressive. Previous experimental evidence supports the volatile hypothesis, and Pierce 2002 states flatly that the TOs work by producing a volatile substance.

However, the work of Weeks shows that this is not always the case. Her results convincingly demonstrate that, for H. isola, the TOs must touch the ant to communicate with it. If the TOs of H. isola were producing a volatile substance, the ants would not need to touch the TO to react.

Most the lycaenids that have been studied are specialists, interacting with only one or a few species of ants. In these cases, it is plausible that the lycaenid could emit a volatile that mimics the alarm pheromone of their attendant ants.

But ant alarm pheromones vary greatly among species and they involve mixtures of compounds with species-specific components. Therefore, if you're aiming at more than one ant species, you can't use an alarm pheromone.

For H. isola, a generalist, a tactile cue is much more appropriate.

Weeks' experiments did not address the question of whether the H. isola TOs employ a tactile stimulus, a low-volatility substrate-bound secretion, or a combination.

Next: Weeks' other important findings.