What the Nose Knows: The Science of Scent in Everyday Life by Avery Gilbert Page A

range of butterfly odors. Some are like confections (vanilla, chocolate, burnt sugar), others like flowers (freesia, jasmine, heliotrope, mango flower, honeysuckle, sweetbriar). Yet others are like herbs and spices (cinnamon, lemon verbena, orris root, sandalwood, musk). Longstaff also found a spectrum of unpleasant scents, some reminiscent of cockroach or muskrat, others of rancid butter, butyric acid, vinegar, acetylene, musty straw, cow dung, horse stable, horse urine, and ammonia.
    We now know that the lemony body odor of the Green-veined White contains alpha-pinene, beta-pinene, myrcene, limonene, linalool, p-cymene, neral, and citral. (The first five ingredients are also found in cannabis oil. Why should a psychoactive hemp plant and a butterfly share odors? Nature is wonderfully strange.) Males of the Green-veined White have another scent, which they hold in reserve for special occasions. It is methyl salicylate, easily recognized as the odor of wintergreen (or Pepto-Bismol). The male uses it as an antiaphrodisiac: he transfers the scent into the female at mating and it discourages other males from copulating with her afterward. Related species have their own versions of this turn-off tactic: the Small White uses a blend of methyl salicylate and indole; the Large White uses benzyl cyanide. These chemical countermeasures can backfire, as when the Large White’s antiaphrodisiac aroma draws unwelcome attention of a tiny parasitic wasp called
Trichogramma brassicae.
When a female wasp smells a recently mated Large White female, she grabs on and hitches a ride. As the butterfly lays her eggs, the wasp parasitizes them by laying her own eggs inside them, and her young later use the butterfly’s eggs for food. In the end, the male Large White who tried to defend his genetic investment ended up sacrificing some of his potential offspring.
     
    N ATURAL BOTANICAL scents have a soft-focus, flower-child ambience about them. They are perceived as innocuous and innocent, a gift from Earth Mother Gaia to aromatherapists everywhere. In reality, they are biological communication systems, a way for plants and animals to talk to each other. This also makes them instruments of deception and treachery. Once a smell is used as a signal, other organisms can turn it to their selfish advantage. (Ask a female Large White how she feels about the parasitic wasp on her back.) A Mediterranean plant called the dead-horse arum fakes the stench of rotting meat. It attracts blowflies looking to lay eggs on a nice ripe carcass. The blowfly gets fooled into pollinating the plant for free, traveling from one stinky plant to the next carrying pollen on its legs, in what has been called “a striking example of evolutionary cunning that exploits insects for pollination purposes.” Other examples are more sinister and almost perverse. An Australian orchid emits a smelly molecule called 2-ethyl-5-propylcyclohexan-1,3-dione, which happens to be the exact molecule produced as a sex attractant by females of the wasp species
Neozeleboria cryptoides.
When the orchid joins the action, the result is an aroma-based, cross-species sexual deception in which hapless male wasps attempt to copulate with the orchids. In the end, the orchid is pollinated and the male wasp is frustrated. Sex and exploitation are never far apart.
    In nature, smells also serve defensive purposes. Essential oils, cherished as healing elixirs by aromatherapists, are really weapons in the ongoing battle between a plant and its predators. Take the orange tree as an example. It provides three different materials used in perfumery: neroli oil from its flower, orange peel oil from its fruit, and pettigrain from its leaves. Orange trees didn’t evolve for the perfumer’s convenience. Flowers smell good to attract pollinators; fruits smell and taste good to attract seed dispersers. A leaf releases volatile aromatic compounds as soon as an herbivore bites into it. This makes the leaf unpalatable or