A44 Chemical disruptions

Topic

The insect relies on its olfactory receptors for three critical functions: detecting sex pheromones from its own species, locating food, and recognizing host plants; and it is precisely these olfactory receptors that environmental chemical disruptors—such as pesticides, artificial fragrances, and industrial compounds—can block or mimic.

Under normal conditions, the fraction of the insect's olfactory receptors activated by a natural odorant depends on the odorant's concentration and its affinity for the receptor, as described by the Hill isotherm: the higher the concentration and affinity, the greater the fraction of activated receptors.

When a disruptor acts by blocking the receptor, it does so through competitive inhibition: it competes directly with the natural odorant for the same active site on the olfactory receptor. This competition raises the insect's detection threshold in proportion to both the concentration of the disruptor present and its inhibitory potency—the more concentrated and potent the disruptor, the more natural odorant the insect requires to continue detecting the signal. As receptors become partially blocked in this manner, the range of the insect's pheromone-based communication is drastically reduced.

In the most extreme case, the disruptor does not block the receptor but mimics it: it acts as a full agonist of the olfactory receptor, effectively mimicking the insect's own pheromone. When this occurs, the insect's olfactory system can become artificially saturated with this false signal; unlike the partial blocking seen in the previous mechanism, this saturation completely prevents any genuine chemical communication.

However, the insect is not entirely defenseless against these forms of disruption; it possesses detoxification enzymes, such as glutathione transferase, capable of deactivating odorants—including chemical disruptors—directly within the olfactory lymph bathing its receptors. This enzymatic deactivation constitutes an adaptive mechanism that allows the insect to regain part of the detection capacity lost due to both competitive blocking and saturation by mimicry.

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