Just to clarify terminology up front; pyrethrins are the active ingredients (with the insecticidal activity) found in pyrethrum (the concentrate from chrysanthemum daisies).
The Repellant Effect of Pyrethrins
We quite often say that our Ecomist Insect Killer with Natural Pyrethrins kills and “repels” insects.
Pyrethrins act on the nervous systems of insects; initially hyper-stimulating the nerves, then later blocking nerve synapses leading to death. The repellency effect of pyrethrins is related to each insect’s individual response to the stimulation of their nervous system.
Mozzies respond slightly differently when they come into contact with pyrethrins. When they annoy us, most of time they are looking for a blood meal so that they can lay eggs. When pyrethrins affect their nervous system, they are unable to detect the things they look for when hunting for a meal (water vapour, carbon dioxide, heat), so they vacate the area until their body parts that allow them to detect meals are functioning properly again. If they are able to, they then continue searching for a meal elsewhere.
Because of their repellant effect, pyrethrins have a unique fit in the market place, and have become a very important commercial tool for insect control in homes and businesses.
The Phototropic Effect of Pyrethrins
Insects affected by pyrethrins, tend to fly in a crazed manner towards light; it’s called the phototropic effect.
If it is light outside, they will most often head for windows or doors, banging into them repeatedly as they keep trying to fly towards the light. If the window is slightly open, then they’ll be able to exit to the great outdoors where they’ll most likely die. If not, their crazed buzzing causes them to come into contact with even more pyrethrins which ultimately results in death.
The main benefit of the phototropic effect is that flies will most often move away from food and food preparation areas in search of light. With manually administered insecticides the likelihood of flies landing in food or in the food prep area is high.
Frequent, small doses of pyrethrins (as in that dispensed by Ecomist Dispensers), keep a certain amount of pyrethrins circulating in the air. This forces insects coming into area with an Ecomist Dispenser to move in the direction of a light source, which is normally behind them if they've come in from outside. That keeps them out in the first place, which is what want!