Question:
Can I use dish soap instead of insecticidal soap to treat for insect pests?Answer:
While they are both called "soaps," dish soap (like Dawn or Palmolive) is not a replacement for insecticidal soap.
Dish soap is actually more accurately classified as a detergent, not a soap. Soap is a molecule composed of salts (such as potassium or sodium) and fatty acids. Detergents are derived from petrochemicals and are a different type of molecule.
While dish soaps (detergents) can cause issues for insects, their effect on pests is limited and highly variable. Dish soap is also much more likely to cause damage to the plant, such as phytotoxicity. Insecticidal soap is a true soap (usually potassium salts of fatty acids) created specifically to target pests. They work on contact by damaging the insect's cell membranes. The cell contents are able to leak from the damaged cells, and the insect dies. They have no residual action and easily wash away. This is what makes insecticidal soaps a safer pesticide option compared to traditional pesticides. This also means, however, that insecticidal soaps have to be applied frequently to control insect populations as they only affect the insects they come in contact with. Any hiding insects or those that emerge after the application would be unaffected and would require a second (or third, etc.) application to kill them.