Lard Greystoke

A very cheap method is to dilute some detergent or liquid soap in water, spray on all surfaces of plant. Eliminates surface tension of water, overcoming waterproof covering of bugs' respiratory systems, drowning them. Has no residual effect so you have to keep doing it. Could damage waxy layer covering leaves, causing discoloration.

A warning on diatomaceous earth: it will "slice and dice" the inside of your lungs same as bugs' exoskeletons, so be careful not to inhale.