Most insecticides used by commercial growers are very effective and wash off with soap and water. That is why fresh fruit is washed before it is bagged and shipped. Use the link below for the CA Coop Extension Services center near you. Their job is to tell you which sprays will work for you. If they don't have the answer, they should give you a contact in the commercial citrus growing CA counties who will have the infromation. In addition, I suggest you use a broad spectrum insecticide to spray all of your ornamental shrubs, trees and lawn to get rid of the recurring pests. You may need to spray and wait two weeks and spray again to get rid of the pest and the hatchlings that come after them. After that you should be good for 60 days before spraying again. It will depend on the amount of rain as to how often to re-spray. Ask your cooperative agent about this as well.

Here is a link that might be useful: Coop Ext Services - CA

Using a broad spectrum pesticide around your entire yard is folly. These chemicals take out the good guys! It's a healthy, normal population of beneficial critters that keeps the bad guys at bay. It's well documented that the use of such pesticides often cause a population explosion of the PESTS later on in the season. That is where the adage comes from: "the more you use pesticides, the more you HAVE to use them". As a matter of fact, ceasing to use such chemicals will help to stop the pest outbreak.

Another thing to think about is that contact pesticides (non-systemic) aren't particularly effective against scale insects. Your best options are likely to fall in the horticultural oil category. There are many such products available for use.

Seeing pest insects is normal. A healthy yard and garden will always have a population of mites, aphids, scale, and other pests. That's what supports the much larger population of predators and parasites. Foster a well-balanced yard and you shouldn't have too many problems.

The one critter that you may need to manage is the ant, if they decide to work against you. Some ants can cause aphids and scale populations to increase because they (the ants) will defend their little honey-dew producers against their enemies.

You've planted ONE dwarf Meyer lemon tree. You will always be able to prevent major pest outbreaks by keeping an eye out on the tree, by identifying the critters you see, by occasional (well-timed) applications of benign oils, insecticidal soaps, and other products. Make sure that your plant is healthy (which does not mean over fertilized).