Spring is still a while away but soon it will be that time of year again. All sorts of bug eggs will hatch and the youngsters will show up on our bonsai to feast on the spring sap. Of course, you can then take all sorts of measures to make your bonsai less attractive for these critters. But perhaps it is best to prevent large scale outbreaks?
To have fewer problems with sucking insects in early spring one can consider using horticultural oil. This dormant spray is a light oil-based product that is sprayed on trees while they are dormant.
The oil forms a thin layer all over the plant and any eggs trapped below them will slowly suffocate. An added benefit: It will also kill off any scale insects left on your tree. Do note.. It is non-discriminatory: It will also kill off the eggs of beneficial mites and insects. This is why I only use it on my bonsai, and very limited on other fruiting trees in my yard. I prefer to keep the natural ecosystem intact. But I do dislike them suckers on my bonsai. As this oil can lead to leaf burn it is only used in winter during dormant time. Then also on evergreens the risks are limited (But not absent, so test before spraying the whole plant!)
I typically spray on frost-free days with clear winter weather. In case of rain there is a risk of the product washing away to quickly. Prepare the product as indicated on the package. Typically, this will be something around a 1:50 or even 1:100 dilution. Subsequently you spray the whole tree and spray it dripping wet ensuring the whole tree is covered. Done. That took all of five minutes!
Of course there are several products available for sale. Just check your favorite garden center or online trader for options.