What are scales and mites?

Scales [Coccoidea family] are small insects that mainly survive by parasitically feeding off of a plant's life sustaining sap. But there are some scale insects that specialize in fungal food sources.

Mites [Acarina subclass, Arachnida class] are even smaller than scale insects. In fact, many of them only can be seen with a microscope or magnifying glass. They too are parasitic feeders. Depending upon the mite, the food source may be plant, mold or animal. Despite the generally destructive tendencies of mites, some actually are considered beneficial insects. Specifically, predatory mites eat other mites.

Aphids [Aphidoidea superfamily] tend to be green. But different aphids may be black, brown or pink. They're considered among the most destructive pests of edible plants. One reason lies in their tendency to make the plant sick with viruses at the same time that it takes away the sap that could help the plant fight the sickness. Many of them tend to focus on one kind of plant as a food source. But the green peach aphid [Myzus persicae] isn't picky, and basically considers any plant as a food source.