There is a little critter called the Asian citrus psyllid that potentially carries a Chinese citrus greening disease called huanglongbing. It has decimated Florida citrus crops and now, has, shown up in Los Angeles and Kern Counties. Not every psyllid is a carrier, but, the disease cannot spread without the pest. The psyllid transmits the disease by feeding on the liquid inside citrus leaves.
Psyllids have now been found in the city and last weekend, November 2015, there was a lot of spraying going on in our neighborhood. We don't have citrus, but, our neighbors do.