Thrips are tiny insects that are usually yellow, tan or black. They damage plants by sucking juices from leaves which in turn cause yellow pale spots and leaves will curl.
In severe infestations, especially with Ficus nitida - a commonly used street tree, leaves will turn yellow and die. Thrips thrive in hot dry summer-like conditions.
Minor thrips infestations can be handled with a strong blast of water and feeding the plants. Otherwise, you may have to break out the insecticidal soap or a ready-to-use natural control like Captain Jacks Dead Bug Brew.