A thrips (no, that’s not a typo—there’s no such thing as a thrip!) is a bizarre, minute insect. They are typically less than 1 mm long with slender bodies, fringed wings and weird lopsided mouth parts.
Like most damage from sucking insects, you will see yellowing or spotting on leaves and flowers, stippling, or distortion of fruit. Some thrips are predators causing them to cross the line over to “good bugs”. However, they can also harbor the tomato spotted wilt virus that will further weaken the plant.
They are most active during hot and dry seasons but can be seen year round in many areas.
These can be found on all continents (except Antarctica, of course) but are most prevalent in temperate and tropical locations.
Thrips prefer warm and dry conditions which are often present during growing seasons. They also thrive on growing tissue, so tomatoes are a prime candidate especially when they are seedlings.
Sanitation, sanitation, sanitation. Make sure weeds are not hiding in your garden and if you suspect a plant is infected, remove it! Horticultural soap sprays are a good next step if populations have gotten out of control before moving on to toxic chemicals. You can make soap solutions at home but these are often too strong so a commercially available soap is recommended. There are also many beneficial insects available commercially that feed or parasitize these little buggers.
Though thrips can cause cosmetic damage, crop yields are generally not greatly affected these insects. Make sure to keep that in mind before taking any drastic action against them as you may adversely affect the local beneficial populations causing larger outbreaks in the future.