Thrips can be found in the US and Canada in your veggie patches. The larvae is so small that you hardly know they are present until you see signs of damage on young plants.
Thrip larvae magnified
They are the sucking variety insect. The moth is only 2mm long and is light yellow to brown coloured. They have two pairs of hairy wings.
Adult Thrip (top left)-W.L. Sterling, Texas A&M University, Adult thrip (top right)-Integrated Pest Management, Lifecycle (bottom)-University of Vermont Entomology Department
Thrips overwinter as larvae in discarded onion remanants, alfalfa and clover. They emerge in the spring to become moths which then lay their eggs on host plants. They are so small that the wind may carry the larvae from garden to garden. In the feeding stage you will find them eating or rather see their damage first.
Thrips on onions (top left) & (top right)-Jack Kelly Clark, Damage on Onion (bottom)-Integrated Pest Management
Diet and Damage
Onions and garlic (Allium Family) are their favourites but they will also do serious harm to cole plants, parsley, curcubits, beans, lettuce and celery. I have also had them on my gladiolia as well, so they seem to like them too. They are a most destructive pest. If you see whitish blotches on your crop foilage then you know that you have this pest. They are so small you need to see them with a magnifying glass. Sometimes injury is so severe that that leaves curl upward. Plants will wilt and die. Onions will curl up and die. Very heavy rainfall can also help control this pest. Some farmers in Canada have had infestation so servere that they actually flood their fields to control thrips.
1) Soap or Herbal Extract Sprays
At the very first sign of these guys spray your foilage well every few days. Wormwood, tansy, lavender or sage can be added to the soap spray. Boil them, strain and add this to your soap. It works quite well.
2) Full Garden Clean Up
Remove all garden debris, expecially onion skins. Thrips are attracted to debris in protected areas to overwinter. 3) Keep Weeds Down
Make sure weeds are not a problem on the outskirts of your garden. Thrips sometimes hide there or are blown from another garden.
4) Grow Healthy Plants
Weak plants are prime targets for the thrips to get started so try and make sure that all your plants have the necessary nutrients.
5) Yellow Sticky Traps
Make a few of these traps and place around your onions. With a small fan you can blow the thrips onto the traps.
A hard spray of water will knock them off and drown them.