Greenhouse Thrips

Life in a greenhouse can be idyllic if you are a seedling, whitefly, or a thrips.

The same conditions that provide for optimal plant growth also create a perfectly protected habitat for pests, such as greenhouse thrips. Of course, those pests then escape their Eden and end up in our gardens.

Greenhouse thrips, multiple life stages (Whitney Cranshaw, Colorado State University, Bugwood.org) CC BY 3.0 US

The thrips family is huge, with thousands of varieties worldwide. Most of them are pests, sucking sugary sap from leaves, buds, and stem tips. But the insects themselves are very tiny (1 mm long or less). In most cases, you will see the damage they cause before you see the actual insect.

Invasive greenhouse thrips (Heliothrips haemorrhoidalis) are also known as glasshouse or black tea thrips. They were originally from Brazil but are now found pretty much everywhere except extremely cold regions.

Greenhouse thrips damage

These pests prefer perennials with thick, broad leaves, which means their diet often includes avocado, bay laurel, and citrus. They also feed on coffee, guava, kiwifruit, macadamia, pecan, stone fruits, and stone pine, along with several ornamentals, including azalea Grecian laurel, rhododendron, and St. John’s wort.

Feeding punctures result in stippling that can expand to create whitish-gray areas on leaves, reducing plant vitality. Severe infestations can cause defoliation. You may also see leaf curling and cupping. These pests can carry tomato spotted wilt virus. The biggest problem with thrips feeding is the scarring, cracking, and lesions they cause on fruit.

Extensive thrips damage to leaf (Swapnil Karambelkar) CC BY-SA 3.0

Coffee tree leaves curling in response to greenhouse thrips feeding (Smartse) CC BY-SA 3.0

Greenhouse thrips identification

Adult thrips have black bodies with white legs and wings and yellow bellies. Their wings are not well-designed for flight, being fringed hairs instead of membranous panels. To move quickly, thrips use a cla p-and-fling method which is why you may suddenly see something shoot by as you work in your garden.

​Greenhouse thrips have heads and jaws that are sideways and somewhat backward. I have no idea why. The technical term is ‘hypognathous head’.

Larvae and pupae are really tiny. You could place 35 of them, end-to-end, across an American dime. Using a hand lens, you would see that they are white to pale yellow with red eyes. You may also see a blob of green poop (frass) on the rear end of larvae. Scientists believe this is used to deter predators. I’ll bet it works, too! Eventually, that frass falls off. If you see tiny black flecks on the underside of leaves or caught up in fruit clusters, it’s probably greenhouse thrips.

Greenhouse thrips lifecycle

Thrips nymph (M. J.) CC BY-SA 2.0 de

As far as we know, there are no male greenhouse thrips in California, which might sound like a good thing with regards to pest control, but it has no effect on the local thrips population. Thrips can reproduce through something called parthenogenesis, which means fertilization of the ovum is not needed to produce baby thrips. Each female lays up 60 eggs in her lifetime. Those eggs are inserted into fruit or leaf surfaces. As they grow, they can create a swelling known as an egg blister. Four to five weeks later, those eggs hatch, and larvae start feeding. There are usually five or six generations each year, but there can be up to twelve generations if conditions are good. That ends up being a lot of thrips.

Robber fly eating a thrips (Shyamal) CC BY-SA 3.0

Greenhouse thrips management

These pests, like many others, have developed resistance to insecticides and spinosad, so don’t bother. Instead, put nature to work for you. Natural predators, such as robber flies, will put a dent in thrips populations. If thrips are a serious problem in your landscape, you can buy predaceous thrips and you may be able to find egg parasites, such as Thripobius semiluteus or Megaphragma mymaripenne, that you can release in your landscape. Cultural thrips controls include thinning fruit to reduce hiding spaces (and improve fruit quality) and harvesting fruits as soon as they are ripe.