So it's the end of February 2008, when I realize my potted plants are under attack by the thrips. I knew enough to identify their tiny, dark, cigar-shaped bodies, but that's about it. What the hell are the thrips!? It sounds like a 19th century frontier disease, like pleurisy, the shingles, the gout, or the piles.
Thrips (Thrips, Heilothrips, Dendrothrips, Taeniothrips, etc.)are very small insects found nearly worldwide. They sorta' look like ants with an elongated abdomen, stubby legs, and fringed wings typically folded on top of the abdomen. Of the 600 or so species in America a few are beneficial carnivores feeding on mites and other small insects.[1] But the overwhelming majority are deleterious herbivores damaging leaves, stems, flowers, and fruits of many plants. (Thrips is both singular and plural. "Thrip" is incorrect in any usage.[2])
Thrips are like tiny Insecticons, Decepticon robots that transform into insects and munch through buildings, spaceships, and Autobots. Or better yet, they are like the microscopic, metallic bugs that comprised GORT in the 2008 version of "The Day the Earth Stood Still": numerous hordes bent upon destruction.
They use their rasping mouthparts to scrape away the outer cell walls of plants causing them to rupture and leak. The thrips then drink the nutritious sap. The constant scraping causes scarring and discoloration on the damaged leaves. They hide on the undersides to avoid predators. By the time thrips are visible on tops of the leaves, they have reached infestation stage and the plant is in serious trouble. It is literally death by thousands of tiny cuts. Out of control populations (like on my amaryllis, crinum, and ludisia) can completely drain leaves of chloroplast, which starves the plant into dormancy or death.
Spotting even one is consequential, as thrips multiply like wildfire, and some can reproduce asexually. Eggs are laid in leaf tissues. The young hatch ready to feed. Thrips do not go through a metamorphosis, such as caterpillar-to-butterfly or maggot-to-fly. Like grasshoppers, their young (instars) resemble small adults and feast on plant sap too. Before reaching maturity, the instars drop to the ground and pupate. When they emerge from the pupae, thrips are mature adults capable of reproduction and flight. [Alas, I did not know this last summer, so many of my eradication efforts failed because I did not account for the pupating adults in the soil.]
Young thrips have limited mobility. However, once they can fly, their reign of terror truly begins. They are weak flyers but more than capable of navigating a home or greenhouse. They spread from plant to plant and pot to pot with the same visual symptoms. Plant vigor is reduced and growth is stunted. Ravaged leaves have discolored patches and brown spots (fecal stains). Older leaves develop bronze or silvery streaks while younger leaves are often physically distorted. Flowering is halted and buds drop. If unchecked, wilting and leaf drop are the next phases.
Many die from this direct assault. Just as insidious are the indirect assaults from disease vectoring. Thrips spread many viruses. Last summer they spread red blotch to nearly every amaryllid (daffodil family member) that I grow, including: Crinum, Hippeastrum, Ismene, Zephyranthes, Sprekelia, Nerine, and Chlidanthus. In a nutshell, thrips are plant killers and garden terrors.
GI Joe says, "knowing is half the battle." Now, for the other half. How do I stop 'em?
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