Treehoppers, or thorn bugs, are wedge-shaped, sap-sucking, jumping insects found everywhere on Earth except Antarctica.
All treehoppers have conspicuous eyes and modified dorsal plates (pronotum), commonly called helmets. These helmets are believed to have evolved from what was once a third set of wings. Frequently, these helmets look like camouflaging thorns. [Many thorn-shaped tree hoppers will shimmy around to the opposite side of a stem as you walk by!] Globally, the range of treehopper shape defies description. While most colors are drab, you can also find neon stripes, spots, and squiggles. There are treehoppers that look like ants walking backwards, space ships, curls of dry wood, flower petals, and even bird poop! Nymphs can be equally bizarre, donning such crazy outfits as a puffy cotton bodysuit, a head piece of neon spikes, or a tail made out clusters of el-wire. (Check out more pictures of treehoppers at Mental Floss.) Most treehopper nymphs have Mandelbrot spikes on their helmet. North American treehoppers are far less flamboyant. They tend to be green or brown, smooth-bodied wedges, 1/2 inch long or shorter. In the greater Bay Area, we have Oak treehoppers (Platycotis vittata) and Buffalo treehoppers (Stictocephala bisonia). Oak treehoppers are commonly found in spring, in the lower branches of oak, birch, and other deciduous trees. Buffalo treehoppers can be found in apple trees.
Ants and treehoppers
Just as ants protect and farm aphids, they provide similar mutualistic services to treehoppers. Being sap eaters, treehoppers poop out a sugary waste called honeydew. Ants love to eat honeydew. The relationship is so intimate that treehoppers can send out an alarm when they are attacked and ants will come to their rescue! Some species of treehoppers have the same type of relationship with certain wasps and even geckos!
Eggs are normally inserted into the cadmium layer of stems by a female’s saw-like ovipositor. Sometimes, eggs are laid on leaf surfaces. Many plants are damaged more by egg laying than by treehopper feeding. When eggs hatch, the nymphs are usually too small to produce enough honeydew to attract ants. Some mama treehoppers will stay close by, using her honeydew to attract protective ants. Unlike adults, nymph treehoppers have an extendable anal gland used to deposit honeydew further away. These tubes tend to be longer in solitary treehopper species. I wouldn't bring it up except that this appears to be an important evolutionary mechanism for avoiding infection by fungal diseases, such as sooty mold.
Damage and host plants
Treehoppers have sharp beaks they use to pierce grass blades, twigs, canes, leaves, and branches. As sap oozes out, treehoppers lap it up, taking advantage of the high sugar food source. As treehoppers feed, they can act as vectors for disease. In fact, some treehopper diseases attack both the pests and the host pants, growing in the treehopper’s salivary gland! Predominantly a tropical pest, treehoppers can still damage your grapes, celery, tomatoes, legumes, avocado, and papaya in North America. Their cousins, the leafhoppers, cause far more damage to our local gardens.
In nature, treehopper eggs are frequently parasitized by fairyflies (Mymaridae) and Trichogrammatidae. For this reason, it is better to avoid broad-spectrum pesticides. Horticultural oils can be used to prevent eggs from hatching, and insecticidal soaps can be used to treat heavy infestations of nymphs and adults.
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.