Bug Day (2): Spittlebug

Meadow Spittlebug (Philaenus spumarius)
Spittlebug nymph foam microhabitat

Few park visitors ever notice the Meadow Spittlebug in its adult form, as in the photo above taken by sharp-eyed naturalist Jutta Burger. What we commonly see is the foam bubble that serves as home for the newly-hatched nymphs, as in the next photo. The mother bug has up to 400 eggs to lay. She glues them to a great variety of plants — this bug is famous for its catholic tastes — in small groups in the autumn. The eggs remain there over the winter. In the spring, the nymphs emerge and start sucking the sap from the plant. The nymphs hang upside down and from an anal gland secrete the foam that cascades down to surround them. Each nymph can excrete spittle each day equivalent to 150 times its body mass. The spittle makes up a microhabitat that provides moisture and concealment. It also dims the sunlight to which the nymphs are sensitive. They go through five moults or instars before the foam dries up and they emerge as adults. Adults do not make foam but roam freely. The females mate soon after emerging from the foam, and the cycle continues.

The spittlebug comes in a great range of colors and color patterns. These color variations and the DNA variants that determine them have occupied scientists for decades.

The spittlebug has powerful hind legs that allow it to leap quickly. The feet on its jumping legs have tiny spikes tipped with zinc, like a human athlete’s metal-spiked shoes. Because of its jumping prowess, this bug is sometimes called the meadow froghopper. The adult spittlebug accelerates to 408g (multiples of the force of gravity) at takeoff. (Military jet pilots with protective suits may experience up to 9g.) A study concluded, “For their size, froghoppers outperform other insects: they exceed the height jumped by the flea relative to body length and accelerate their much heavier bodies four times faster.” The spittlebug jumps with so much force that the human ear may be able to hear a thump as it launches. It can also walk (when it just drags its jumping legs) and it can fly.

Farmers, gardeners, and scientists have studied the spittlebug for a century. It has been shown to eat more than 500 different plant species. Each nymph can suck up to 280 times its own body weight in sap per 24 hour period. Farmers have complained that it has damaged alfalfa, red clover, wheat, oats, corn, and strawberries, among others, sometimes in economically significant amounts. But this bug has captured headlines in recent decades as host to and carrier of Xylella fastidiosa, a bacterium that can damage plants much more severely than the insect’s nymphs. It has been called one of the most dangerous plant bacteria in the world. Notably, the X. fastidiosa bacterium is a mortal threat to olive trees.

The introduction of the Xylella fastidiosa Wells bacterium into Apulia (South Italy) has caused the massive dieback of olive trees, and is threatening olive production throughout the Mediterranean Region. The key vector of X. fastidiosa in Europe is the spittlebug Philaenus spumarius L.


An article in Wikipedia elaborates:

The disease is particularly affecting olive groves in Southern Italy. It was first detected in Italy in 2013,[2] in the Salento Peninsula; by late 2013, it was estimated that approximately 8,000 hectares were affected.[3] The disease currently threatens olive groves and oil production in Italy, Greece, and Spain, which together account for 95% of European oil production[4][5] One 2020 model predicts a potential economic impact of the disease for Italy over 50 years between 1.9 billion to 5.6 billion Euros.[4]

In addition to Europe, the disease has also been detected in olive crops in California, Argentina and Brazil.[6]

An olive grove infested with Xylella fastidiosa in Puglia, Italy in 2019. Photo Wikipedia.

Although they are considered relatively poor fliers, spittlebugs can manage to fly 1000 meters (0.62 miles) in an hour. That was enough to spread the olive die-back disease northward in the Apulia region of Italy at the rate of 20 km (12.4 miles) per year. The bacterium can also kill almond trees. An outbreak in Alicante, Spain in 2017 forced a shutdown of almond groves covering about 350,000 acres. Cases of the almond leaf scorch disease, cause by this bacterium, have been found in California. Grapes also are vulnerable to the bacterium; it causes Pierce’s disease, especially in areas with mild winters. Other insects, notably the glassy-winged sharpshooter (Homalodisca coagulata) also carry the deadly germ, which may damage citrus, peaches, plums, coffee plants, oaks, oleanders, and others. Many plants may host the bacteria without showing symptoms; the spittlebug and a few similar insects may acquire the bacteria from such asymptomatic plants and then transmit it to other plants that are more vulnerable. Sound familiar?

The use of insecticides against the spittlebug has knocked out some high concentrations of the insect but had little long-term effect in reducing the populations in Italy. Many measures have been tried to combat the bacteria on a living plant, but nothing has shown effectiveness to date. Fortunately none of the plants in or near Cesar Chavez Park are on Xylella fastidiosa’s target list. The bacterium has no effect on organisms other than specific plants.

Birds are the plants’ best friends when spittlebugs appear. Many species of birds take and eat adult spittlebugs, and some feed on the nymphs. Spiders also take the adults, and some ants attack the nymphs. One species of fly, the Verralia aucta, and a species of nematode, attack the spittlebug adults, and there are fungi that attack both the adults and the eggs.

The female spittlebug is polyandrous; it mates with several different males throughout the season, meaning that the eggs it lays come from different fathers. This DNA diversity may increase the bug’s versatility in adapting to different environments. But there are limits. The spittlebug requires at least a moderate amount of moisture in its plant hosts to create spittle, and cannot tolerate sustained hot drought conditions. A recent UC Davis study found that these insects have declined rapidly along the California coastline, and have disappeared from some of their former habitats, hypothetically due to rising average temperatures. But a study in the UK found that summer drought and increased temperatures there had no effect, or even a slight positive effect, on the population of these insects.

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