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Remember when I wrote about Panama disease, the fungal blight which is coming for the Cavendish bananas (after laying waste to the Gros Michel cultivar bananas back in the 50s)? Well, sadly, Panama disease is not the only apocalyptic fruit blight on the international circuit these days. It turns out that a bacterial disease is destroying citrus groves around the United States and beyond. The disease, known in English as “citrus wasting disease” is caused by a motile bacteria, Candidatus Liberibacter, which is spread by the Asian citrus psyllid (Diaphorina citri), an inconsequential Hemipteran insect which lives in citrus groves. There are multiple strains of greening disease, and there have been for a long time, but the newly problematic strain originated in China where it is known by the evocative name “huánglóngbìng” which means “Yellow Dragon Disease.”
A revolting Asian citrus psyllid, Diaphorina citri
The wild ancestors of most of today’s grape fruits, oranges, and lemons, came originally from the forests of East and South East Asia so it is not a huge surprise that this horrible disease comes from there too. Unfortunately hemipteran insects can easily proliferate in new ecosystems, so the disease became a problem after these invasive insect pests gained a widespread foothold throughout the semi-tropical regions where citrus is grown.
A tree infected with citrus greening disease
Citrus fruit is delicious and wonderful beyond compare…so it is worth big money. This means that agricultural scientists have been studying huánglóngbìng and attempting to stymy it with medicines, pesticides, and transgenic tinkering. The scientists themselves have been hampered in their research by the fact that it is hard to maintain and study citrus plants infected with the disease because they die so swiftly (the infected citrus plants, not the agricultural scientists). Powerful antibiotics work to wipe out the disease, but it is not practical to give these medicines to trees (though we will probably try—with predictable results). Scientists feel that there may be a transgenic solution, but it is unclear how marketable such a chimera will be (since protectionists and Luddites have been fear-mongering pretty hard against GMOs).
This leaves mass application of insecticide as the best bulwark against huánglóngbìng. It is starting to seem that small orchards and groves which are unwilling to commit to this kind of regimen will soon be gone. All of this strikes me as unbearably sad and frightening. Why are there so many blights everywhere? Has this always been a peril of agriculture (indeed of life?) or has contemporary monoculture paved the way for widespread proliferation of these superbugs? There must be some parasitoid wasp or something which has kept these damn psyllids from wiping out species citruses of wild Asia. Maybe we could bring that here…but it probably would cause some new horrible problem.
We’ll keep you posted. In the meantime you should glut yourself on oranges this winter…while you still can.
I’m going to expand upon yesterday’s post about invasive animals in Florida. Pythons are indeed large aggressive predators, but it isn’t as though they chose to move to Florida like Aunt Edna when she retired. Enthusiasts brought them from Burma. The pythons escaped or were set free and they found a way to survive.
Florida’s groves of tasty, tasty oranges are hardly natives either. Over long centuries, Spaniards carefully hybridized trees that bore perfect sweet fruit. They then carried saplings across the oceans from the fragrant orchards of Iberia.
Fresh-squeezed, Ice-cold, Juicy…what was my point again?
We humans are ourselves an invasive tropical species from Africa. As we have explored the world, we have encountered all sorts of useful and interesting plants and animals. Thereafter we took those friends with us. Dogs, ducks, and dairy cows, roses, rye and rice–all of our favorite living things are invaders of a sort. Sometimes we make bad or dubious friends (pythons? really?) but our existence depends on the grains we harvest, the fruit we grow, and the animals we farm. Such is the price of our success. If we all returned to fishing, hunting, and gathering, we could expect to remove three or four zeros from our total population number of six billion.
The story of invasive species however extends far beyond humankind’s symbiotic alliances and restless propensities. A couple of quick examples will clarify this point. Like the pythons, Florida’s native manatees have a great deal of trouble with cold weather. Every winter, many starve to death in the warm outflows from power stations where they shelter (or they freeze outright). They must have expanded their range northwards as the ice ages ended. The armadillos that live on the panhandle are edentates who began trekking out of South America during the Pliocene (3 million years ago) when the Ismuth of Panama formed and rejoined the sundered Americas.
This story goes on and on and gets bigger and bigger: flowering plants showed up from elsewhere, so did mammals and reptiles back in the Paleozoic Era. In fact, if you go back far enough all life-forms are invaders.
Well, maybe some of us...
ferrebeekeeper 