But now a new study published Tuesday in the Journal of Economic Entomology says it might finally have a straightforward answer: Get the psyllids high. No, not on drugs. Get them to higher elevations. The tiny, invasive bug from China doesn't fare well at elevations of 500 meters to 800 meters above sea level, the study says.
The study was conducted in Puerto Rico, "which has variations of elevations with citrus which Florida does not have," said David Jenkins, a U.S. Department of Agriculture research entomologist at the Tropical Agricultural Research Station in Mayaguez. "We found the psyllid at all sites below 600 meters but none above it. At 500, we had a high level of psyllids. If atmospheric scientists can somehow duplicate conditions near the trees, the psyllid could be controlled," said Jenkins, a co-author for the study.
At this point, Florida and California growers and agriculture officials are about ready to try anything. Huanglongbing has caused billions of dollars in damage to citrus crops. It's been detected in Georgia, Louisiana and Texas, and has mutated into strains that are now in Africa and Latin America, including Mexico and Brazil.
There's no cure, even though more than $80 million has been poured into research, and 500 scientists from 20 countries who attended a 2012 conference in Orlando came up with nothing. If the problem keeps up, it could be the end of plentiful orange juice. You heard right -- the long-shot, worse-case scenario is the supply of orange juice could be reduced to a drip.
“What’s at stake is orange juice on the breakfast table,” Michael Sparks, chief executive of Florida Citrus Mutual, a trade association, said last year after the state announced that half of all its citrus trees were diseased. “I don’t want to indicate that’s going to happen next year. With a 10-year decline, your supply will reduce.”
Two years ago, David Hall, another USDA researcher who co-authored the study, heard that citrus psyllids couldn't handle heights in China and Mexico. That theory hadn't been proved, so federal researchers set out for Puerto Rico, where the bug has spread, to conduct some experiments. They chose 17 sites with mostly Valencia orange and lemon trees at elevations from 10 meters to 880 meters above sea level and baited trees with sticky yellow traps.
For two years, they watched. The higher the presence of citrus psyllids, the more they found in the traps. "There was a strong trend in both years for decreasing psyllid abundance with increased elevation based on the number of psyllids captured on traps and the proportion of trees shown to be infested," they wrote. "No psyllids were collected at an elevation of (more than) 600 meters."
Why should Florida and California's state entomologists and citrus growers care? Florida provides about 80 percent of the nation's orange juice, worth about $9 billion per year. Brazil chips in the other 20 percent. California produces a third of the nation's citrus, and is the leading grower of lemons.
If psyllids gasp for air at higher elevations, it means something is happening in their itty-bitty chests. Or, more likely, the conditions change compounds in plants the bugs eat, making them less tasty. "Changes in elevation result in changes in temperature, short-wave radiation, partial pressure of respiratory gasses, precipitation, oxygen content, and air pressure," the study said.
"If any of these can be shown to affect the development of the Asian citrus psyllid or of citrus greening disease," the authors said, "then it may be possible to induce these conditions in citrus trees at lower elevations."
Or, there's a simple, more straightforward approach: "Another practical implication for this study would be to put citrus nurseries above 600 meters," where the bugs struggle, the study said. It's just a suggestion, the authors said.
Florida researchers are listening, Jenkins said.
"In fact some people in Florida have contacted us," he said. "They want to conduct studies with pressure, as far as pressurizing tree. They’ve got atmospheric scientists looking at that kind of stuff. We’re not the ones that have the ideas on how to use it, but somebody out there may have the idea to make this practical."
It gets better. Earlier studies have shown that the eggs of cold-blooded insects take twice as long to develop into adults for lack of warmth. Nothing likes a slow developing psyllid nymph more than parasitic wasps that attack nymphs, sting them and lay eggs that feed on them from within until they burst from the skin like something out of the movie "Alien."
"That's exactly what happens," Jenkins said, excitement in his voice. "It's incredible."
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