You've probably never heard of huanglongbing – unless, of course, you're a citrus farmer. Then you'd know that it's another name for citrus greening disease – a tree affliction brought about by the Asian citrus psyllid, a pinhead-sized insect. To fight the blight, researchers have decided to appeal to the bug's romantic side by creating a trap that lures it in by playing the sound of a female psyllid.

Huanglongbing is a bacterial infection transmitted by the psyllids that causes trees to often bear strangely-shaped green fruit that produces a juice that tastes acidic and isn't commercially viable. Because of concerns about combating the insects with pesticides, entomologist Richard Mankin decided to try another approach to eliminate the critters. Mankin works for the Agricultural Research Service, a division of the US Department of Agriculture.

Together with a group of graduate students from the University of Florida, Mankin developed an acoustic trap that plays upon the way in which male and female psyllids signal each other. This begins when the male rapidly vibrates his wings to send vibrations through the branch of the tree on which he is perched. Any nearby females that are interested in this sonic advance would send back a wing buzz about a half-second later that would draw the male to her.

An example of a tree afflicted with huanglongbing, or citrus greening disease(Credit: Tim Gottwald)

Mankin's device intercedes by sending an artificial female signal back to the male one tenth of second sooner than the actual female insect responds. This directs the male towards the artificial sound, which has a sticky surface that traps and kills the bug.

The trap consists of an Arduino microcontroller that has a buzzer and microphone attached to it. When the mic picks up the male bug's vibrations, the processor causes the buzzer to activate creating the false signal and luring the bug toward the trap.

"The microcontroller system runs on battery power, and can go for about five days now before it runs out of juice," Mankin told Gizmag. "The whole system is attached to an outer branch of the citrus tree. It is slightly larger than a three D-cell battery pack. It's fun to watch the male wandering around the branches trying to find his potential mate! We're still trying to reduce costs and battery usage, but the system has been tested already in some local orange trees."

The trap will continue to be field tested this summer, and the researchers will strive to get the system down below a price tag of US$50. If they're successful, the trap would likely become part of a multi-pronged approach to battle the psyllids and halt the crop-damaging spread of huanglongbing.

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