Bugs duped into spreading citrus plant disease

Chuck Bednar for redOrbit.com – @BednarChuck

A bacterium believed to be responsible for a deadly disease affecting citrus plants purportedly assists with its own spread by “hacking” the behavior of insects, researchers from the University of Florida and their colleagues explained in a recent PLOS One study.

According to BBC News, the disease called citrus greening or huanglongbing has had a drastic impact on the appearance and overall health of orange and other citrus plants. The condition is being spread by an insect known as Asian psyllids, and the new research shows that when those bugs feed on infected plants, they fly farther and more frequently than usual.

This improved mobility is believed to improve the chances of the insect passing the pathogen on to other plants. They told the British news outlet that they hope their work will lead to the development of new ways to help control and combat citrus greening disease.

When a plant is infected with the bacterium, “the leaves start to yellow and [grow] mottled in appearance, the branches begin to die back, the root system dies back and ultimately the tree declines and dies,” Dr. Kirsten Pelz-Stelinski, corresponding author on the new study, told the BBC recently. “It’s a global problem in terms of citrus production.”

Chemical attraction tricks psyllids 

The disease, which has infected oranges, grapefruit, and lemon plants, is believed to be caused by a group of related bacteria, including the strain focused on in the study, Candidatius Liberibacter asiaticus (CLas). Once the microbe enters a citrus plant, it begins to replicate in the sap, which transports nutrients to different parts of the plant.

To spread, it uses the Asian psyllid as a carrier. The insect feeds on the citrus planet through its proboscis, a special tube that it inserts into a leaf to consume the sap. If it feasts on a plant infected by CLas, it can also become infected with the bacteria, and when it moves onto another plant to feed, it can spread the disease.

“We know from some of our previous research that psyllid insects are particularly attracted, at least initially, to plants that are infected with the pathogen,” Dr. Pelz-Stelinski told BBC News. Plants that contain the bacteria produce a substance known as methyl salicylate, which psyllids are attracted to. However, the chemical’s affect on the insect is said to be short-lived.

“When the bacteria’s present, the psyllids feed and the volatiles are released, but the psyllids will realize that this is maybe not the most suitable host plant, and we think that’s because infected plants tend to have lower nutritional quality,” she explained. “So the psyllids will move from that infected plant to find a new host and when they move they take some of those bacteria, so the bacteria are promoting their own spread.”


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