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Ask An Entomologist @BugQuestions
, 12 tweets, 4 min read Read on Twitter
For our first #DeepDive since our hiatus, let's talk about a disease that we'll be hearing *a lot* about in our near future: Huanglongbing, or Citrus Greening disease.

Specifically, how do we know the disease even exists?
The inspiration for this one comes from an activist group who was trying to spread the idea that Huanglongbing (HLB and/or CG from here on out) was predominantly caused by herbicide damage.

HLB was first described in Western science journals in 1919.

However, farmers in China had known about the disease for several generations and had called it 'Yellow dragon disease' and the earliest written records dated back to the 1870s.

It was likely known even before that.
In the 1950s, it was discovered that the disease could be transmitted through grafting (note: this can't happen w/H-cide) damage.

In this case, it's as simple as putting a leaf punch from an infected plant into a clean plant.
The next big step in HLB research happened in the 1960s, with the identification of the pathogen through Electron Microscopy.

At first, HLB was thought to be a virus...but EM (like the pictures below) showed the veins of the plant blocked by bacteria!
After this, the next big breakthroughs all happened in the 1990s:

1.) Sequencing allowed us to find bits of DNA from the pathogen which allowed us to diagnose the disease rapidly

2.) The first antibodies were produced that let us ID the bacteria via unique proteins
These two breakthroughs were huge, because they allowed us to diagnose the disease not only in the Citrus plant, but being able to detect DNA allowed us to figure out the vector in the mid-2000s.
We can use these tools to answer questions like "Where do these bacteria live inside the insect?"

It turns out that they hijack the parts of the cell where proteins are made to make protected houses inside the cells.

Red-stained antibodies highlight the bacteria in pic below.
So what challenges do we have with HLB research?

Well, for starters, we can't culture the bacteria from infected plants.

So all the experiments that scientists do look a lot like this.
There's also a lot of problems finding infected trees.

There's a lot of abandoned orange groves, and many people who have ornamental Citrus in their yards don't test their plants.

So there's HLB bacteria all over the place.
...but there's also a lot of new tools coming up.

These include:

1.) Citrus orange trees which have been transformed with anti-HLB proteins from spinach
2.) Vectors which have been inoculated against the disease and sterilized using Wolbachia bacteria
This isn't going to be a one-tool solution, not like what happened with Icerya purchasi back in the day.

We'll need to efficiently detect the bacteria in real-time, as well as find new ways to fight the bacteria as we find it.
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