Using insect viruses to combat the Asian citrus psyllid
Article written by Elizabeth Grafton-Cardwell, Peggy G. Lemaux, & Lukasz Stelinski.
Revised May 8, 2017
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Insects have viruses just like people have viruses. In fact, viruses are the most abundant microbes on our planet. Most viruses are discovered only when they cause disease in their hosts. An example is the human immunodeficiency virus (HIV), the pathogen that causes AIDS. This virus is not new, but has existed for thousands of years in its natural host, most likely non-human primates, where it did not cause disease. It remained undiscovered until it shifted to humans and caused disease. Bryce Falk’s research is focused on finding and identifying viruses in the Asian citrus psyllid, Diaphorina citri. These viruses, or genetically altered versions of them, could be potential tools to combat the Asian citrus psyllid to limit spread of the bacterium that causes huanglongbing (HLB) disease of citrus.
What is the technique?His lab collects RNA, rather than DNA, because most insect viruses have RNA as their genetic material and even those viruses with DNA genomes must make RNA during infection. The form of RNA from the virus is non-infectious and can be safely imported into the United States for analysis. RNA can also be used for sequencing of the genes in order to devise strategies to use PCR-based (polymerase chain reaction) techniques to find new viruses. So far, they have found 5 viruses in Asian citrus psyllid, three of which have potential to cause disease in the insect. They will use two strategies to study the three viruses separately and in combination to assess their effects on Asian citrus psyllid. The first strategy is to use the virus, as is, to attempt to disrupt Clas transmission. Reo virus DcRV is the only infectious virus found so far and it could play a role in blocking CLas in the insect. It is common in Hawaii but there is no HLB there. The second strategy is to modify certain viruses genetically to induce traits in the psyllid, making it less likely to transmit CLas. These viruses include a picorna-like virus, an associated C virus, and a denso virus. Currently they are putting these viruses into cell culture to understand their genetics and how they work. Similar efforts with viruses are underway for mosquitoes that spread diseases, such as malaria. Thus this project is timely and takes advantage of new opportunities to specifically target the Asian citrus psyllid. Understanding the psyllid genes that interact with the viruses could provide a clue as to how the psyllids resist viruses, which then could be used to our benefit by altering the genetics of the insect or the virus.
Who is working on the Project?
Bryce Falk, Professor of Plant Pathology at UC Davis, and his laboratory are surveying for the viruses, developing insect cell culture lines to grow the viruses, and determining if they could be used to reduce psyllid populations. This work is done within the UC Davis biosafety 3P Contained Research Facility (crf.ucdavis.edu) where they maintain two populations of the Asian citrus psyllid, one of which is virus-free and one of which has a virus which does not appear to be disease-causing. They maintain the viruses on cell cultures made up of other insects, such as fruit flies, moths or plant insects.
What are the challenges and opportunities?
Much research needs to be done to understand the genetic make-up of the viruses and how they act in the psyllid. If a virus naturally competes with the HLB bacterium in the psyllid or could be modified to compete with the bacterium, or in some other way reduce the psyllid’s ability to transmit the bacterium, then it could be used to slow the spread of HLB.
Funding source: This project is funded by the USDA-NIFA and Citrus Research and Development Foundation.