ASIAN CITRUS PSYLLID
UF/IFAS Photo by Michael Rogers
The Asian citrus psyllid is Florida’s most economically damaging insect, threatening the state’s $10.7 billion citrus industry. Estimated losses: $7.8 billion in total economic contribution from 2006/2007 through 2012/13 growing seasons, 162,000 acres of commercial citrus groves, 7,500 jobs.
Citrus fruit is Florida’s signature crop, and represents one of the state’s most valuable commodities. In recent decades, Florida has produced about 70 percent of the nation’s citrus crop, and the state’s citrus industry has generated about $10.7 billion in total economic impacts for Florida each year. Today, the industry is fighting for its very existence against a bacterial disease known as Huanglongbing or HLB (it’s also known by the colloquial name “citrus greening.”) The disease weakens and eventually kills citrus trees, and it is transmitted to healthy trees by an invasive insect known as the Asian citrus psyllid, Florida’s costliest agricultural pest.
Common Name: Asian citrus psyllid, also called the “ACP” by scientists
Scientific Name: Diaphorina citri
Good Bug or Bad Bug? Bad Bug
What It Is: The Asian citrus psyllid is a tiny, flying insect from the order Hemiptera, the true bugs. Within the Hemiptera order, it’s part of the family Psyllidae, which has had its name changed recently to Liviidae. Under either name, the family includes many plant-feeding insects that are collectively known as psyllids or jumping plant lice. Like most psyllids, the Asian citrus psyllid is very host-specific, and feeds almost exclusively on citrus trees, though it can make do with other tree species in the family Rutaceae.
What It Does: The Asian citrus psyllid transmits the bacterium that causes HLB. The insect must first acquire the bacterium from an infected citrus tree, via its feeding behavior. It uses needle-like mouthparts to pierce tender tissue in new citrus shoots and consume fluids from tissue called the phloem, which serves as the tree’s circulatory system. If the tree is infected and individual HLB bacteria are circulating in the phloem, a feeding psyllid is likely to consume some of the bacteria. If the bacteria can survive and reproduce within the psyllid’s internal environment, the psyllid becomes capable of transmitting the bacterium – what’s known as a “vector” in entomological terms. (See our Bug Word of the Day feature during Bug Week May 21-27 for more on the term vector.)
If the psyllid already carries the bacterium that causes HLB, then it may inadvertently transmit the bacterium to the uninfected citrus tree as it feeds. Once an infection is established, the bacterium multiplies and moves through the tree via the phloem. The disease we know as HLB is simply a manifestation of the bacterium’s effects, as it damages roots and starves the tree of nutrients. The tree’s foliage yellows, unripe fruit may drop to the ground prematurely, and the quality and quantity of mature fruit gradually declines. Infected trees eventually die, and there is no cure for HLB.
Who Is Affected: Commercial citrus growers and dooryard citrus growers throughout Florida. The USDA citrus production forecast for April 12, 2016 indicates that the state’s 2015/2016 orange crop will be 76.0 million boxes, less than one-third of the amount harvested in the 2003/04 season, 242 million boxes. Similarly, the 2015/2016 grapefruit harvest forecast calls for 10.7 million boxes, barely one-fourth the amount harvested in the 2003/2004 season, 40.9 million boxes. In the U.S., HLB has also been detected in Georgia, Louisiana, South Carolina, Texas and in several residential trees in California. HLB also affects other citrus-producing nations such as China and Brazil.
Where It’s Found in Florida: HLB was first reported in Florida in September 2005, in Miami-Dade County. Today, the disease is present in every Florida county with significant commercial citrus production, and is believed to infect 80 percent of Florida’s citrus trees and 90 percent of the state’s citrus acreage.
How It’s Currently Addressed: Florida citrus growers have taken myriad steps to protect their operations from HLB. Some of the most common have included the use of management practices designed support overall tree health or enable trees to survive HLB infection, insecticide applications to reduce populations of the Asian citrus psyllid, bactericide applications to fight the bacterium that causes HLB, prompt removal and destruction of infected trees, and generation of research funding through grower-approved “box taxes” that channel a small amount of growers’ revenues into a fund used to support citrus research and Extension efforts.
Native to Florida? No. The Asian citrus psyllid is native to Southwestern Asia.
Big Money Associates: The bacterium Candidatus Liberibacter asiaticus. The term Candidatus means that scientists have not yet cultured the bacterium under laboratory conditions. In turn, this means scientists have not been able to conduct an important experiment, in which they take a pure culture of the bacterium and inoculate healthy citrus trees with it, then wait to see if the trees develop HLB. Without this experiment, scientists cannot be 100 percent certain that Candidatus Liberibacter asiaticus causes HLB. However, there is very little doubt that the bacterium is responsible – molecular genetic analysis by UF/IFAS researchers has virtually ruled out the possibility that any other pathogen is involved.
Interesting Fact: Ants feed on the sugar-rich waste product excreted by the Asian citrus psyllid, and the presence of ants can discourage natural enemies from preying on psyllids in citrus groves. This factor can disrupt biological control programs that use natural enemies against the pest.
Estimated Losses Per Year: In Florida, from the 2006/2007 citrus growing season through the 2012/2013 growing season, HLB caused the state’s economy to lose approximately $7.8 billion in total output from the citrus industry; the disease also eliminated 162,200 acres of commercial citrus groves and 7,513 jobs. (These losses are associated strictly with oranges used for orange-juice production, which represent about 95 percent of the state’s orange crop; the figures do not include losses in other sectors of the citrus industry, such as fresh-market oranges and other citrus varieties such as grapefruit.)
Other Costs: Since 2008, more than $176 million has been spent on research to fight HLB, according to the Florida Department of Citrus; about $71 million of that figure came from grower-funded “box taxes.”
What Is UF/IFAS Doing About It? At this point, almost 11 years after the disease was first confirmed in Florida, UF/IFAS has probably devoted more resources to HLB than to any other crop disease in the state’s history. Much of the work has taken place at the UF/IFAS Citrus Research and Education Center in Lake Alfred, the world’s largest facility dedicated to the scientific study of citrus production.
Current HLB-related initiatives at UF/IFAS address everything from improved scouting and field-testing for identifying infected trees, to better ways of locating and attracting the Asian citrus psyllid for monitoring and control efforts, to improved insecticide-application protocols, to new management practices that support overall tree health, to citrus breeding efforts aimed at developing varieties with enhanced disease resistance.
Strong funding support has assisted these efforts. In February 2015, the U.S. Department of Agriculture announced $23 million in additional funding from the 2014 U.S. Farm Bill’s Citrus Disease Research and Extension program. As a result, four projects led by UF/IFAS personnel received funding that ranged from $2.1 million to $4.6 million. The projects include investigations on systemic antimicrobial compounds to support tree health, efforts to breed HLB-resistant trees, and a project to scale up the technology needed to apply steam treatments to individual trees, slowing disease progression.
In February 2016, USDA announced $20.1 million in funding for HLB research, including a UF/IFAS-led team that will receive $3.99 million for a new effort to culture the Candidatus Liberibacter asiaticus bacterium under laboratory conditions.
In April 2016, USDA announced that it would soon allocate another $22 million in funding for HLB research.
Since 2007, UF/IFAS has helped organize the Citrus Health Management Areas (CHMA) program, an Extension effort to improve the effectiveness of psyllid management. This voluntary effort encourages citrus growers in specific geographic areas to coordinate their insecticide applications, so that all of their groves are treated on the same days. This strategy makes it less likely that psyllids will manage to escape insecticide exposure by flying to nearby, untreated citrus acreage. Currently, there are 55 CMHA groups, representing about 486,000 acres of commercial citrus statewide.
What Can YOU Do About It? If you have any citrus trees on your property, even for ornamental purposes, it’s a good idea to become familiar with HLB and its symptoms. If a seemingly healthy tree begins an unexpected decline, it should be tested for HLB and destroyed if infected. UF/IFAS citrus breeders are working on developing HLB-resistant citrus varieties, which should be available one day as an option for homeowners who wish to replace dooryard citrus trees killed by HLB.
Also, PLEASE do not transport fresh citrus fruit or citrus plants from one state to another – it’s possible that you’ll accidentally introduce HLB to an area where it is not currently established.
Read more about the Asian citrus psyllid in this “Featured Creatures” document produced by the UF/IFAS Entomology and Nematology Department. http://entnemdept.ufl.edu/creatures/citrus/acpsyllid.htm
Read more about the impact of HLB on Florida citrus production in this document from the EDIS online Extension library. https://edis.ifas.ufl.edu/fe983
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