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GM Mosquitoes, Citrus and Antibiotics: Recipe for Disaster?

Citrus fruits are not native to the U.S., but they are now an integral part of Florida's agricultural growth and state identity. Citrus trees came with Europeans in the 1500s and quickly began growing in Florida. In return for serving during the Seminole War several hundred years later, John Eaton was given land under the government's plan. This was the birth of the citrus industry in Florida.1

Eaton lived in what is now Orange County, where his experiments with grafting helped establish the crop. Farmers took them north into the Carolinas and Georgia to reduce shipping costs after the fruits were harvested,2 but a freeze in 1835 destroyed all crops growing in those states.3 Farmers recognized the need for warmer winters and began moving the industry back to Florida.

In the early 1900s, the middle of the state was home to almost all of the entire citrus crops flourishing at that time. Another freeze hit central Florida in 1895, and, in one night, the entire industry was decimated. Few of the old groves were re-established, so the industry moved even farther south.4

Today, citrus is a $9 billion industry. Florida’s subtropical climate and its vast areas with sandy soil present ideal conditions for growing these brilliant, fragrant trees.

What Is Citrus Greening?

Citrus huanglongbing (HLB), also known as citrus greening, is a destructive disease that was first thought to be caused by a virus. It's now known that the Asian citrus psyllid infects the trees with bacteria while it munches away on the leaves, twigs and stems. This hurts the tree’s ability to absorb nutrients.5 Once this happens, the tree produces sour-tasting fruit, eventually reducing production and dying.

To date, there is no cure for the disease and rapidly removing the trees is crucial to reducing its spread.6 The bacteria are able to infect most citrus trees, and even some relatives.

Since the disease was discovered in 2005, the number of acres dedicated to citrus growth has declined significantly. The disease has also been found throughout the southeastern U.S., the Caribbean, Asia and the Middle East.7

In the past 15 years, the infection spread rapidly across Florida and resulted in a 72.2% reduction in the production of oranges and a 20.5% reduction in the fresh fruit market overall.8 Even more disturbing than these statistics is the lack of scientific evidence about the bacteria.

Farmers are spraying antibiotics to protect the orchards, yet the bacteria have still not been successfully grown in the lab.9 The disease is associated with the gram-negative bacterium Candidatus Liberibacter. In the early stages, farmers find it difficult to make a diagnosis.10

Scientists are unsure how long a tree may be infected before symptoms begin to appear. Initially, farmers may find some thinning in the top branches with twig dieback and discolored leaves. An imbalance in sugar transport and accumulation also affects the nutritional content of the fruit, which becomes asymmetric and poorly colored as the disease progresses.

EPA Approves Antibiotics to Treat Citrus Greening

Some estimate that 90% of Florida’s citrus groves are infected with HLB.11 Nearly two-thirds of the factories are closed, and packing operations have been cut from nearly 80 to 26 in the state.

The loss of groves and production could mean death to the state's citrus agriculture that produces 80% of the orange juice consumed in the U.S. In the face of this devastating loss, the U.S. Environmental Protection Agency expanded the use of two broad-spectrum antibiotics in 2016, 2017 and 2018 that are medically important in treating human illnesses. These are oxytetracycline and streptomycin.12

It was hoped that application to citrus groves in Florida and California would prevent HLB. Yet, without adequate research showing the antibiotics could be effective and would not lead to further antimicrobial resistance, the decision reads as though the agency is throwing the kitchen sink at the problem and hoping it works.

In a press release following the announcement of emergency use of oxytetracycline in 2018, the Center for Biological Diversity pointed out three vital issues the EPA was failing to consider in the approval, writing:13

“In setting the tolerance level the EPA failed to analyze how the antibiotic could affect gut bacteria in humans that play a critical role in digestion, metabolism and immune system health.

The agency also failed to assess how fruit trees treated with the antibiotic year after year could affect the development of human pathogens resistant to the tetracycline class of antibiotics. And the EPA failed to consider the potential harm increased use of the antibiotic could cause to the nation’s most endangered wildlife.”

In late 2019, lawmakers expressed concerns that an overabundance of these antibiotics in the environment would only exacerbate antibiotic resistance.14 In a letter signed by seven lawmakers, the EPA was urged not to authorize the expanded use of streptomycin on farms in Florida and California after oxytetracycline had been approved in 2018.

Spraying has not solved the problem. The expanded use proposed in late 2019 allowed growers to use 650,000 pounds of streptomycin and 338,000 pounds of oxytetracycline every year. The University of Minnesota Center for Infectious Disease Research and Policy published part of the letter sent to the EPA, which said:15

"Antibiotics are life-saving medicines and, except in extraordinary circumstances, should only be used to treat specific illnesses in people and animals. EPA's assessments appear to ignore scientific evidence, violate the principle of judicious antibiotic use, and could create unnecessary harm to human health by authorizing an unprecedented amount of medically important antibiotics to be used for plant agriculture."