Detections of invasive fruit flies are sharply on the rise in the U.S. this year, triggering a multimillion dollar response from federal, state, and local government agencies aimed at protecting our agricultural resources. One entomologist argues for renewed dedication to sensible biosecurity measures—including strategies that harness travelers’ feelings. Shown here is an Oriental fruit fly (Bactrocera dorsalis) on lychee fruit. (Photo by Gary Steck, Florida Department of Agriculture and Consumer Services)

By Jiri Hulcr, Ph.D.

Jiri Hulcr, Ph.D.

Do you remember that blue piece of paper that used to be handed out on flights to the U.S.? It asked passengers to declare whether they were bringing any fruits, meat, or other fresh foods with them and whether they had recently been on a farm. The purpose was to help customs officials intercept goods that might transport pests and pathogens—including insects—into the U.S.

Until recently, the U.S. Department of Homeland Security required passengers to declare agriculture and food-related items on a Customs and Border Protection (CBP) Form 6059, Declaration of Importation. Here is the crux of the matter: The requirement to declare stinky cheese from France or guava from Thailand is still in effect, by law. The CBP has all the rules nicely outlined on the website. The problem is that it ends there. At most airports, the focus has now shifted to the surveillance for prohibited items by the CBP officers themselves. Perhaps you have seen the occasional sniffer dog or were asked about food in the immigration interview. Most of us haven’t. The agency dropped the requirement that each passenger actively checks the box. By discontinuing the simple act of participation, the agency lost an opportunity to get travelers thinking about the issue of biosecurity.

In other words, the attempt to make arrivals more effective has led to the loss of behavioral intervention and education of millions of travelers. Unfortunately, the “simplified egress” is correlated with a recent sharp increase in the establishment of food related pests, such as fruit flies.

When bugs or fungi from other continents get into the United States, they sometimes cause problems in our agriculture and natural ecosystems—and that’s an understatement. In reality, the avalanche of invasive pests and diseases is one of the largest environmental catastrophes unfolding in front of our eyes, second only to climate change. The impact from this mixing of organisms is in trillions of dollars globally and over $2 billion just to the U.S. in direct annual damage. Lots of the damage is incalculable, beyond money. How much value are we losing by having entire tree species wiped out from our landscapes by invasive pests and diseases? How do we calculate the impact of this foreign pest pressure when it prevents farmers from growing fruit without insecticides? Or when they cannot farm at all, and lifestyles and industries are lost? Invasive species are becoming a national biosecurity crisis.

So, agriculture and trees are important, and invasive pests are now slamming them beyond any historical record. What does that have to do with a form on an airplane?

Exotic Fruit Flies

The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) exists to protect the health and value of American agriculture and natural resources. And it is a busy agency. This year, its number one priority has unexpectedly become exotic fruit flies. I don’t mean the tiny flies that hover around the fruit basket in your kitchen; those are technically called vinegar flies and are harmless. (They are also an important model species in genetic laboratories.) I mean the true fruit flies (for the entomology nerds: family Tephritidae), which are larger than a house fly and brightly colorful. You may have heard of the infamous Med fly or the Oriental fruit fly; there are dozens of other species. The females lay eggs on unripe fruit. The maggots develop inside the fruit before anyone even sees them, and then they ruin it for human consumption.

The federal USDA and its state counterparts in fruit-heavy states run surveillance programs for these fruit flies, which include weekly checking of tens of thousands of special traps. The program costs millions of dollars, but this prevention is a fraction of what it would cost if we were to let the exotic fruit flies establish. Should Florida, California or Texas become infested with one of these tropical fruit fly species, the damage to fruit industries could go into hundreds of millions of dollars. In addition, it would be essentially impossible to avoid spraying fruit with insecticides, or it would require that each individual peach or pepper is protected with a wrapper or that fruit and vegetable fields be put under quarantine, or some other interventions that would put many growers out of business. As Trevor Smith, director of Florida Department of Agriculture’s Division of Plant Industries, told me, “The growers are nervous.”

In regular years, the agencies detect a couple of exotic fruit flies, and each triggers an Incident Command System response. (Seriously, it is borrowed from the military, because it is that important.) Government representatives jump to work with municipalities and farmers to eradicate each invasive fly population, using methods ranging from insecticides to striping fruit from trees to the sterile insect technique (flooding the landscape with millions of fly males that were irradiated into sterility, which crashes the population).

However, this spring, over a hundred separate fruit fly invasions were detected just in California. This has never happened before. This is an order of magnitude greater risk, which has required an immediate focus of the federal and state agencies (APHIS 2024), millions of dollars, and the deployment of hundreds of specialists. The APHIS Invasive Fruit Fly Survey in California alone will cost $4,500,000 this year. This is when the issue of invasive species becomes about food security.

Where Are They Coming From?

What is unique about this year’s situation is that most of the detections were in urban backyards. These flies are not arriving in shipping containers to ports or to packing warehouses. An analysis by the Florida Department of Agriculture suggests that these flies are arriving on fruit that travelers bring with them from overseas. Did you return from Southeast Asia with fun spicy peppers but noticed that one is a little shriveled up? Did your grandma from the Caribbean bring a mango for the kids, but maybe you found maggots in it? Did you throw it in your yard compost? Suddenly we could have a multimillion-dollar eradication program.

But it’s not just about fruit flies. Florida is known for beaches, hurricanes, and citrus! But did you notice that your bottle of orange juice increasingly indicates other countries as the source? Around 2005, a new disease called citrus greening showed up in Florida—caused by a bacterium vectored by a small leafhopper—and started killing citrus trees. In less than two decades, the entire industry is in shambles. Another famous fruit from Florida, the avocado, is similarly struggling with a new disease. This one is called laurel wilt and is caused by an exotic fungus vectored by a tiny ambrosia beetle. A single dose of it kills an entire mature avocado tree in a few weeks. Now, imagine what happens if that disease gets into California, which has 10 times greater avocado production than Florida. Or if someone accidentally brings it to Mexico, which produces 100 times more! The end of guacamole would be the smallest problem. A bigger issue would be farmer poverty, migration, and crime. There is a reason the freshly published USDA National Farm Security Action Plan calls these pest invasions a national security issue.

This avocado grove in south Florida was devastated by laurel wilt, a new disease caused by an invasive fungus, Harringtonia lauricola, brought to the U.S. by a beetle native to Asia, Xyleborus glabratus. (Photo courtesy of Jiri Hulcr, Ph.D.)

There are now so many new plant pests and diseases arriving—as many as three per month just in my state of Florida—that playing a “whack-a-mole” trying to eradicate every one of them is futile. It would be much more effective to prevent their arrival. And that is why in the early 2000s, USDA APHIS teamed up with the Department of Homeland Security, specifically CBP, to develop programs to secure airports and other kinds of ports so that unwanted bugs don’t get through.

How many prohibited items do passengers bring to the U.S. every year from overseas? Nobody knows for sure, but let’s do some quick estimation: The United States has the world’s highest yearly rate of pest interceptions at airports, both total and per traveler. Agricultural or food items are found with approximately 3% of airline passengers. In 2022, 102 million passengers arrived in the U.S. on international flights. Three percent of those passengers is approximately 3,060,000. Not all of them carry pests, but many do. This a rain of pests. We need an umbrella.

Harness People’s Feelings

An immediate step to prevent further escalation of pest introductions via passenger traffic would be renewed dedication to sensible biosecurity measures within the Department of Homeland Security.

However, such measures do not necessarily mean more infrastructure or large expenses. Instead, what is needed is a simple tool to change passengers’ attitude. An example can be a return to the requirement to fill out a blue paper form. The psychological and educational impact, scaled up, would outsize the modest investment. We know that a voluntary pledge to abide by certain rules can scale up to societal change because of the emotional discrepancy between incorrect action and the societal standard. Some people will lie, and will not be caught, but the interception rate is not relevant. What is important right now is to make millions of people feel bad about bringing fruit across the border and feel good about their contribution to our shared responsibility.

Participatory campaigns have been effective in many public behavior changes related to environmental issues, particularly when positive education is combined with an element of the fear of being caught. The existing “Don’t Pack a Pest” campaign could be intensified at ports of entry to complement paper forms. Perhaps we don’t even know what the most strategic and cost-effective strategy is to bring the nation on board with biosecurity. But the billion-dollar damage imparted on the U.S. economy by invasive species more than justifies greater focus on this pathway.

Jiri Hulcr, Ph.D., is a professor with the School of Forest, Fisheries, and Geomatic Sciences and the Department of Entomology and Nematology at the University of Florida and principal investigator of the UF Forest Entomology Lab. Email: [email protected].