Rome — In the United States, it is a wood-borer beetle that arrived in packaging and which has indirectly caused an estimated 21,000 premature human deaths. In South Korea, it is a worm that forced the government to cut down 10 million pine trees.
And in Africa, it is a maize-munching pest from the Americas that has infested millions of hectares of crops, and threatens the food supply and income of more than 300 million people.
What do they have in common? All three crossed continents to cause havoc on plants.
Although such challenges have been with humankind since the advent of farming, experts warned this week that climate change and biodiversity loss could accelerate and expand their spread.
"You are going to have extreme weather events that can spread these pests more readily," Geoffrey Donovan, an economist with the United States department of agriculture (USDA), told the Thomson Reuters Foundation.
"It cannot be a good thing at all," said Donovan, who has conducted studies on links between trees and human health.
Viliami Kami, chief entomologist at Tonga's agriculture ministry, agreed that higher temperatures, longer and more severe droughts, and stronger and more frequent cyclones could lead to pest and disease outbreaks.
Pests already cause losses of around $220 billion a year, or around 10-16 percent of harvests, the United Nations' Food and Agriculture Organization (FAO) said at a conference this week.
At the same time, trade in agricultural products is vast: it is worth $1.1 trillion annually, the FAO said, of which food accounts for 80 percent.
But unless this process is carefully managed, it brings increased risks of pests and diseases taking hold in new countries, the FAO warned.
That can happen with the products themselves, but there are risks too with the packaging in which they are shipped: most is made of wood, said Lois Ransom, chair of the Commission on Phytosanitary Measures (CPM), which organised the conference.
"If you don't look after plant health, we would have massive challenges around achieving food security, protecting the environment and facilitating safe trade," Ransom told the Thomson Reuters Foundation on the sidelines of the conference.
CPM is the governing body for the International Plant Protection Convention (IPPC), an international treaty established in 1952 to prevent pests and diseases spreading across international borders via trade.
This week, the CPM adopted new and revised standards for countries to use to prevent pests from jumping borders, including the use of gas insecticide and heating technologies to treat wooden packing materials, killing pests deep inside.
Consequences of a failure to protect plants could go beyond hunger and jobs, and the impact can last generations, said Ransom, an assistant secretary at Australia's department of agriculture and water resources.
She pointed to how Ireland's 19th century potato famine killed an estimated million people and saw at least another million emigrate.
"Imagine if Xylella in olives get into the Middle East, where olives are grown in small communities, supporting families," she said, referring to a vector-borne pest that can attack over 350 plant species, and which has already reached Italy and France.
"If they can no longer grow the olives, then people may have to move. It's an area of social unrest anyway and ... you're just compounding a really difficult situation," Ransom added.
PREVENTION BETTER THAN CURE
The USDA economist Donovan urged experts and officials from 140 countries attending the conference to see trees as a public health infrastructure, "a fundamental part of human well-being".
In 2013, Donovan conducted a study that found U.S. counties infested with the emerald ash borer beetle had higher levels of human deaths linked to cardiovascular and lower-respiratory diseases.
"And this increases as the infestation progresses ... the more trees die, the more people die," he told the conference.
The emerald ash borer, an invasive beetle native to Asia, has killed hundreds of millions of ash trees in 31 states since it was confirmed in Detroit, Michigan, in 2002, Donovan added.
His study estimated more than 21,000 people had died in 15 states because there were fewer trees providing health benefits.
In South Korea, where pine trees are cultural, historical and ecological cornerstones, containing the pine wood nematode has cost over $600 million in 20 years, said Kyu-Ock Yim, senior researcher at the country's animal and plant quarantine agency.
"There was the loss of forest and crop but there are so many indirect impacts too - the ecology, the social impact and the environment which are not easily estimated," said Yim.
Preventing the arrival of such pests and diseases - in this case, originally from North America - "is the most cheap and effective way", she added.
Yet this could be a challenge, with e-commerce on seeds and plants growing, and tourism a globally important industry.
"The really problematic situations are where you get that continental shift - pests go from one continent to another where you've got hosts growing right through that continent," said Ransom, the CPM chair.
"Once they're inside ... you can't do anything. You just got to try and mitigate the impact," she added.
Ransom also has advice for tourists eager to bring food from home or souvenirs from their travels in different continents.
"Do not pack food. Do not take fresh fruit. Clean your camping equipment. It's about an awareness that (what you bring) can have an impact forever."
- Reporting by Thin Lei Win @thinink, Editing by Robert Carmichael