Stopping the virus's spread is an uphill battle
The future of your favourite chocolate is uncertain due to a devastating virus rapidly wiping out cacao trees in West Africa. These trees produce the cocoa beans essential for making chocolate. Shockingly, half of the world's chocolate comes from cacao trees in Ghana and Cote d'Ivoire.
A new study published in PLoS ONE reveals a frightening truth: Ghanaian cacao harvests are experiencing massive losses (15-50%) due to the spread of Cacao Swollen Shoot Virus Disease (CSSVD).
Tiny insects called mealybugs are the culprits, transmitting the virus as they feed on infected trees. This virus causes a range of nasty symptoms in healthy trees, including swollen shoots, discoloured leaves, and distorted growth.
Infected trees see their yields plummet within the first year and typically die within a few years. Sadly, over 250 million trees have already succumbed to this disease.
"This virus is a real threat to the global supply of chocolate," study co-author Benito Chen-Charpentier, a professor of mathematics at The University of Texas at Arlington, said in a statement.
Stopping the virus's spread is an uphill battle because the mealybug carriers are very difficult to eradicate.
"Pesticides don't work well against mealybugs, leaving farmers to try to prevent the spread of the disease by cutting out infected trees and breeding resistant trees. But despite these efforts, Ghana has lost more than 254 million cacao trees in recent years," Chen-Charpentier said.
Vaccinating the trees seems like a viable option, but it has limitations. The high cost of the vaccine creates a barrier for many farmers, and even vaccinated trees produce less cocoa.
The researchers offer a potential solution in the new paper: strategically spacing the trees. Their models show that planting cacao trees at specific distances from each other could disrupt the mealybugs' travel routes, hindering the spread of the virus.
"Mealybugs have several ways of movement, including moving from canopy to canopy, being carried by ants or blown by the wind," Chen-Charpentier said. "What we needed to do was create a model for cacao growers so they could know how far away they could safely plant vaccinated trees from unvaccinated trees to prevent the spread of the virus while keeping costs manageable for these small farmers."
In the paper, the researchers describe two models that surround unvaccinated trees with vaccinated trees, creating a sort of herd immunity in the plantation.
"While still experimental, these models are exciting because they would help farmers protect their crops while helping them achieve a better harvest," Chen-Charpentier said. "This is good for the farmers' bottom line, as well as our global addiction to chocolate."