Although flies are known for being buzzing nuisances, they play a vital role as one of the most prolific pollinators on Earth. A new study led by scientists at Pennsylvania State University in the United States shows that flies are increasingly at risk as global temperatures rise.
In a recent study published in the Journal of Apiology, an international team of researchers examined the heat tolerance of several species of bees and flies in tropical and subtropical America. The findings suggest that rising temperatures pose a greater threat to flies than to bees, because bees can tolerate higher temperatures and have a wider range of habitats than flies.
"Bees and flies are essential for plant pollination, both in the wild and in agriculture," said Margarita López-Uribe, one of the paper's authors and an associate professor of entomology at Penn State. "However, these important insects are in decline due to the growing threats of habitat loss, pesticides, disease and climate change."
López-Uribe explained that flies play a vital role as pollinators, second only to bees in terms of the number of crops and habitats they pollinate. Flies are particularly important to the overall health and diversity of wild ecosystems because they facilitate the reproduction of countless plant species, which in turn provide food and habitat for other organisms. Flies are also making an increasing contribution to agriculture. For example, flies are the main pollinators of the cocoa tree, which produces the fruit that is used to make chocolate.
In 2020, an analysis of global crops found that the 105 most widely grown crops that benefit from pollinators have a combined economic value of more than $800 billion, including many of the world's most popular and nutritious fruit, vegetable and nut commodities. The study also found that flies, specifically hoverflies and blowflies, continue to be the top pollinators after bees.
"It's time to give flies more recognition as pollinators," López Uribe said. "Flies have an important role, but they don't get enough attention, and they are just as vulnerable as bees."
López Uribe explained that insects are particularly vulnerable to rising temperatures because of their limited ability to regulate their body temperature. To understand how different pollinator species respond to rising global temperatures, researchers studied the "critical thermal maximum" (CTMax) of bees and flies, which is the highest temperature they can withstand before losing the ability to move.
Researchers found that bees can tolerate higher temperatures than flies. On average, the CTMax of bees is 2.3 degrees Celsius higher than that of flies. They also found that time affects the bees' heat tolerance. Bees foraging in cool mornings had higher CTMax than bees foraging in warm afternoons. The study also showed that geography plays an important role in heat tolerance.
International students from Penn State and other universities participating in the project conducted research in their respective countries. From this, López-Uribe said, they were able to collect data on bee and fly species across the Americas.
“We sent all of our research equipment to students in the United States and South America,” López-Uribe said. “The students collected data at home, using their kitchens to understand the thermal ecology that these insects can withstand.”
The team found that flies and bees from high-altitude tropical regions such as Cajicá, Colombia, had lower CTMax values than their counterparts from subtropical regions such as California and Texas in the United States. This suggests that insects in cooler, higher-altitude environments may be more susceptible to small increases in temperature.
"Flies are the primary pollinators in alpine and subarctic environments," said López Uribe. "This study shows that as the climate warms, some areas of the planet may lose key pollinators, which could be catastrophic for these ecosystems."
Related paper information: https://doi.org/10.17161/jom.vi122.22505