New Research Reveals Flies Among the Most At-Risk Pollinators in a Warming World

In a study recently published in the Journal of Melittology, a global group of researchers examined heat tolerance among various species of bees and flies in tropical and subtropical areas of the Americas. Their results indicate that increasing temperatures pose a more significant threat to flies than to bees, given that bees can withstand much higher temperatures than flies and possess a wider range of habitats.

“Bees and flies are crucial for pollinating vegetation, both in natural ecosystems and in agriculture,” stated Margarita López-Uribe, the Lorenzo Langstroth Early Career Associate Professor of Entomology at Penn State, extension specialist in pollinator health and lead author of the research. “Nonetheless, these essential insects are in decline due to habitat destruction, pesticides, diseases, and the mounting risks associated with climate change.”

Flies have a vital function as pollinators, coming second only to bees regarding the volume of plants and environments they pollinate, López-Uribe clarified. Flies are particularly significant for the overall health and diversity of wild ecosystems, as they enable reproduction for numerous plant species, which in turn furnish food and habitat for other creatures. Moreover, flies are increasingly aiding agriculture. For instance, flies serve as the primary pollinators for cocoa trees that yield the fruits used in chocolate production.

A 2020 assessment of global crops revealed that the 105 most commonly cultivated crops benefiting from pollinators have a gross economic value exceeding $800 billion and include many of the most favored and nutritious fruits, vegetables, and nut commodities consumed globally. The study also demonstrated that flies, particularly hoverflies and blowflies, consistently ranked just behind bees as major pollinators.

“It’s time we acknowledged the importance of flies as pollinators,” remarked López-Uribe. “Flies play a significant role, yet they do not receive enough recognition — they are at risk in the same ways that bees are.”

Insects are particularly vulnerable to rising temperatures since they have a limited ability to regulate their body heat, López-Uribe noted. To comprehend how different pollinator species might adapt to increasing global temperatures, the researchers investigated the bees and flies’ “critical thermal maximum,” or CTMax — the highest temperature they can endure before losing the ability to move.

The research team discovered that bees can endure considerably higher temperatures compared to flies. On average, the CTMax for bees was 2.3 degrees Celsius greater than that of flies. They also noted that the time of day influenced the heat tolerance of bees. Bees foraging in the cooler morning hours exhibited a higher CTMax than those active during the warmer afternoon. The study further revealed that geography has a bearing on heat tolerance.

The team gathered data throughout the lockdowns of the COVID-19 pandemic, which meant that international students involved in the project, from Penn State and various other universities, conducted research in their home countries. López-Uribe explained that the challenge ended up being advantageous, as students were able to collect data on bee and fly species across the Americas.

“We dispatched all the necessary equipment for the study to students across the U.S. and South America,” López-Uribe stated. “These students collected data in their homes, utilizing their kitchens to explore the thermal ecology that these insects could withstand. We effectively created an international research experience without being able to travel worldwide.”

The research team found that flies and bees from elevated tropical areas such as Cajicá, Colombia, had lower CTMax values than their counterparts in subtropical regions like California and Texas. This indicates that insects in cooler, high-altitude regions may be more susceptible to even minor temperature increases.

“In alpine and subarctic regions, flies serve as the key pollinator,” López-Uribe asserted. “This study reveals that we may lose our primary pollinator in entire areas as the climate warms, which could lead to disastrous effects for those ecosystems.”

Other authors from Penn State on the article include Ruben Martín-Rojas, a graduate student in the entomology department; José Fuentes, a professor of meteorology; and Luis Duque, an assistant research professor in storage root physiology. Additional contributors to the paper are Maren Appert from San Diego State University, Alonso Delgado from the University of Texas at El Paso, Abigail Jimenez from California State University, Victor Ramos from Pontificia Universidad Católica del Perú, Andrés F. Herrera-Motta, Diego Riaño-Jimenez, and José R. Cure from Universidad Militar Nueva Granada, Bogotá, Colombia, and Victor Gonzalez from the University of Kansas.

The research was funded by a grant from the U.S. National Science Foundation, which backed an International Research Experience for Students program.