While often viewed as bothersome creatures, flies actually play a vital part as some of the most effective pollinators on our planet. Recent research led by scientists at Penn State indicates that these insects are increasingly threatened by the rise in global temperatures.
A recent study published in the Journal of Melittology examined the heat resilience of several bee and fly species found in tropical and subtropical areas of the Americas. The results suggest that flies are at greater risk from escalating temperatures compared to bees, who can endure much hotter conditions and have a broader range of habitats.
“Both bees and flies are crucial for pollinating various plants, whether in natural settings or agricultural fields,” stated Margarita López-Uribe, Early Career Associate Professor of Entomology at Penn State and the lead author of the study. “Regrettably, these essential insects are facing declines due to factors like habitat destruction, pesticide use, diseases, and the looming threat of climate change.”
According to López-Uribe, flies are indispensable as pollinators, ranking just behind bees in the amount of crops and habitats they help pollinate. They are particularly significant in maintaining the health and diversity of wild ecosystems, as they enable the reproduction of numerous plant species, which subsequently provide nourishment and living spaces for other creatures. Moreover, flies are becoming increasingly important in agriculture. For instance, they are the main pollinators for cocoa trees that yield the fruits used to produce chocolate.
A 2020 analysis of global crops revealed that 105 of the most widely cultivated crops benefiting from pollination hold a total gross economic value exceeding $800 billion, and these include many of the most sought-after and nutritious fruits, vegetables, and nuts consumed globally. Additionally, the study found that flies, particularly hoverflies and blowflies, often come in just after bees as top pollinators.
“It’s time to acknowledge flies more for their role in pollination,” remarked López-Uribe. “These insects are crucial, yet they don’t receive the recognition they deserve, and they are vulnerable to the same threats as bees.”
Insects, including flies, are especially sensitive to rising temperatures as they have a limited capacity to regulate their body heat, López-Uribe noted. To investigate how different pollinator species may adapt to increasing global temperatures, the researchers measured the “critical thermal maximum” (CTMax) of the bees and flies, which indicates the highest temperature they can endure before becoming unable to move.
Findings indicated that bees can handle much higher temperatures compared to flies, with bees having an average CTMax that is 2.3 degrees Celsius greater than that of flies. The study also highlighted that the time of day affects bees’ heat tolerance; those foraging in cooler morning hours exhibited higher CTMax compared to those active in the warmer afternoons. Geographic location also appeared to influence heat tolerance.
The research team gathered data during the COVID-19 lockdowns, allowing international students from Penn State and other universities to conduct research from their home countries. López-Uribe shared that this challenge turned out to be beneficial, as it enabled students to collect data on bee and fly species across the Americas.
“We sent all the necessary equipment to students throughout the U.S. and South America,” López-Uribe explained. “They were able to gather data from home, often using their kitchens to study the thermal ecology of these insects. This allowed us to facilitate an international research experience without the necessity of traveling abroad.”
The team discovered that flies and bees from high-altitude tropical regions, such as Cajicá, Colombia, exhibited lower CTMax values compared to their counterparts in warmer subtropical areas like California and Texas. This finding implies that insects in cooler mountain environments could be more susceptible to even minor temperature increases.
“In alpine and subarctic regions, flies serve as the primary pollinators,” López-Uribe remarked. “Our study highlights that vast areas could lose their primary pollinators as temperatures rise, which could have dire consequences for those ecosystems.”
Others from Penn State contributing to the paper include Ruben MartÃn-Rojas, a graduate student in entomology; José Fuentes, a meteorology professor; and Luis Duque, an assistant research professor specializing in storage root physiology. Co-authors from other institutions include Maren Appert of San Diego State University, Alonso Delgado of the University of Texas at El Paso, Abigail Jimenez of California State University, Victor Ramos from Pontificia Universidad Católica del Perú, and several researchers from Universidad Militar Nueva Granada in Bogotá, Colombia as well as Victor Gonzalez from the University of Kansas.
This research was funded by a grant from the U.S. National Science Foundation, which supports an International Research Experience for Students program.
