An adult frosted alfin butterfly
GAINESVILLE, Fla. — Deciding how often and when to use prescribed fire can be tricky, especially when managing for rare butterflies, University of Florida scientists say.
That realization stems from a UF Institute of Food and Agricultural study in which researchers experimented with pupae — insects in their immature form between larvae and adults — of butterflies known to frequent fire-prone habitats of Florida.
Prescribed burns and wildfires can damage animals and plants in their paths. But they can also promote species and create habitat, maintaining the ecological balance of the forest and the region’s most frequent natural disturbance over the long term. Immature butterflies may die immediately following controlled burns, but populations can recover over time, with the amount of time depending on the species.
Scientists are concerned that butterflies with small, isolated populations may be in severe peril if their habitats are burned too frequently and in large blocks at a time, which can mean that butterfly refugia – unburned areas that provide refuge — are limited.
In the UF/IFAS study, scientists wanted to know how and why some butterflies survive wildfires and prescribed burns, particularly where the insect feeds and lays eggs on fire-adapted plants.
Prescribed fire for butterfly research
To date, most studies on the impact of fires on insects have been done in the Midwest, said Jaret Daniels, a UF/IFAS associate professor in entomology, who supervised the study as part of a dissertation by former UF doctoral student Matt Thom.
“We are increasingly faced with developing appropriate strategies to help conserve a growing list of rare organisms, including many insects,” Daniels said. “Understanding how prescribed fire and other land- management techniques impact these populations is critical to ensure their long-term survival.”
Thom also worked on the study with Leda Kobziar, a UF/IFAS associate professor in forest resources and conservation. The study appeared online May 27 in the journal PLOS ONE.
“Although we have a fairly robust understanding of how fire affects plant communities, the relationships between fire and insects is a greater mystery,” Kobziar said. “How is it that some organisms sensitive to fire also depend on specific plants that require fire to persist in a given environment? This research helps provide answers to this question, while revealing how much more we need to know to conserve the full spectrum of species through science-based fire management.”
To find out how and why some butterfly species survive fires, UF/IFAS scientists tested pupae in two North Florida forests that are typically managed with prescribed burns. Thom and his colleagues studied atala hairstreak and frosted elfin, two butterfly species that frequent fire-prone habitats.
Researchers collected data on burial depth of the frosted elfin at the Ralph E. Simmons Memorial State Forest in Nassau County. They conducted burn experiments with the atala hairstreak at the UF/IFAS Ordway Swisher Biological Station in Putnam County. They also put the pupae in laboratory baths at the UF Gainesville campus.
The atala hairstreak butterflies develop into pupae within or at the base of its host plant, while the frosted elfin sometimes goes down into the soil to pupate, Thom said.
In the experiment, scientists placed atala pupae at the soil surface and at different depths. The pupae died at the soil surface and in very shallow depths below ground, Thom said. However, when buried at 1.1 inch or more below ground, butterflies survived 75 percent to 100 percent of the time, as the temperature and the amount of heat they were exposed to decreased, Thom said. Scientists saw a similar pattern in their lab experiments.
“Butterfly pupae that bury themselves deep enough in the soil can protect themselves from fire,” said Thom.
But there are important caveats.
For example, if a non-adult atala lives in an area that’s burned, it will probably die, said Thom, now a post-doctoral scientist with the Agricultural Research Service of the U.S. Department of Agriculture. The situation also isn’t very promising for the frosted elfin. But there’s hope.
“The patchiness of fires increases where fires occur more frequently, because there’s less leaf litter. “Less material burning translates to decreased heating of the soil,” Thom said. “A more patchy fire probably means pupae on the ground have a better chance for survival, and there are more refugia for escaping adults.”
Photos credit: Matt Thom, Agricultural Research Service of the U.S. Department of Agriculture and former UF/IFAS doctoral student.