Consequences for mortality by fire: The effect of pupation location of the frosted elfin, Callophrys irus Godart (Lepidoptera: Lycaenidae)

1. The imperiled frosted elfin butterfly, Callophrys irus Godart, is restricted to frequently disturbed habitats where its larval host plants, Lupinus perennis L. and Baptisia tinctoria (L.) R. Br. reside. C. irus pupae are noted to reside in the leaf litter and soil, which may allow them to escape direct mortality by fire, a major force of disturbance in many areas they inhabit. The ability (or lack of an ability) to cope with prescribed fire is a critical factor to consider in developing land management and conservation strategies in the few areas that this species remains.

2. C. irus pupa location was sampled from a well-known population at a Florida state forest with an active history of prescribed fire management. Survival of experimental surrogate butterfly pupae to the heat pulse radiated into the soil as a result of prescribed fire was tested using controlled water bath experiments and a series of prescribed fire field experiments.

3. 12 C. irus pupae were excavated from 2010 to 2012: 8 were located at the soil surface, the remaining found in the soil between 0.5-3.0cm. Survival of E. atala pupae was correlated to peak temperature and heat in the laboratory and field experiments. In addition, E. atala survival following field trials was correlated to depth of burial; complete mortality was observed for pupae at the soil surface.

4. 50% of experimental surrogate E. atala survived the heat generated by prescribed fire when at depths ≥ 1.75cm, supporting the notion that pupation in the soil at depth can protect from mortal temperatures caused by fire. If applied to depths observed for C. irus, approximately 25% of pupae would survive in the burned area. A reduction of 75% of pupae of a given C. irus population from a burn event is significant, as colony sizes in this species are typically small; decreasing the impact of prescribed fire on a population is therefore critical. Management suggestions follow those from previous studies on rare insects: divide the inhabited area into smaller units that are burned on a multi-year rotational schedule, to provide an undisturbed refuge.