Life history variability of a grazing stream insect (Liponeura cinerascens minor; Diptera: Blephariceridae)

SUMMARY 1. Fourteen populations of Liponeura cinerascens minor from different sites in the Swiss Alps were investigated. Our goals were to describe the life history of this blepharicerid species and to analyse how it was influenced by temperature and food availability. 2. Temperature regimes and periphyton density at the sampling sites varied considerably. Mean annual temperature ranged from 3.8 to 6.5 °C, with annual amplitudes (i.e. the difference between the mean of the coldest and the warmest month) between 3.7 and 12.0 °C. Averaged periphyton density, which was assessed semiquantitatively on a scale from 0 to 5, ranged from 1.1 to 3.3. 3. Larvae or pupae of L. c. minor were found between January and October. Presence of larvae or pupae at individual sites ranged from 100 to 224 days and appeared to be mainly a result of hatching patterns. Individual larval development required between 7 and 20 weeks. Our findings suggest that L. c. minor is univoltine and undergoes an extended (≥4 months) egg dormancy during late summer, autumn and winter. 4. Development of L. c. minor was observed from <1 to 15.8 °C, indicating it is a cold‐stenotherm. Its geographical distribution seems to be constrained by high summer temperatures. Within the tolerated temperature range (0–16 °C), however, temperature had no apparent effect on hatching, larval growth rate or pupal size. 5. Larval growth rate and size of pupae were significantly correlated with food availability. Completion of larval development required 300–400 degree‐days at sites where periphyton was readily available, but >800 degree‐days where periphyton availability was low. 6. No evidence for intraspecific food competition was found, whereas food competition by other blepharicerid species, mainly Hapalothrix lugubris, appeared to be a major reason for the observed food limitation. However, as L. c. minor is much more widespread than H. lugubris, food competition between these two species is likely to occur infrequently. We therefore contend that variations in the life history of L. c. minor are mainly a consequence of its thermal constraints.