The Relationship between Water Temperature and the Development Cycle Beginning and Duration in Three Black Fly Species

Understanding environmental factors affecting the timing and rate of animal development, as well as the factors that cause their effects, is of great importance. The purpose of this study was to establish the relationship between the onset and duration of the development from egg to pupal stage and water temperature in three black fly (Diptera: Simuliidae) species: Simulium (Simulium) reptans (Linnaeus 1758), Simulium (Byssodon) maculatum (Meigen 1804), Simulium (Boophthora) erythrocephalum (De Geer 1776). The study was based on surveys conducted between April and June of 1998–2010. The water temperature on the day of larval eclosion had no statistically significant impact on the beginning of development in any of the three species studied. The date when water temperature in the river reaches a certain value is important to the initiation of development in some black fly species. The present study revealed that the most important dates to the beginning of development of S. reptans black flies are when water temperature rises above 5° C, 7° C, and 10° C, while pivotal dates to the development of S. maculatum are when water temperature exceeds 4° C and 10° C. Water temperature most often exceeds the value important to the start of the development of these black fly species during March and April. The findings of the present study show that the hatching time of the two black fly species is also related to the mean water temperature in March and April. There were no statistically significant relations established between certain temperature dates and the beginning of larval development in S. erythrocephalum. Significant relations (p < 0.01) were found to exist between the duration of the development cycle from the first instar larva to pupa and the mean water temperature during the development period in S. reptans (r = -0.84; y = 53.088e⁻⁰.⁰⁸⁰⁶ˣ, R² = 0.70), S. maculatum (r = -0.82; y = 186.48e⁻⁰.¹¹²³ˣ, R² = 0.69) and S. erythrocephalum (r = -0.83; y = 58.768e⁻⁰.⁰⁶⁵²ˣ, R² = 0.70). The present study showed that the duration of development from the first instar larva to pupa in all the three black fly species studied was shorter when water temperatures during the development period were higher and longer when water temperatures were lower. The devised model of dependence between the duration of the studied black fly species' development and water temperature was verified experimentally.