Distribution pattern of black fly (Diptera: Simuliidae) assemblages along an altitudinal gradient in Peninsular Malaysia

Zubaidah Ya’cob, Hiroyuki Takaoka, Pairot Pramual, Van Lun Low, Mohd Sofian-Azirun

Preimaginal black flies (Diptera: Simuliidae) are important components of the stream ecosystem. However, there has been limited research undertaken on the vertical distribution of preimaginal black flies and their associated ecological factors. Stream conditions are generally variable along the altitudinal gradient. Therefore, we conducted an in-depth entomological survey to investigate the simuliid distribution pattern along an altitudinal gradient in Peninsular Malaysia. A total of 432 collections were performed in this study (24 samplings at each of 18 fixed-streams at monthly intervals) from February 2012 to January 2014. Larvae and pupae attached on aquatic substrates such as grasses, leaves and stems, twigs, plant roots and rocks were collected by hand using fine forceps. Stream depth (m), width (m), velocity (m/s), water temperature (°C), acidity (pH), conductivity (mS/cm) and dissolved oxygen (mg/L) were measured at the time of each collection. A total of 35 black fly species were recorded in the present study. The most frequently collected species were Simulium tani (31.7 %) and S. whartoni (21.5 %), while the relatively common species were Simulium sp. (nr. feuerborni) (16.2 %), S. decuplum (15.5 %), S. angulistylum (14.8 %), S. bishopi (13.2 %) and S. izuae (11.8 %). Total estimated species richness ranged between 39.8 and 41.3, which yielded more than 80 % of sampling efficiency. Six simuliid species were distributed below 500 m, whereas eight species were distributed above 1400 m. Simulium sp. (nr. feuerborni) and S. asakoae were found from middle to high altitudes (711-1813 m). Simulium whartoni, S. brevipar and S. bishopi were distributed widely from low to high altitudes (159-1813 m). Regression analysis between species richness and PCs revealed that the species richness was significantly associated with wider, deeper and faster streams at low altitude, normal water temperature (23-25 °C), low conductivity, higher discharge, more canopy cover and riparian vegetation and with larger streambed particles (F = 20.8, df = 1, 422, P < 0.001). Forward logistic regression indicated four species were significantly related to the stream variables (S. whartoni, Simulium sp. (nr. feuerborni), S. tani and S. angulistylum). Canonical correspondence analysis indicated that the temperature, stream size and discharge were the most important factors contributing to the separation of the stream sites from different altitude and hence are the predictors for the distribution of black fly species assemblages. This study has provided insight into the distribution pattern of preimaginal black fly assemblages along an altitudinal gradient in Peninsular Malaysia. This study could deepen our knowledge on the ecology and biology of the specialised taxa in response to environmental changes.