Seasonal abundance and daily flying activity of black flies (Diptera：Simuliidae) attracted to human baits in Doi Inthanon National Park, northern Thailand

The seasonal abundance and daily flying activity of adult black flies were investigated at four different altitudes (400 m, 860 m, 1,360 m and 2,460 m) in Doi Inthanon National Park, northern Thailand. Collections were carried out at each altitude twice a month from 0600 to 1800 hours from August 2003 to July 2004, and adult black flies attracted to a human bait were captured by a hand net. The numbers of black flies collected were 2,599, 24,010, 7,996 and 4,496 at altitudes of 400 m, 860 m, 1,360 m and 2,460 m, respectively. A total of 39,101 adult black flies comprising 39,060 females, 37 males and 4 sex mosaics of 23 species of the genus Simulium Latreille s. l. were identified. Simuliid species composition and abundance varied according to altitude. Three species, i. e., S. (Gomphostilbia) asakoae Takaoka and Davies, S. (Simulium) rufibasis Brunetti and S. (S.) nigrogilvum Summers, were regularly attracted to a human bait in this order of predominance. Simulium (G.) asakoae was captured from low to medium altitudes, while S. (S.) rufibasis was captured mostly at high altitude, and S. (S.) nigrogilvum at medium altitudes. The seasonal patterns in abundance of all these predominant species varied among species even at the same altitudes and also by altitude even within the same species. Daily flying activities of these three predominant species differed in patterns and in peak hours by altitudes, by species, and also by seasons. Those of S. (G.) asakoae were similar in all seasons showing essentially a bimodal pattern with the first peak early in the morning and the second in the late afternoon, or vice versa；while S. (S.) nigrogilvum and S. (S.) rufibasis showed uni-, bi- and trimodal daily flying patterns. Five species, i. e., S. (G.) asakoae, S. (S.) chamlongi Takaoka and Suzuki, S. (S.) nigrogilvum, S. (S.) nodosum Puri and S. (S.) rufibasis, were confirmed to bite human beings.