Acta Tropica 94 (2005) 139–158 Diurnal biting periodicity of parous Simulium (Diptera: Simuliidae) vectors in the onchocerciasis Amazonian focus M.-E. Grillet a,b , N.J. Villamizar b , J. Cortez b , H.L. Frontado b,1 , M. Escalona b , S. Vivas-Mart´ ınez b,c , M.-G. Bas´ a˜ nez b,d,∗ a Laboratorio de Biolog´ ıa de Vectores, Instituto de Zoolog´ ıa Tropical, Facultad de Ciencias, Universidad Central de Venezuela, Apartado Postal 47072, Caracas 1041-A, Venezuela b Centro Amaz´ onico para Investigaci´ on y Control de Enfermedades Tropicales “Sim´ on Bol´ ıvar” (CAICET), Apartado Postal 59, Puerto Ayacucho 7101, Amazonas, Venezuela c Departamento de Medicina Preventiva y Social, Escuela Luis Razetti, Facultad de Medicina, Universidad Central de Venezuela, Caracas 1041-A, Venezuela d Department of Infectious Disease Epidemiology, Faculty of Medicine (St. Mary’s Campus), Imperial College, Norfolk Place, London W2 1PG, UK Received 3 September 2004; received in revised form 1 January 2005; accepted 2 February 2005 Abstract We describe the hourly patterns of parous biting activity of the three main simuliid vectors of human onchocerciasis in the Amazonian focus straddling between Venezuela and Brazil, namely, Simulium guianense s.l. Wise; S. incrustatum Lutz, and S. oyapockense s.l. Floch and Abonnenc. Time series of the hourly numbers of host-seeking parous flies caught in five Yanomami villages during dry, rainy, and their transition periods from 1995 to 2001 were investigated using harmonic analysis (assuming an underlying circadian rhythm) and periodic correlation (based on Spearman’s r). Parous S guianense s.l. showed a bimodal activity pattern, with a minor peak in mid-morning and a major peak at 16:00 h. S. incrustatum exhibited mainly unimodal activity during either early morning or midday according to locality. S. oyapockense s.l. bit humans throughout the day mainly between 10:00 and 16:00 h but also showed bimodal periodicity in some localities. Superimposed on the endogenous, species-specific daily cycles, parous activity showed variation according to locality, season, air temperature and relative humidity, with biting being promoted by warmer and drier hours during wet seasons/periods and reduced during hotter times in dry seasons or transitions. The results are discussed in terms of their implications for blackfly biology and ecology as well as onchocerciasis epidemiology and control. © 2005 Elsevier B.V. All rights reserved. Keywords: Simulium guianense s.l.; S. incrustatum; S. oyapockense s.l.; Time-series; Harmonic analysis; Host-seeking activity; Onchocerciasis; Southern Venezuela ∗ Corresponding author. Tel.: +44 207 5943295; fax: +44 207 4023927. E-mail address: m.basanez@imperial.ac.uk (M.-G. Bas´ a˜ nez). 1 Present address: Instituto de Altos Estudios de Salud P ´ ublica “Dr. Arnoldo Gabald´ on”, IAES-MSDS, Apartado Postal 2113, Maracay 2101-A, Aragua, Venezuela. 0001-706X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2005.02.002