The biting behaviour of Blackflies Simulium damnosum, the vector of human onchocerciasis in Akamkpa Local Government Area, Cross River State, Nigeria

Abstract

The biting behaviour of Simulium damnosum was studied in Akamkpa Local Government Area of Cross River State, Nigeria between June and August, 1999.  Out of the 7604 flies collected in the entire studies, 1416, 2300 and 3888 flies were collected from Kwa-fall, Eku and Ikpan river banks respectively.  The larger number of flies in Eku and Ikpan river banks corresponded with higher mean daily rainfall, higher relative humidities and lower temperatures of these sites.  Two peaks of biting behaviour of the flies, one in the morning and another in the afternoon were observed in all the study sites.  The morning peaks for Kwa-fall, Eku and Ikpan river banks were 7.00 – 8.00 a.m.; 9.00 – 10.00 a.m. and 10.00 – 11.00 a.m. while the afternnon peaks were 12.00 – 1.00 p.m.; 2.00 – 3.00p.m. respectively.  Biting by the flies steadily decreased from 3.00 to 7.00 p.m. when they were presumed to be resting.  Out of 7,604 flies dissected, 371 (4.88%) were parous while 7,233 (95.12%) were nulliparous.  The number of parous flies reduced steadily with corresponding increase in the nulliparous flies with increasing rainfall.  The knowledge of the biting activities could be utilized in the development of appropriate control strategies for the control of onchocerciasis taking into consideration the peak biting activity of the flies which in most cases correspond with the time of outdoor working engagements of the endemic population.