A rapid method of estimating the abundance of immature blackflies (Diptera: Simuliidae)

A ten-point visual method of estimating the abundance of immature blackflies in the field is proposed and tested. The method is based on the comparison of larvae and pupae found on natural substrates, with ten diagrammatically prepared abundance classes. When estimates were based on the abundance of blackflies within a 4 x 4 cm area of highest density, there were no significant differences between estimates based on the ten-point visual method and those based on actual counts (P > 0.05). The time taken to assess the abundance of larval blackflies on 30 substrates was about 15 min, depending on substrate accessibility. Personal bias was assessed independently by four people, and was negligible when estimates were based on the highest densities within a 4 x 4 cm quadrat. The method tends to overlook very small larvae, and is not recommended for estimating overall population densities. However, the method provides a reliable, practical and rapid index of blackfly abundance suitable for use in blackfly control programmes.