Laboratory Colonization of the Human Onchocerciasis Vector Simulium Damnosum Complex (Diptera: Simuliidae), Using an Enclosed, Gravity-Trough Rearing System

Abstract

The onchocerciasis vector Simulium damnosum s. lat. was colonized for almost 6 generations using an inexpensive, enclosed, gravity-trough rearing system designed to flood itself during power failure. Egg-to-adult survival for F₁–F₅ was 74.3, 85.5, 25.8, 17.6, and 0%, respectively. Maximum egg-to-adult survival and developmental synchrony were obtained with F₂'s reared at 25–26 °C. Insemination of females was estimated at 0.4, 6, 7, 6, and 2% for the parental–F₄ generations, respectively. Behavioral observations suggested female refractoriness prevented higher insemination rates. The male: female ratio was 1:1, 1.1:1, 0.7:1, 0.5:1, and 0.07:1 for the parental–F₄ generations, respectively. The altered sex ratios and decreased larval survival of later generations are unexplained but may indicate inbreeding depression. Sixty-six percent of emerged females (total females emerged = 4768) survived to day 2 and an average of 92.5% of these blood-fed on humans. Egg development required 72 h at 27–28 °C. An average of 65.2% of engorged females survived to day 4 and 94.6% of surviving females oviposited on cork substrates under simulated twilight conditions. Fecundity of F₂ and F₄ females was 450.50 ± 145 (n = 40, range = 200–811) and 502.79 ± 180.02 (n = 30, range = 80–836), respectively. The difference in fecundity between F₂ and F₄ females was not significant. Eleven percent of fertile eggs stored 18–20 days at 0.5–1 °C hatched.